Effects of epinephrine on electrical properties of Madin-Darby canine kidney cells

The present study has been performed, to test for the influence of epinephrine on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK) cells. Under control conditions, mimicking the in vivo situation, PD averages –53.3±0.9 mV (n=37). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +4.3±0.4 mV (n=5) and +15.8±1.2 mV (n=5), respectively. The application of 1 mol/l epinephrine leads to sustained hyperpolarization of the cell membrane to –71.5±0.7 mV (n=37). In the presence of epinephrine, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +30.6 ±0.2 mV (n=5); 1 mmol/l barium depolarizes the cell membrane by +14.8±0.7 mV (n=20) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, epinephrine leads to a transient hyperpolarization by –31.2 ±1.2 mV (n=18). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium; 10 mol/l verapamil depolarizes the cell membrane to –41.0±2.6 mV (n=11). In the presence of verapamil, the hyperpolarizing effect of epinephrine is only transient; 10 mol/l phentolamine depolarizes the cell membrane by +3.0±0.6 mV (n=8). In the presence of phentolamine, the effect of epinephrine is virtually abolished (+0.4±0.6 mV,n=8); 1 mol/l isoproterenol depolarizes the cell membrane by +2.8±0.8 mV (n=8). In the norminal absence of extracellular calcium, epinephrine leads to a transient hyperpolarization, which can only be elicited once. In conclusion, cpinephrine hyperpolarizes MDCK cells by increasing the apparent potassium conductance. This effect is transmitted by -receptors and may be mediated by increases of intracellular calcium activity.     

Effects of bradykinin on electrical properties of Madin-Darby canine kidney epithelioid cells

In the present study we have investigated the influence of bradykinin on the potential difference across the cell membrane (PD) of Madin Darby Canine Kidney (MDCK)-cells. In the absence of bradykinin PD averages –52.6±0.9 mV (n=52). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +5.2±0.3 mV (n=8) and +14.9±1.0 mV (n=9), respectively. The application of 0.1 mol/l bradykinin leads to a transient hyperpolarization of the cell membrane to –70.3±0.6 mV (n=30). During this transient hyperpolarization increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +10.4±0.7 mV (n=10) and +29.2±0.8 mV (n=8) respectively. Application of fragments of bradykinin (0.1 mol/l) are without significant effect on the potential difference across the cell membrane. 1 mmol/l barium depolarizes the cell membrane by +15.8±1.2 mV (n=9) and abolishes the effect of step increase of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, bradykinin leads to a transient hyperpolarization by –24.7±1.3 mV (n=7). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. In the nominal absence of extracellular calcium, bradykinin leads to a transient hyperpolarization, which can be elicited only once. The transient hyperpolarization is not affected by the presence of verapamil or indomethacin. In conclusion, bradykinin hyperpolarizes MDCK-cells by increasing the apparent potassium conductance. This effect is probably mediated by increase of intracellular calcium activity.     

Electrical properties of Madin-Darby canine kidney cells

To gain some insight into electrogenic transport processes across the plasma membrane of Madin-Darby canine kidney (MDCK)-cells, continuous measurements of the potential difference across the plasma membrane (PD) were made during step changes of extracellular ion composition as well as application of barium or valinomycin. During control conditions mimicking in vivo extracellular fluid, PD approaches –51.5±0.8 mV (n=62). Step increase of extracellular potassium concentration from 5.4 to 10, to 20 or to 35 mmol/l, depolarizes PD by +5.5±0.8 mV (n=7), by +15.8±0.5 mV (n=64) and by +23.8±1.2 mV (n=12), respectively. 1 mmol/l barium depolarizes PD by +19.8±0.6 mV (n=38) and abolishes the effect of increasing extracellular potassium from 5.4 to 10 mmol/l but not to 35 mmol/l. Ten mol/l valinomycin hyperpolarizes PD to –69.3±2.9 mV (n=7). In the presence of valinomycin, increase of extracellular potassium from 5.4 to 20 mmol/l depolarizes PD by +31.0±1.0 mV (n=7). Ouabain depolarizes PD and reduces the sensitivity of PD to extracellular potassium concentration. Omission of extracellular bicarbonate and carbondioxide as well as increase of extracellular bicarbonate at constant carbondioxide lead to a hyperpolarization and enhanced sensitivity of PD to extracellular potassium. In the presence of barium, the effects of omitted bicarbonate and carbondioxide are only transient. In conclusion, the plasma membrane of MDCK-cells is highly conductive to potassium. At low but not at high extracellular potassium concentrations the potassium conductance can be blocked by barium. The potassium conductance can further be reduced by ouabain as well as acidosis and enhanced by alkalosis as well as omission of extracellular carbondioxide and bicarbonate.     

