Effect of splanchnicotomy on the renal excretion ofd-glucose in the anaesthetized dog

Summary The effects of acute intravenousd-glucose (G) loading were studied on anaesthetized, unilaterally splanchnicotomized (renal denervation) dogs. Glomerular filtration rate (GFR) was generally not different on the innervated and denervated side, while urine flow (V), sodium excretion (U_NaV) and urinary excretion (U_GV) of glucose on the splanchnicotomized side were significantly increased at any plasma G concentration. Tubular reabsorption (T_G) as well as Tm of G in denervated kidneys was considerably depressed. In a series of experiments with moderately elevated plasma glucose level glucosuria on the sympathectomized side was found that seems to be the consequence of a lower threshold for G in denervated kidneys. The positive correlation between the tubular reabsorption of Na and G was not influenced by renal denervation.     

Water and sodium excretion in unilaterally denervated normal and sodium depleted anesthetized rats before and after plasma volume repletion

The possible role of a reduction in plasma volume (PV) by surgery as well as the importance of dietary Na supply in denervation natriuresis have been investigated on Inactinanesthetized male rats subjected to acute unilateral renal sympathectomy. Four groups were studied: I. Normal Na diet (n=14); II. Low Na diet (boiled rice for 2 weeks)-isotonic glucose infusion (n=10); III. Low Na diet-isotonic saline infusion (n=5); IV. Normal and low Na diet rats served as conscious control (n=10). Surgery caused a 9–11% increase in hematocrit and a 15–18% decrease in PV in groups I–III. Plasma volume repletion (PVR) reverted these changes. In group I sodium excretion from both kidneys was only a fraction of that in conscious animals kept on the same diet (group IV) and marked denervation natriuresis was observed. After PVR sodium output of innervated (I) kidneys was not different from that of conscious rats but denervated (D) kidneys excreted twice that amount. In group II Na excretion was increased compared to conscious Na depleted controls, and PVR augmented further this difference. Surprisingly, the difference in urinary sodium excretion (U_NaV) between I and D kidneys was absent after surgery and was minimal after PVR in this group. In group III physiological saline infusion reverted the effect of Na depletion and denervation natriuresis was present both before and after PVR. It is concluded that PV reduction does not play a major role in denervation phenomenon. In Na depleted anesthetized rats denervation natriuresis is absent or minimal.     

Effect of splanchnicotomy on the renal excretion of uric acid in anaesthetzed dogs

Summary The renal excretion of uric acid was examined during acute i.v. urate (Ua) loading on unilaterally splanchnicotomized (renal denervation) anaesthetize mongrel dogs. Glomerular filtration rate (GFR) in general was not different in innervated and denervated kidneys, whereas urine flow (V) and urinary excretion of sodium (U_NaV) on the splanchnicotomized side were significantly increased at any plasma concentration of Ua. The excretion (U_UaV) and tubular transport (T_Ua) of urate calculated for unit GFR were considerably increased and depressed, respectively, at normal plasma Ua level and during minor urate loading (plasma concentration up to 4.7 mg%). Above this plasma level, i.e. up to 24.6 mg%, no difference in net urate reabsorption between intact and sympathectomized organs was found. It is suggested that both reabsorption and secretion of Ua in denervated kidneys are diminished.     

Change of tubular reabsorption of sodium and water after denervation

1. Renal function was compared in dogs before and after denervation, with normal or reduced glomerular filtration rate (GFR). GFR was reduced by one of two means, aortic clamping or injection of plastic microspheres into one renal artery.

2. The data showed that the tubular rejection fraction of denervated kidneys increased at a time when the same value for the control kidney decreased, indicating that denervation diuresis is not simply a result of increased filtered load of Na and water.

3. Changes in excretion after aortic clamping are not due solely to reduced filtered load. A reduction in renal blood pressure itself appears to have a direct effect on Na transport since Na excretion was significantly decreased before there were any changes in GFR, renal plasma flow and urine volume.

4. When GFR in a denervated kidney was reduced by microsphere injection it was demonstrated that a significant natriuresis (U_Na V) and diuresis (V) occurred when. GFR was reduced by as much as 40%.

