Ionic conductances of cultured principal cell epithelium of renal collecting duct

The ionic conductive properties were studied of epithelia of collecting duct principal cells which had been grown in primary tissue culture from renal cortex/capsule explants. When pretreated with aldosterone (10^–6 mol/l) and bathed on either surface with isotonic HCO ₃ ^– -free Ringer's solution, the transepithelial voltage,V _te, varied between –21 and –72 mV (apical surface negative) while the transepithelial resistance,R _te, ranged from 0.4 to 1.5 kcm². By 10:1 step-changes in Na⁺ concentration the apical cell membrane was shown to have a high conductivity for sodium, inhibitable by amiloride, 10^–6 mol/l. However, contrary to observations in natural collecting duct under control conditions, amiloride never reversed the polarity ofV _te even at 10^–4 mol/l. Both the apical and the basolateral cell membranes were conductive for potassium and both conductivities were inhibitable by Ba²⁺ (5 mmol/l). 10:1 reduction of apical Cl^– concentration strongly hyperpolarizedV _te with a monophasic time course suggesting the presence of a paracellular shunt conductance for Cl^–. In addition there may be a small Cl^– conductance present in the apical cell membrane since apical application of the chloride channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPAB) at 10^–7 mol/l produced a minute but significant hyperpolarization. On the other hand, 10:1 reduction of basolateral Cl^– concentration caused a biphasic change inV _te (initial depolarization, followed by repolarization) which indicates the presence of a large Cl^– conductance in the basolateral cell membrane. The latter was not inhibitable by 10^–7 mol/l NPPAB. Higher concentrations of this and of an other Cl^– channel blocker produced non-specific effects. In conclusion, our studies of a pure principal cell epithelium confirm findings described for the intact cortical collecting duct and add new information concerning chloride conductivity and related blocking agents.Dedicated to Prof. Dr. H. Sitte, Homburg, FRG, upon his 60th birthday.     

Fast network oscillations in the rat dentate gyrus in vitro

The dentate gyrus is a prominent source of gamma frequency activity in the hippocampal formation in vivo. Here we show that transient epochs of gamma frequency network activity (67 +/- 12 Hz) can be generated in the dentate gyrus of rat hippocampal slices, following brief pressure ejections of a high-molarity potassium solution onto the molecular layer. Oscillatory activity remains synchronized over distances >300 microm and is accompanied by a modest rise in [K(+)](o). Gamma frequency oscillations were abolished by a GABA(A) receptor antagonist demonstrating their dependence on rhythmic inhibition. However, in many cases, higher frequency oscillations (>80 Hz) remained in the absence of synaptic transmission, thus demonstrating that nonsynaptic factors may underlie fast oscillatory activity.     

Über das regelmässige Vorkommen von Lipoproteiden im Harn des Gesunden

Journal of Molecular Medicine - Der Urin des Gesunden enthält regelmäßig kleine Mengen Eiweiß, die mit den üblichen Eiweißproben nicht nachweisbar sind. Es setzt sich,...     

Iduronate-2-sulfatase gene mutations in 16 patients with mucopolysaccharidosis type II (Hunter syndrome)

Mutations of the iduronate-2-sulfatase gene were identifiedin 16 patients with mucopolysaccharidosis type II (Hunter syndrome).Together with another 10 cases reported by us earlier it emergesthat about 20% of the patients have deletions of the whole geneor other major structural alterations. One, two or three basepair deletions are found in about 23% of the cases while theremaining about 57% carry point mutations predicting amlno acidreplacement, premature termination of translation, or aberrantsplicing. Molecular analysis of mRNA in splice site mutantsshowed that these latter defects frequently resulted in useof cryptic splice sites in exons or introns. 62% of the smalldeletions and point mutations have occurred in 3 of the 9 iduronate-2-sulfatasegene exons. Knowledge of the primary genetic defect allows fastand reliable carrier detection and prenatal diagnosis as wellas insight into the relationship between genotype and phenotype.     