Effects of serotonin on electrical properties of Madin-Darby canine kidney cells

The present study has been performed to test for the influence of serotonin on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK)-cells. Under control conditions PD averages –48.6±0.6 mV (n=98). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +6.3±0.6 mV (n=6) and +14.1±1.0 mV (n=12), respectively. The cell membrane is transiently hyperpolarized to –67.8±0.8 mV (n=63) by 1 mol/l serotonin. In the presence of serotonin, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +26.4±1.0 mV (n=11). 1 mmol/l barium depolarizes the cell membrane by +15.7±1.3 mV (n=17) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, serotonin leads to a transient hyperpolarization by –26.3±1.0 mV (n=16). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. 10 mol/l methysergide hyperpolarize the cell membrane by –7.2±2.0 mV (n=6). In the presence of 10mol/l methysergide, the effect of serotonin is virtually abolished (+0.4±0.9 mV,n=6). 1 mol/l ketanserin, a 5-HT₂ receptor blocking agent, ICS 205-930, a 5-HT₃ receptor blocking agent, and phentolamine, an unspecific -receptor blocking agent, do not significantly modify the effect of serotonin. In the nominal absence of extracellular calcium, the effect of serotonin is markedly reduced. In conclusion, serotonin hyperpolarizes MDCK-cells by increasing apparent potassium conductance. This effect is transmitted by 5-HT₁ receptors and depends on extracellular calcium.     

Electrical properties of Madin-Darby-canine-kidney cells

In incompletely confluent madin Darby canine kidney cells continuous measurements of the potential difference across the cell membrane (PD) were made with conventional microelectrodes during rapid changes of extracellular sodium and/or calcium concentration. During control conditions PD averages –50.6±0.7 mV. Reduction of extracellular sodium concentration from 131.8 to 17.8 mmol/l leads to a reversible hyperpolarization of the cell membrane to –65.3±1.1 mV. This hyperpolarization is not significantly reduced by omission of glucose or presence of amiloride (1 mmol/l) in the perfusates. Instead, 1 mmol/l amiloride depolarizes the cell membrane by +5.2±0.4 mV. 1 mmol/l barium depolarizes the cell membrane to –31.3±1.1 mV. Step increases of extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarize the cell membrane by +5.5±0.5 mV and +16.5±1.8 mV respectively. In the presence of barium, the depolarizing effect of increasing extracellular potassium concentration and of amiloride is almost abolished. Reduction of extracellular sodium concentration in the presence of barium, however, leads to a transient hyperpolarization of the cell membrane. During this transient hyperpolarization, increasing extracellular potassium concentration depolarizes the cell membrane despite the continued presence of barium. Omission of extracellular calcium (EDTA) depolarizes the cell membrane by +36.7±3.2 mV. In the absence of extracellular calcium, the hyperpolarizing effect of reduced extracellular sodium concentration is markedly reduced (–4.5±1.2 mV). 2 mol/l A23187 in the presence of extracellular calcium hyperpolarizes the cell membrane to –72.5±0.6 mV. In conclusion, reduction of extracellular sodium concentration increases the potassium conductance of the cell membrane, possibly by increasing intracellular calcium activity via an influence on the sodium/calcium-exchange.     