5. These experiments support the hypothesis that denervation diuresis does not result solely from increased filtered load, but entails altered Na transport.

     

Atrial pressure and postprandial volume regulation in conscious dogs

Conscious, chronically instrumented dogs (n=24; left and right atrial catheter, electromagnetic flow probe around the left renal artery, carotid loop) were used in 97 expts. to study mechanisms mediating postprandial (pp) excretion of sodium and water up to at least 180 min after food intake. The dogs were kept under standardized conditions and maintained on ahigh (14.5 mmol Na/kg b.w./day) or alow (0.5 mmol Na/kg b.w./day) sodium intake diet (HSI, LSI) which was given once daily in the morning.In HSI dogs left atrial pressure (LAP) increased from a fasting control value of 0.2 kPa (2 cm H₂O) to 0.7 kPa (7 cm H₂O) (120–180 min pp), right atrial pressure from 0.0 kPa (0 cm H₂O) to 0.3 kPa (3 cm H₂O). 25% of the sodium intake were excreted up to 180 min pp. There was a highly significant positive correlation between pp sodium excretion (U _Na V) and pp LAP.U _Na V was not related to pp increase in renal blood flow (RBF) and glomerular filtration rate (GFR). Fractional sodium excretion increased from a fasting control value of 0.6% to more than 4% in HSI dogs and from 3.3% to more than 7% in anadrenalectomized HSI dog. DOCA did not diminishU _NA V in HSI dogs.In LSI dogs, RBF and GFR increased pp, LAP did not change pp. No substantial increase inU _Na V was observed.The close correlation between ppU _Na V and pp LAP in HSI dogs supports the hypothesis that intrathoracic vascular receptors are involved in the mediation of volume regulation by stimulation of still unknown natriuretic mechanisms which operate on the tubular level in the presence of high mineralocorticoid activity.     

The influence of long-term infusion of the calcium antagonist diltiazem on postischemic acute renal failure in conscious dogs

Summary The influence of long-term infusion of the calcium-entry blocker diltiazem on postischemic acute renal failure was investigated in conscious dogs monitored by implanted instruments. In 18 uninephrectomized beagle dogs on a salt-rich diet, an electromagnetic flow probe and an inflatable plastic cuff were placed around the renal artery. Acute renal failure was induced by inflating the cuff for 180 min in the conscious animal. Group A (n=5, control) received an intraaortic injection of 0.9% NaCl (5 ml/day) from the 3rd day before until the 7th day after ischemia and group B (n=6, posttreatment) an intra-aortic injection of diltizem (5 µg·min^–1·kg^–1) beginning at the end of ischemia until the 7th day. Group C (n=7, pre- and posttreatment) received diltiazem from the 3rd day before until the 7th day after ischemia. In group A, renal blood flow dropped from 149±16 (preischemic) to 129±29 ml·min^–1 on the 1st day after ischemia. In contrast, renal blood flow increased on the 1st postischemic day in both treatment groups by 29±15% (group B,P 0.05) and 14±13% (group C). In the following days, there was no significant difference in renal blood flow between groups A, B and C. In group B, the reduction of the glomerular filtration rate was similar to that in the control group. In group C, the glomerular filtration rate was significantly less reduced than in group A (34±1.8 preischemically to 17±5.4 on day 1,P 0.05 and 20±4.1 ml·min^–1 on day 7,P 0.05). Plasma renin activity increased in both diltiazem groups, more pronounced so in group B (from 3.7±1.0 on day 1 to 16.2±7.9 ng ATI·ml^–1·h^–1 on day 7,P 0.05). In contrast to groups A and B, the increase in fractional sodium excretion was less pronounced in group C. Likewise, the decrease in free water-reabsorption was less marked than in groups A or B. It was apparent that diltiazem, when administered pre- and post-ischemically, preserved glomerular filtration rate and renal blood flow. When diltizem was given solely postischemically there was an improvement in renal blood flow, but no significant influence on glomerular filtration rate. We therefore conclude that mainly tubular factors, in addition to the attenuation of postischemic vasoconstriction, are involved in the protective effect of diltiazem on postischemic acute renal failure in conscious dogs.Abbreviations ARF acute renal failure - C_osmol clearance of osmolarity - E_Na urinary excretion rate of sodium - FE_Na fractional excretion rate of sodium - GFR glomerular filtration rate - HR heart rate - NE norepinephrine - PAM mean arterial blood pressure - PRA plasma renin activity - RBF renal blood flow - RVR renal vascular resistance - T_H2_O free water reabsorption - V_U urine volume     