The response of hepatic angiotensinogen secretion to experimental inflammatory stimuli

Angiotensinogen is thought to be an acute-phase protein, since its plasma concentrations increase in response to some inflammatory conditions, e.g. partial hepatectomy, nephrectomy or lipopolysaccharide (LPS) injection. However, this response of angiotensinogen has never been related to that of established acute-phase proteins. We have, therefore, examined plasma concentrations and hepatic secretion of angiotensinogen in two widely used inflammation models, i.e. turpentine or LPS injection in the rat, as well as in nephrectomized and sham-nephrectomized rats, in comparison to the response of two established acute-phase proteins, ₁-acid glycoprotein (AGP) and ₁-macroglobulin (AMG). Plasma concentrations and secretion rates of AGP and AMG increased significantly in all the conditions examined. The magnitude of the response decreased in the order turpentine > nephrectomy = LPS > sham nephrectomy. Angiotensinogen secretion was stimulated in LPS-injected (2.5-fold) and nephrectomized rats (2.6-fold), whereas no changes were seen in sham-nephrectomized rats. Surprisingly, a significant decrease both in secretion rates and plasma concentrations of angiotensinogen occurred in turpentine-injected rats.Intraperitoneal injection of interleukin 6, a major inductor of hepatic acute-phase proteins, increased plasma concentrations and hepatic secretion rates of AGP, AMG and angiotensinogen. Changes in liver angiotensinogen mRNA correlated well with angiotensinogen secretion rates in all groups, indicating that alterations in angiotensinogen synthesis are responsible for the observed changes in secretion rates and plasma concentrations. The response of angiotensinogen to turpentine is difficult to reconcile with the conventional definition of an acute-phase protein.     

Regulation of organic cation transport

Transport of organic cations (OC) is important for the recycling of endogenous OC and also a necessary step for detoxification of exogenous OC in the body. Even though the identification and characterisation of numerous OC transporters in recent years has allowed the elucidation of molecular mechanisms underlying OC transport, elucidation of the regulation of this transport is just beginning. This review summarises the general properties of OC transport and then analyses the literature on the regulation of these processes. Studies on short- and long-term regulation of OC transport are considered separately. Important aspects of short-term regulation have been clarified and the regulatory pathways of several OC transporters have been characterised. Short-term regulation appears to be transporter subtype-, tissue- and species-dependent and to involve transporter phosphorylation. Transporter phosphorylation may alter the affinity for substrates or/and expression on the plasma membrane. Even though several studies have shown long-term regulation of OC transport, the pathophysiological meaning of these changes are not well understood. In this case, regulation seems to be subtype-, tissue- and gender-specific. Further research is necessary to clarify this important issue of regulation of OC transport.     

Bloom''s Syndrome. VII. Progress report for 1978

The Bloom's Syndrome Registry was published in this journal in 1977. Now, in the first in a series of progress reports, recent accessions to the Registry are recorded, new instances of neoplasia are listed, and recent clinical observations and experimental results of general interest are cited.     

Effect of various diuretics on membrane voltage of macula densa cells. Whole-cell patch-clamp experiments

The tubuloglomerular feedback mechanism is inhibited by diuretics such as furosemide. For the macula densa (MD) cells similar transport systems, as present in thick ascending limb (TAL) cells, have been suggested. To examine this further, membrane voltages (V _m) of MD cells were recorded with the fast or slow wholecell patch-clamp method. The effects of diuretics on voltages and the conductance properties of these cells were examined. V _m of MD cells measured with the whole-cell patch-clamp method were as high as those in TAL cells: –72±1 mV (n=21). An increase in the extracellular K⁺ concentration by 15 mmol/l depolarized V _m of MD cells by 11±1 mV (n=18). Ba²⁺ (1 mmol/ l) reversibly depolarized MD cells by 10±2 mV (n= 10). Thus, MD cells possess a K⁺ conductance that could allow for the recycling of K⁺ taken up by the Na⁺-2 Cl^–-K⁺ cotransporter. MD cells hyperpolarized reversibly upon addition of the loop diuretics furosemide, piretanide and torasemide, whereas muzolimine and hydrochlorothiazide, neither one acting on this cotransport system in other preparations including the TAL, had no effect on V _m. MD cells most likely possess the same cotransport system as the TAL cells, which drives NaCl reabsorption in the TAL and serves as sensor for the tubular NaCl concentration in MD cells.