The effect of phenylalanine on the electrical properties of proximal tubule cells in the frog kidney

The present study was designed to elucidate the effects of sodium-coupled transport on the electrical properties of proximal tubule cells in the isolated perfused frog kidney. Cable analysis techniques have been employed to determine the resistance of the luminal and peritubular cell membranes in parallel (R _m) and the apparent ratio of the luminal over the peritubular cell membrane resistance (VDR). Furthermore, the sensitivity of the potential difference across the peritubular cell membrane (PD_pt) to 6-fold increases of peritubular potassium concentration (PD_k) was taken as a measure of the relative potassium conductance of this membrane. In the absence of luminal phenylalanine, PD_pt amounts to –60±1 mV (n=90),R _m to 36±3 k cm (n=22), VDR to 1.81±0.14 (n=20), and PD_k to 15.0±0.9 mV (n=25). The application of 10 mmol/l phenylalanine replacing 10 mmol/l raffinose leads to a rapid (within 30 s) depolarisation of PD_pt to 50±5% of its control value and to a delayed (within 12 min) recovery to 95±5% of control. The rapid depolarisation is associated with a decline ofR _m and VDR, indicating a decrease mainly of the luminal cell membrane resistance. During recovery of PD_pt there is a parallel increase of VDR and a further decline ofR _m pointing to a decline of the basolateral cell membrane resistance. PD_k is decreased during rapid depolarisation but increases again during the recovery phase. Thus, phenylalanine initially decreases but then increases above control the apparent potassium conductance. Removal of phenylalanine leads to a transient hyperpolarisation and increased apparent potassium conductance. If a cell is depolarised by current injection into a neighbouring cell, a similar decrease of PD_k is observed which shows also a similar recovery (partial repolarisation) despite continued injection of constant current. The data point to a potential-dependent peritubular K⁺-conductance (of the inwardly rectifying type) and to a regulatory increase within some ten minutes, when the cell is depolarised either by sodium entry across the luminal cell membrane or by current injection into a neighbouring cell.     

Electrical properties of Ehrlich ascites tumor cells

The cell membrane potential (PD) of Ehrlich ascites tumor cells was measured continuously at 37°C with conventional microelectrodes during rapid alterations of extracellular fluid composition. At extracellular electrolyte composition mimicking the in vivo situation PD is –56.7±0.7 mV and the apparent membrane resistance is 62.2±2.2 M. Increasing extracellular potassium concentration from 5.4 to 20.0 mmol/l depolarizes the cell membrane by +18.4±0.5 mV. Thus, the transference number for potassium (tk, apparent slope potassium conductance over slope membrane conductance) is 0.53±0.01. A significant correlation is observed between tk and PD: tk=–(0.014±0.001) [1/mV]·PD [mV] –(0.243±0.051). 0.7 mmol/l barium depolarizes the cell membrane by +28.2±0.7 mV, increases the apparent membrane resistance by a factor of 2.6±0.1 and abolishes the apparent potassium conductance. Reduction of extracellular sodium concentration from 141 to 21 mmol/l depolarizes the cell membrane by +3.1±1.3 mV. Similarly, 0.1 mmol/l amiloride depolarizes the cell membrane by +3.3±0.7 mV. Reduction of extracellular chloride concentration from 128 to 67 mmol/l hyperpolarizes the cell membrane by –2.5±0.2 mV. 1 mmol/l anthracene-9-COOH does not significantly alter PD. Temporary omission of glucose from the extracellular fluid has no appreciable effect on PD. In conclusion, PD of Ehrlich ascites tumor cells is in the range of other mammalian epithelial cells and is generated mainly by potassium diffusion, while the conductances to sodium and chloride appear to be small.     

Regulation of potassium conductance by prostaglandins in cultured renal epitheloid (Madin-Darby canine kidney) cells