Renal sodium reabsorption and oxygen consumption after unilateral splanchnicotomy in the dog

Summary Experiments were carried out on pentobarbital-anaesthetized dogs previously subjected to unilateral splanchnicotomy. Renal blood flow (RBF), glomerular filtration rate (GFR), tubular reabsorption of sodium (TRF_Na), and oxygen consumption (Q _{O 2}) were determined in normal state, following isotonic volume expansion and during furosemide administration (0.5–1.5 mg/kg bw.). Denervation diuresis and natriuresis occurred under all experimental conditions. TRF_Na/Q _{O 2} was 31.4 mEq/mMol for intact and 27.7 mEq/mMol for denervated kidneys in the normal and isotonic volume expanded dogs. These values decreased significantly to 16.8 mEq/mMol and 18.3 mEq/mMol, respectively, upon furosemide loading. No difference between intact and denervated kidneys was observed in either group. TRF_Na, RBF, and GFR were significantly correlated toQ _{O 2} with no difference between intact and splanchnicotomized sides. An inhibitory effect of renal denervation on active sodium transport in the proximal tubule is suggested.     

Effects of atrial natriuretic peptide on systemic and renal hemodynamics and renal excretory function in patients with chronic renal failure

Summary We examined the effects of 60 min-hANP infusion (24 ng/min/kg) on glomerular filtration rate (GFR), renal blood flow (RBF), cardiac index (CI) and blood pressure (BP) in 8 patients with chronic renal failure (CRF) with GFR ranging from 18 to 80 ml/min/1.73 m² and in 8 control (C) subjects with normal renal function. Basal plasma levels of ANP and cGMP were elevated in CRF (ANP: 60.6±9.1 vs 13.6±1.9 pmol/l,p<0.05; cGMP: 14.3±2.9 vs 6.6±1.1 pmol/ml,p<0.05). During ANP infusion, peak levels of cGMP were higher in CRF than in C (27.5±3.2 vs. 17.3±1.3 pmol/ml,p<0.05). During ANP infusion, GFR increased in CRF by 70.7±4.2% from 34.5±6.8 to 57.4±9.9 ml/min/1.73m² (p<0.001) as compared to 16.2±1.4% in C (p<0.001 vs CRF). RBF increased in CRF by 43.6±6.4% and in C by 3.1±1.2% (p<0.01). Basal urinary sodium excretion (U_NaV) was slightly lower in CRF than in C but rose to the same level in both groups during ANP infusion. In CRF, as opposed to C, U_NaV remained elevated above baseline after the end of the infusion. The effect of ANP on fractional sodium excretion (FE_Na), however, was more pronounced in C. Basal FE_Na was higher in CRF (12.8±2.5% vs 2.4±1.5% in C,p<0.001), FE_Na remained elevated at 180% over baseline in C sixty minutes after cessation of ANP infusion, while it had returned to baseline in CRF. During ANP infusion, CI increased in CRF after 30 min from 2.91±0.08 to 3.12±0.091/min/m² (p<0.001) and in C from 3.20±0.11 to 3.39±0.13 l/min/m² (p< 0.05). Mean arterial BP was higher in CRF and its decrease was greater than in C (21.1±2.7% vs 9.1±1.0%,p<0.001). In patients with CRF GFR, RPF, and CI remained significantly elevated and BP was still significantly decreased 60 min after ANP infusion. Total peripheral vascular resistance (TPR) was elevated in CRF and declined during ANP infusion in both CRF and C. The decline of TPR was sustained and more pronounced in CRF than in C. Renal vascular resistance (RVR) was high in CRF and dropped by nearly 50% during ANP infusion, whereas only a moderate decline in RVR during ANP application was observed in C. Thus, exogenous ANP had greater and prolonged effects on systemic hemodynamics and renal function in CRF than in C. They may be due to higher levels of ANP following ANP infusion and appear to be mediated by a more sustained formation of the second messenger cGMP.Abbreviations ANP atrial natriuretic peptide - CRF chronic renal failure; - GFR glomerular filtration rate - FF filtration fraction - ERPF effective renal plasma flow - ERBF effective renal blood flow - BP blood pressure - MAP mean arterial blood pressure - HR heart rate - SV stroke volume - CO cardiac output - CI cardiac index - TPR total peripheral resistance - RVR renal vascular resistance - U_NaV urinary sodium excretion - FE_Na fractional sodium excretion - PRA plasma renin activity - ECFV extracellular fluid volume - PAH paminohippuric acid Dedicated to Prof. Dr. med. F. Krück on the occasion of his 70th birthday     