Madin-Darby canine kidney (MDCK) cells form arachidonic acid metabolites following stimulation of several hormones known to modify the ion conductances at the plasma membrane. The present study has been performed to elucidate the influence of arachidonic acid on the electrical properties of subconfluent MDCK cells. As a result, arachidonic acid (1 or 10 mol/l) leads to a transient hyperpolarization of the cell membrane, followed by a transient depolarization and a second, sustained hyperpolarization. The effects are inhibited by cycloxygenase inhibitor indomethacin (1 mol/l). The initial transient hyperpolarization is mimicked by prostaglandin E₂ (PGE₂, 0.1 mol/l), the sustained hyperpolarization by both PGE₂ (0.1 mol/l) and PGF₂ (0.1 mol/l). The transient hyperpolarization is paralleled by an increase of potassium selectivity and a decrease of cell membrane resistance and is thus the result of increased potassium conductance. The transient depolarization is paralleled by an increase of chloride selectivity, reflecting an increase of chloride conductance. The sustained hyperpolarization is paralleled by an increase of cell membrane resistance, and increase of potassium selectivity and a decrease of chloride selectivity, and is thus the result of decreasing chloride conductance. The observations reveal a role of prostaglandins in the regulation of ion conductances in MDCK cells, which could well participate in the transport regulation by hormones.     

Further characterization of volume regulatory decrease in cultured renal epitheloid (MDCK) cells

In Madin Darby canine kidney (MDCK) cells volume regulatory decrease (VRD) is paralleled by a variable, transient hyperpolarization followed by a sustained depolarization of the cell membrane. In the depolarized cells, the cell membrane selectivity is decreased for potassium and increased for chloride. Without knowledge of the cell membrane resistance (R _m), these changes of cell membrane selectivity cannot be translated into conductances, i.e. the observed alterations of ion selectivity could have been due to inhibition of potassium conductance or activation of anion conductance. In the present study R _m has been determined by cellular cable analysis. To this end, three microelectrodes were impaled into three different cells of a cell cluster, current (up to 3 nA) was injected into one cell and the corresponding voltage deflections determined in the other two cells. As a result, exposure of the cells to hypotonic perfusates leads to a marked, sustained reduction of R _m. In the absence of chloride and in the absence of bicarbonate and chloride, the decrease of R _m is only transient. The data indicate that cell swelling leads to a transient increase of potassium conductance followed by a sustained increase of anion conductance. As evident from BCECF fluorescence, exposure of MDCK cells to hypotonic perfusates leads to a significant decrease of intracellular pH, which may in part be due to loss of bicarbonate through the anion conductive pathway.     

Electrophysiology of cell volume regulation in proximal tubules of the mouse kidney

The present study has been designed to test for the influence of cell swelling on the potential difference and conductive properties of the basolateral cell membrane in isolated perfused proximal tubules. During control conditions the potential difference across the basolateral cell membrane (PD_bl) is –65±1 mV (n=74). Decrease of peritubular osmolarity by 80 mosmol/l depolarizes the basolateral cell membrane by +7.8±0.5 mV (n=42). An increase of bath potassium concentration from 5 to 20 mmol/l depolarizes the basolateral cell membrane by +25±1 mV (n=11), an increase of bath bicarbonate concentration from 20 to 60 mmol/l hyperpolarizes the basolateral cell membrane by –3.2±0.5 mV (n=13). A decrease of bath chloride concentration from 79.6 to 27 mmol/l hyperpolarizes the basolateral cell membrane by –1.8±0.7 mV (n=6). During reduced bath osmolarity, the influence of altered bath potassium concentration on PD_bl is decreased ( PD_bl=+16±2 mV,n=11), the influence of altered bicarbonate concentration on PDbl is increased ( PD_bl=–6.0±0.8 mV,n=13), and the influence of altered bath chloride concentration on PD_bl is unaffected ( PD_bl=–1.8±0.6 mV,n=6). Barium depolarizes the basolateral cell membrane to –28±2 mV (n=16). In the presence of 1 mmol/l barium, decrease of peritubular osmolarity by 80 mosmol/l leads to a transient hyperpolarization of the basolateral cell membrane by –5.9±0.5 mV (n=16). This transient hyperpolarization is blunted in the absence of extracellular bicarbonate. In conclusion, cell swelling depolarizes straight proximal tubule cells and increases bicarbonate selectivity of the basolateral cell membrane at the expense of potassium selectivity. The data reflect either incrases of bicarbonate conductance or decrease of potassium conductance during exposure of proximal tubule cells to hypotonic media.Parts of this work were presented at the 18th Congress of the Gesellschaft für Nephrologie, Frankfurt/M. 1986 and at the 8th International Symposium on Biochemical Aspects of Kidney Function, Dubrovnik 1986     

Influence of potassium depletion on potassium conductance in proximal tubules of frog kidney

In order to test for the contribution of intracellular potassium activity to the link of sodium/potassium-ATPase activity and potassium conductance, studies with conventional and potassium selective microelectrodes were performed on proximal tubules of the isolated perfused frog kidney. The peritubular transference number for potassium (t _k), i.e., the contribution of peritubular slope potassium conductance to the slope conductance of the cell membranes (luminal and peritubular), was estimated from the influence of peritubular potassium concentration on the potential difference across the peritubular cell membrane (PD _pt). During control conditions,PD _pt is –65±1 mV, intracellular potassium activity (K _i) 57±2 mmol/l andt _k 0.41±0.05. The resistance in parallel of the luminal and peritubular cell membranes (R _m) is 44±4 kcm, the resistance of the cellular cable (R _c) 137±13 M/cm. When the cells are exposed 10 min to potassium free perfusates (series I),PD _pt increases by –28±3 mV within 2 min and then decreases gradually to approach the control value within 10 min.K _i decreases by 22±3 mmol/l andR _c increases by 35±10%. After a transient decrease,R _m increases by 36±9%. Readdition of peritubular potassium leads to a transient increase ofPD _pt, a gradual decrease ofR _m andR _c as well as a gradual increase ofK _i t _k recovers only slowly to approach 65±8% of control value within 3 and 79±10% within 6 min. When the cells are exposed 10 min to potassium free perfusates containing 1 mmol/l barium (series II),PD _pt depolarizes by +28±4 mV andK _i decreases by 7±1 mmol/l within 10 min. Within 2 min of reexposure to control perfusatesPD _pt approaches the control value.t _k recovers significantly faster than in series I and approaches 92±8% of control value within 3 min and 107±8% within 6 min reexposure to control perfusates. In conclusion, the effect of potassium free perfusates on peritubular potassium conductance depends on the degree of potassium depletion of the cell.     

Membrane electrical properties of vascular smooth muscle from the guinea pig superior mesenteric artery

Some electrical membrane properties of an isolated small artery, namely, the superior mesenteric artery of the guinea pig, were studied by intracellular microelectrodes. The mean resting membrane potential (E _m) was –54 mV. The average slope of theE _m vs. log [K]_o curve (between 10 and 100 mM [K]_o) was 32 mV/decade, and the curve extrapolated to a [K]_i of 160 mM. The ratio of Na⁺ permeability to K⁺ permeability (P _Na/P _K) at 4.0 mM [K]_o calculated from the Goldman constant-field equation (assuming Cl^– to be passively distributed) was 0.18 (E _m=–46 mV after a 5 min exposure to ouabain to suppress any electrogenic pump potential). The normal input resistance (R _in) averaged 8.5 m. Choline substitution for Na⁺ or amiloride, an agent known to depressP _Na, hyperpolarized the muscle to about –63 mV without a significant change inR _in. Ba²⁺ (0.5 mM) depolarized the muscle to –37 mV, increasedR _in to 15 m, and produced spontaneous action potentials in this normally quiescent artery; tetraethylammonium (TEA, 5 mM) enabled large overshooting action potentials to be produced upon stimulation. Glutamate of NO ₃ ^– substitution for Cl^– produced an initial depolarization followed by a return to the original resting potential within 10 min; readdition of 25 mM Cl^– transiently hyperpolarized the muscle markedly, followed by a return to the originalE _m. These data indicate that Cl^– is passively distributed and does not contribute to the steady-state resting potential in this vascular muscle. The data also suggest that the relatively lowE _m in this arterial muscle is not due to a low [K]_i, but is due to a highP _Na/P _K ratio, presumably related to a low K⁺ conductance (g _K). Since Ba²⁺ and TEA⁺ are known to decrease restingg _K and K⁺ activation, the data also suggest that K⁺ activation could inhibit action potential generation.     