Effects of renal artery infusion of various hypertonic solutions on the renal blood flow and renal handling of PAH in the dog

Summary Effects of renal artery infusion of hypertonic solutions of glucose, mannitol, Na₂SO₄, NaCl and urea on renal blood flow (RBF) and renal handling of PAH were studied in anesthetized dogs. RBF was determined by continuous venous outflow recording and glomerular filtration rate as renal plasma flow times creatinine extraction ratio.Glucose solution increased, mannitol and Na₂SO₄ did not significantly alter while urea and NaCl depressed RBF. Only for NaCl RBF depression became greater with increasing solute loads applied. Spontaneous renal vasoconstriction and ureteral occlusion prevented RBF fall during urea and NaCl infusions. It is proposed that renal vascular reponse to local elevation of plasma osmolality is a resultant of two opposed effects: nonspecific vasodilatation as described for other vascular beds and vasoconstriction characteristic for renal vasculature and demonstrable only in normally functioning kidney.The extraction ratio of PAH (E _PAH) was not altered by hypertonic urea but decreased with the four remaining infusates. The net tubular transport of PAH fell with NaCl infusion but was not changed with glucose, Na₂SO₄, mannitol and urea. It is concluded thatE _PAH depression during NaCl infusion was due to inhibition of cellular PAH transport while that observed with glucose, Na₂SO₄ and mannitol reflected increased fraction of RBF perfusing nonsecretory renal medullary tissue.     

Ba2+ and amiloride uncover or induce a pH-sensitive and a Na+ or non-selective cation conductance in transitional cells of the inner ear

The membrane potential V _m the cytosolic pH (pH_i), the transference numbers (t) for K⁺, Cl^– and Na⁺/ non-selective cation (NSC) and the pH-sensitivity of V _m were investigated in transitional cells from the vestibular labyrinth of the gerbil. V _m, pH_i, , and the pH_i sensitivity of V _m were under control conditions were –92±1 mV (n=89 cells), pH_i 7.13±0.07 (n=11 epithelia), 0.87±0.02 (n=22), 0.02±0.01 (n=19), 0.01±0.01 (n=24) and –5 mV/pH unit (n=13 cells/n=11 epithelia), respectively. In the presence of 100 mol/l Ba²⁺ the corresponding values were: –70±1 mV (n=32), pH_i 7.16±0.08 (n=6), 0.31±0.05 (n=4), 0.06±0.01 (n=6), 0.20±0.03 (n=10) and -16 mV/pH-unit (n=15/n=6). In the presence of 500 mol/l amiloride the corresponding values were: –72±2mV (n=34), pH_i 7.00±0.07 (n=5), 0.50±0.04 (n=6), 0.04±0.01 (n=11), 0.28±0.04 (n=9) and –26 mV/pH-unit (n=20/n=5). In the presence of 20 mmol/l propionate plus amiloride the corresponding values were: –61±2 mV (n=27), pH_i 6.72±0.06 (n=5), 0.30±0.02 (n=6), 0.06±0.01 (n=5) and 0.40±0.02 (n=8), respectively. V _m was depolarized and and pH_i decreased due to (a) addition of 1 mmol/l amiloride in 150 mmol/l Na⁺ by 38±1 mV (n=8), from 0.82±0.02 to 0.17±0.02 (n=8) and by 0.13±0.01 pH unit (n=6), respectively; (b) reduction of [Na⁺] from 150 to 1.5 mmol/l by 3.3±0.5 mV (n=30), from 0.83±0.02 to 0.75±0.04 (n=9) and by 0.33±0.07 pH unit (n=4), respectively and (c) addition of 1 mmol/l amiloride in 1.5 mmol/l Na⁺ by 20±1 mV (n=11) and from 0.83±0.03 to 0.53±0.02 (n=5), respectively. These data suggest that the K⁺ conductance is directly inhibited by amiloride and Ba²⁺ and that Ba²⁺ and amiloride uncover or induce a pH-sensitive and a Na⁺/NSC conductance which may or may not be the same entity.Some of the data have been presented at various meetings and appear in abstract form in [31, 35, 37]     

The effect of phenylalanine on intracellular pH and sodium activity in proximal convoluted tubule cells of the frog kidney

The present study was performed to test the influence of sodium coupled transport of neutral substrates on intracellular pH and sodium activity in proximal tubules of the amphibian kidney. To this end, kidneys of rana esculenta have been isolated and perfused both through the portal vein (peritubular capillaries) and the aorta (luminal perfusate). The potential difference across the peritubular membrane of proximal tubule cells has been redorced with conventional (PD_pt) as well as with sodium (PD_na) and hydrogen ion (PD_h) selective microelectrodes continuously before during and after the luminal application of 10 mmol/l phenylalanine, replacing 10 mmol/l raffinose. PD_b and PD_na allowed the calculation of intracellular pH (pH_i) and sodium activity (Na_i), respectively. In the absence of phenylalanine in the tubule lumen, PD_pt approximates –57.5±2.3 mV (n=27), pH_i 7.73±0.04 (n=14, extracellular pH 7.77), and Na_i 13.3±0.9 mmol/l (n=13, extracellular sodium activity 74 mmol/l). Within 1 min the luminal application of phenylalanine leads to a depolarisation of PD_pt by +32±2 mV, as well as an increase of pH_i by 0.24±0.04 and of Na_i by 5.2±1.0 mmol/l. At 8 min from luminal application of phenylalanine, Na_i plateaus 5±1 mmol/l above control value, PD_pt increases again to a value of +12±2 mV below and pH_i decreases to a value 0.04±0.07 above their respective control values. All changes are fully reversed after removal of phenylalanine from the tubule lumen. The steady state of intracellular sodium activity might be explained by an extrusion of sodium via the sodium/potassium-ATPase, which approaches the entry across the luminal membrane, the intracellular alkalinisation is probably due to the reduced exit of bicarbonate across the peritubular cell membrane following the depolarisation of PD_pt.     

No relation between atrial natriuresis and renal blood flow in conscious dogs

Summary Conscious dogs were used to study whether changes in total renal hemodynamics are responsible for diuresis and natriuresis during an experimental increase in left atrial pressure (LAP). To ensure a controlled dietary sodium intake, the dogs (n=8) were chronically kept on ahigh or alow sodium intake diet (HSI; LSI). After the dogs had completely recovered from surgery (carotid loop, thoracotomy, flank incision), LAP was increased by about 10 cm H₂O for 60 min by tightening a purse string around the mitral annulus (51 expts). Mean urine volume (V) increased in both groups to a comparable degree. Mean sodium excretion increased somewhat more in HSI dogs, but remained elevated in LSI dogs after the LAP increase. Renal blood flow (electromagnetic flow transducer) and inulin clearance did not change. Renal vascular resistance (RVR) increased by about 20% (HSI) and 15% (LSI). — When the induced LAP increase was terminated, V decreased. RVR decreased in HSI dogs by about –11% and in LSI dogs by about –6% below control values.—It is concluded that volume regulatory mechanisms induced by an experimental LAP increase operate independently of changes in total renal blood flow.The Arbeitsgruppe Experimentelle Anästhesie is member of the Research Group Autonomic Regulations Freie Universität Berlin     

Effects of cell differentiation on ion conductances and membrane voltage in LLC-PK1 cells