Influence of barium on the effects of phenylalanine in proximal tubules

The present study was designed to further test for the role of peritubular potassium conductance in the repolarization of peritubular cell membrane during sustained stimulation of sodium coupled transport by phenylalanine. To this end the potential difference across the peritubular cell membrane (PDpt) has been recorded continuously, while 10 mmol/l phenylalanine (Phe) were added to the luminal perfusate, both in the presence or absence of peritubular or luminal barium (1 mmol/l). In the absence of phenylalanine and barium, PDpt amounts to –65.5±2.2 mV. Phe leads to a rapid depolarization of the peritubular cell membrane by +36.2±2.2 mV within 30 s, followed by an almost complete repolarization by –28.9±2.6 mV within 7 min. In the presence of barium in peritubular perfusate, the depolarization following Phe is +24.3±2.6 mV and the repolarization almost abolished (–4.3±0.9 mV). In the presence of barium in luminal perfusate, Phe leads to a depolarization by +35.7±2.4 mV followed by a repolarization of –17.0±3.2 mV within 7 min. It is concluded that the repolarization during sustained stimulation of sodium coupled transport is in large part due to alterations of peritubular potassium conductance.     

Influence of mepacrine,indomethacin, and nordihydroguaiaretic acid on the electrical properties of frog renal proximal tubules

In proximal renal tubules of the frog kidney, stimulation of sodium-coupled transport leads to a depolarization of the peritubular cell membrane, followed by partial repolarization. These alterations of the potential difference across the peritubular cell membrane (PD_pt,) are in part the result of altered peritubular potassium conductance. The repolarization has been blunted by the phospholipase A₂ inhibitor mepacrine, but not by the cyclooxygenase inhibitor indomethacin. In the present study the effect of mepacrine, indomethacin and the lipoxygenase inhibitor nordihydroguaiaretic acid on the electrical properties of proximal renal tubules has been tested in the presence and absence of stimulated sodium-coupled transport. In the absence of inhibitors, addition of 10 mmol/l phenylalanine to the luminal perfusate leads to a rapid depolarization and partial repolarization of the peritubular cell membrane, a decrease of the luminal cell membrane resistance (R _a) and a small increase of the cellular core resistance (R _c). Removal of phenylalanine leads to rapid hyperpolarization, increase of R _a and decline R _c. Mepacrine (100 ol/l) depolarizes the cell membrane and increases the peritubular cell membrane resistance (R _b), R _c and the intracellular pH. In the presence of mepacrine, phenylalanine leads to a sustained depolarization and a transient decrease of R _a. Indomethacin (10 mol/l) does not significantly modify PD_pt, the lumped resistance of both cell membranes (R _m) or R _c in the presence or absence of phenylalanine. Nordihydroguaiaretic acid (50 mol/l) does not alter significantly PD_pt, R _a, R _b or R _c prior to phenylalanine. However, in the presence of nordihydroguaiaretic acid, the repolarization upon phenylalanine is significantly more rapid, and the removal of phenylalanine in the presence of nordihydroguaiaretic acid is followed by a significant decrease of both, R _a and R _b. The observations point to an involvement of eicosanoids in the regulation of ion conductances during stimulation of sodium-coupled transport.     

Effects of ischaemia and post-ischaemic reperfusion on the passive and active electrical parameters of rat skeletal muscle fibres

Electrical parameters of extensor digitorum longus (EDL) muscles and their contralaterals were measured in vitro at 30°C by a computerized two intracellular microelectrode technique after ischaemia and postischaemic reflow. In some muscles the adenosine triphosphate (ATP) levels are also measured. Ischaemia led to a 39% reduction of Cl^– conductance (G _Cl), whereas reperfusion increase G _Cl by 18% with respect to contralateral control muscles. Ischaemia and reperfusion increased K⁺ conductance (G _K) by 21% and 68%, respectively; this increased was reversed by 50 M glybenclamide, suggesting an involvement of ATP-sensitive K⁺ channels. A statistically significant hyperpolarization and increase in excitability was observed after ischaemia, whereas after the reflow period the fibres were depolarized and less excitable. Ischaemia and reperfusion lowered the intracellular ATP content by 18% and 64%, respectively.     