LLC-PK1 cells serve as a widely used model for the renal proximal tubule. Until now, little has been found out about their membrane voltage (V _m) and ionic conductances (g). Several studies have shown changes in cell properties during differentiation and ageing. The aim of this study was to examine the relationship between V _m or g and the age of these cells. Therefore, we investigated single cells, subconfluent and confluent monolayers of LLC-PK1 cells aged 1–8 days with the slow-whole-cell patch-clamp technique. The V _m of all cells was-34±2 mV (n=75) and the membrane conductance (g _m) was 2.3±0.3 nS (n=30). V _m in cells aged up to 2 days was-24±3 mV (n=22) whereas V _m in cells aged 5–8 days was -50±3 mV (n=15). An increase of extracellular K⁺ from 3.6 to 18.6 mmol/l led to a depolarization in all cells of 4±1 mV (n=31) and an increase of g _m by 17±13% (n=15). Complete replacement of extracellular Na⁺ by N-methyl-D-glucamine (NMDG) led to a hyperpolarization of 19±2 mV (n=38) and g_m was lowered by 27±14% (n=17). A reduction in extracellular Cl^– from 147 to 32 mmol/l showed no significant effect on V _m (n=16) or g _m (n=11). Amiloride (10 mol/l) had no significant effect on V _m (n=13) or g _m (n=7). The reduction of the extracellular osmolarity from 290 to 160 mosmol/l led to a hyperpolarization of 11±1 mV (n=18) and an increase in g _m by 326±117% (n=12). There was no significant correlation between g _m and cell age. LLC-PK1 cells used in this study have a K⁺ conductance and a non-selective cation conductance in parallel. With increasing age, LLC-PK1 cells became more and more conductive for K⁺ and lost their nonselective cation conductance. There is no evidence for a significant amiloride-sensitive Na⁺ or Cl^– conductance in these cells. The K⁺ conductance could be activated by osmotically induced cell swelling.     

The cardioplegic solution HTK: effects on membrane potential,intracellular K+ and Na+ activities in sheep cardiac Purkinje fibres

The effects of the cardioplegic solution HTK on membrane potential (E_M) and intracellular K and Na activities (a _K ⁱ , a _Na ⁱ ) were studied in sheep cardiac Purkinje fibres by means of conventional and ion-selective microelectrodes. HTK contains (mM): Na 15, K 10, Ca 0, Mg 4, histidine 180, (1) In control conditions E_M was –74.3±3.3 mV (n=25), a _K ⁱ was 116.4±4.1 mM (n=7) and a _Na ⁱ was 8.2±1.4 mM (n=15). (2) Exposure to HTK led to a depolarization to –59.7±3.6 mV (n=25) which exceeded by about 5–7 mV that induced in a Tyrode solution of 10 mM K and in a modified HTK solution supplemented by 2 mM Ca (n=6). (3) Addition of 0.5 mM barium eliminated the difference in the steady-state depolarization. (4) HTK superfusion increased a _K ⁱ to 120.1±4.4 mM (n=7) and decreased a _Na ⁱ to 3.9±0.9 mM (n=15). (5) The decrease in a _Na ⁱ was insensitive to amiloride (1 mM) and to external alkalization but was slightly increased by addition of 2 mM calcium. (6) When the calcium in Tyrode solution was lowered from 2.0 mM to 0.05 mM, a _Na ⁱ hardly decreased during subsequent exposure to unmodified HTK and it increased in the presence of 0.1 mM dihydroouabain. We propose the hypothesis (1) that the difference in membrane depolarization between HTK and a 10 mM K-Tyrode is caused by a decrease in K conductance by the HTK solution and (2) that the a _Na ⁱ decline mainly results from a coupled Ca influx via Na-Ca exchange due to a delayed washout of external calcium.This work was supported by the Deutsche Forschungsgemeinschaft, SFB 330 — Organprotektion     

Endothelin-1 blunts transepithelial transport and differentiation of Madin-Darby canine kidney cells

We investigated the effects of endothelin-1 (ET-1) on Madin-Darby canine kidney (MDCK) cells, a cell line originating from the renal collecting duct. The activity of transepithelial transport was assessed as the rate of dome formation in monolayers grown on solid support. The pH value of the dome fluid (dome pH) was measured by means of pH-selective microelectrodes. Differentiation of monolayer cells was estimated as the peanut-lectin(PNA)-binding capacity of the apical membrane. Confluent monolayers were incubated for 12–72 h in serum-free medium at various concentrations of ET-1. Exposure to 1 nmol/l ET-1 reduced dome formation by a maximum of 41±8% (n=4; P<0.02) after 24 h. ET-1 (10 nmol/l; 24 h) decreased dome pH from 7.52±0.02 (n=53) to 7.36±0.03 (n=51; P<0.02). Apical application of amiloride (1 mmol/l) reduced dome pH in both ET-1-treated and non-treated domes to essentially the same level, 7.25±0.03 (n=19) and 7.23±0.03 (n=17) respectively. ET-1 (10 nmol/l; 24 h) reduced PNA-binding capacity by 19±3% (n=5; P < 0.02). Moreover, ET-1 prevented the increase in PNA binding (+53±7%; n=5) induced by 0.1 mol/l aldosterone. We conclude that ET-1 inhibits transepithelial transport and PNA binding via inhibition of apical Na⁺/H⁺ exchange, thus antagonizing aldosterone action in MDCK cells.     

Electrophysiological characterization of rabbit distal convoluted tubule cell

The distal convoluted tubule (DCT) from rabbit kidney were perfused in vitro to study the conductive properties of the cell membranes by using electrophysiological methods. When the lumen and the bath were perfused with a biearbonate free solution buffered with HEPES, the transepithelial voltage (V _T) averaged –2.8±0.6 mV (n=20), lumen negative. The basolateral membrane voltage (V _B) averaged –77.8±1.1 mV (n=33) obtained by intracellular impalement of microelectrodes. Cable analysis performed by injecting a current from perfusion pipette revealed that the transepithelial resistance was 21.8±1.7 ·cm² and the fractional resistance of the luminal membrane was 0.78±0.03 (n=8), indicating the existence of ionic conductances in the luminal membrane. Addition of amiloride (10^–5 mol/l) to the luminal perfusate or Na⁺ removal from the lumen abolished the lumen negativeV _T and hyperpolarized the apical membrane. An increase in luminal K⁺ concentration from 5 to 50 mmol/l reduced the apical membrane potential (V _A) by 37.5±2.6 mV (n=7), whereas a reduction of Cl^– in the luminal perfusate did not changeV _A significantly (0.5±0.5 mV,n=4). Addition of Ba²⁺ to the lumen reducedV _A by 42.6±1.0 mV (n=4). When the bathing fluid was perfused with 50 mmol/l K⁺ solution, the basolateral membrane voltage (V _B) fell from –76.8±1.5 to –31.0±1.3 mV (n=18), and addition of Ba²⁺ to the bath reducedV _B by 18.3±4.8 mV (n=7). Although a reduction of Cl^– in the bathing fluid from 143 to 5 mmol/l did not cause any significant fast initial depolarization (1.8±1.7 mV,n=8), a spike like depolarization (14.0±2.5 mV,n=4) was observed, upon Cl^– reduction in the presence of Ba²⁺ in the bath. From these results, we conclude that the apical membrane of DCT has both K⁺ and Na⁺ conductances and the basolateral membrane has a K⁺ conductance and a small Cl^– conductance.     

Effects of increased cardiac mechanical performances on flow rates of cardiac lymph in dogs

Summary Relationship between flow rates of cardiac lymph (LF), and coronary blood flow (CF), coronary perfusion pressure (PP), left ventricular peak systolic pressure (LVSP) and heart rate (HR) was studied in open-chest dogs. Intra-coronary administration of catecholamines (CA) and electrical stimulation of the cardiac sympathetic nerve (ES) increased LF transiently with a concomitant rise in the cardiac mechanical performance, while dipyridamole induced no change in LF in spite of a marked increase in CF. Isoproterenol at doses of 0.3 and 3×10^–8 g/kg induced an increase in LF to 119±4 and 167±20% (mean ±SE); norepinephrine, 0.3 and 3×10^–7 g/kg, to 118±4 and 141±13%; ES at 5 and 20 Hz, to 135±11 and 167±10%, respectively. Peak responses of LF correlated with changes in LVSP (r=0.59,n=51,P<0.001), CF (r=0.53,n=51,P<0.001), PP(r=0.49,n=51,P<0.001) but not with changes in HR (r=0.27,n=51, 0.05<P<0.10). Cardiac pacing also showed a poor correlation between the changes in LF and HR under the same LVSP within the changes in HR up to 134% of control value (r=–0.12,n=17,P>0.50). It is concluded that LF is independent of changes in HR, and increased LF after CA or ES may be caused mainly by an augmented propulsive force.     