去甲二氢愈创木酸对胶质瘤细胞诱导的内皮细胞迁移的影响

目的 观察去甲二氢愈创木酸（ＮＤＧＡ）对胶质瘤细胞诱导的内皮细胞迁移的影响。方法 采用微孔滤膜培养小室及室细胞联合培养法,进行人脐静脉内皮细胞系ＥＣＶ－３０４细胞与人恶性胶质瘤细胞系ＳＨＧ－４４细胞的联合培养,并以免疫组化ＳＰ方法检测ＳＨＧ－４４细胞血管内皮生长因子（ＶＥＧＦ）、碱性成纤维细胞生长因子（ｂＦＧＦ）的表达。结果 １００μｍｏｌ／Ｌ的ＮＤＧＡ作用１～３ｄ后,ＳＨＧ－４４细胞ＶＥＧＦ、ｂ     

Stretch-activated channels in the basolateral membrane of single proximal cells of frog kidney

Epithelial cells are capable of regulating their volume in response to osmotic swelling or shrinkage. In the present paper a channel is described which may be involved in such a volume-regulatory response. Channels were studied in cell-attached patches of the basolateral membrane of cells isolated from frog kidneys using the patch-clamp technique. The open probability of the channels is increased by the application of negative pressure to the rear of the patch pipette or by bathing the cells in hypotonic fluid. In addition, the channels are voltagesensitive, such that depolarisation increases the open probability. The channels have a conductance of 25 pS with amphibian Ringer as the pipette solution and appear not to discriminate between potassium and sodium. Replacement of chloride by gluconate as the dominant anion in the pipette solution did not affect the current/voltage relationship, suggesting that the channels are cation-nonselective. Inward currents are observed at the resting membrane potential with either potassium or sodium as the dominant cation in the pipette solution: this obviates the channels serving a role as the route for solute exit from the cell during a volume-regulatory decrease response and suggests that they may act as the transduction mechanism sensing changes in cell volume.     

The effect of internal barium on the K current of the node of Ranvier

Voltage clamp experiments were performed on single myelinated nerve fibres of the frogRana esculenta to study the influence of internally applied Ba on the potassium outward current I_K. Potassium currents of Ba-treated fibres decay rapidly during 30 ms depolarizations of more than 60 mV. The time constant of decay and the steady state potassium current I_Kss are strongly voltage dependent. The equilibrium dissociation constant K of the Ba-receptor complex decreases e-fold for a 39 mV change of potential. The analysis suggests that the binding site is located at 30% of the membrane field seen from the inside of the axon.     

The effect of amiloride on the transepithelial potential difference of the distal tubule of the rat kidney

Summary Microelectrodes with relatively large tips (3–5 O.D.) were used to measure the transepithelial potential difference (PD) of the distal tubule of the rat kidney in the control state and following i.v. administration of amiloride. This drug produced an increase in the magnitude of the positive PD in early distal segments (from +8.0 to +10.5 mV) and a change in polarity of the PD in late distal segments (from –18.0 to +2.5 mV). These data suggest that the potassium-conserving properties of the drug are due to its ability to induce an unfavorable electrochemical gradient opposing passive potassium secretion along the distal tubule.     

FOS蛋白在胶质瘤中的表达及其对胶质瘤细胞生长的影响

目的 探讨FOS蛋白在胶质瘤中的表达及其对胶质瘤细胞生长的影响.方法 用免疫组化染色法检测FOS蛋白在各级别胶质瘤组织中的表达水平.应用RNA干扰技术降低FOS表达后,应用四甲基偶氮唑盐微量酶反应比色法和流式细胞技术检测胶质瘤细胞的增殖和周期的改变;应用Transwell实验检测胶质瘤细胞侵袭能力的改变;采用Western印迹法检测FOS下游功能蛋白的变化.结果 胶质瘤组织中FOS的表达随着级别的增高而增高;抑制FOS的表达后,U87和U251细胞生长受抑制,细胞生长阻滞在G1期且细胞侵袭能力下降,下游的功能蛋白CyclinD1和MMP9表达水平降低.结论 FOS在胶质瘤中高表达;抑制其表达可以下调功能蛋白CyclinD1和MMP9的表达,进而调控细胞的生长和侵袭能力.