Acid base status in unanesthetized,unrestrained guinea pigs

Acid-base status of arterial blood was measured in chronically cannulated, unanesthetized, unrestrained guinea pigs. Normal values were: pH=7.444±0.032,PaCO₂=35.7±4.4; HCO ₃ ^– =24.4±2.8; BE=+0.4±2.1 (n=69) andPaO₂=91.9±7.3 (n=25) (Values are mean±S.D.).Induction of light anesthesia with thiopentone caused a respiratory depression (decrease inPaO₂) accompanied by respiratory acidosis (increase inPaCO₂ and decrease in pH) and a development of slight metabolic acidosis (decrease in base excess and standard bicarbonate). Acid base parameters of guinea pigs are compared to those obtained from rats under identical experimental conditions.     

Noise analysis of cAMP-stimulated Na current in frog colon

The effects of oxytocin and cAMP on the electrogenic Na⁺-transport in the short-circuited epithelium of the frog colon (Rana esculenta, Rana temporaria) were investigated. Oxytocin (100 mU · ml^–1) elevated the shortcircuit current (I _sc) transiently by 70% whereas cAMP (1 mmol · l^–1) elicited a comparable sustained response. The mechanism of the natriferic action of cAMP was studied by analysing current fluctuations through apical Na⁺-channels induced by amiloride or CDPC (6-chloro-3,5-diaminopyrazine-2-carboxamid). The noise data were used to calculate Na⁺-channel density (M) and single apical Na⁺-current (i _Na).i _Na-Values obtained with amiloride and CDPC were 1.0±0.1 pA (n=5) and 1.1±0.2 pA (n=6) respectively and unaffected by cAMP. On the other hand, cAMP caused a significant increase in M from 0.23±0.08 m^–2 (n=5) to 0.49±0.17 m^–2 (n=5) in the amiloride experiments. In our studies with CDPC we obtained smaller values for M in control (0.12±0.04 m^–2;n=6) as well as during cAMP treatment (0.19±0.06 m^–2;n=6). However, the cAMP-induced increase in M was also significant. We conclude that cAMP stimulates Na⁺-transport across the frog colon by activating silent apical Na⁺-channels. Thus, the mechanism of regulation of colonic Na-transport in frogs differs considerably from that in other vertebrates as mammals and birds.     

Examination of possible renal origin of the humoral factor responsible for saline diuresis in the dog

Summary The hypothesis of renal origin of the humoral factor responsible for the natriuresis which follows saline infusion in the dog was tested in a cross-circulation model especially designed for the purpose. Renal venous blood of saline loaded donor dogs was pumped directly into the system perfusing the right (assay) kidney of oliguric recipient animals. In control and recovery periods, recipients own renal venous blood was substituted for the blood of saline-infused donors.Sodium excretion increased slightly from the control value of 2.8±1.2 (S.D.) to 4.7±3.5 Eq/min (68 per cent increase,p<0.05), but only slight recovery toward control rate was noted within 25 min of cessation of cross-circulation. Simultaneously, filtered sodium decreased slightly from 2.8±1.15 (S.D.) to 2.7±1.10 mEq/min. Glomerular filtration rate (C _CR) and effective renal plasma flow (C _PAH) decreased gradually during the experiment. Urine flow,U/P _osm, hematocrit, and perfusion pressure of the assay kidney showed only minor changes.Since the slight increase in sodium excretion during cross-circulation constituted but a small fraction of natriuresis observed in saline-loaded donors, it was concluded that the results are incompatible with the release from the kidney of saline-infused animals of a potent natriuretic factor.This study was supported by American Heart Association Grant 66630.