Search PubMed⌕ Search

Biomedical subjects

H Völkl

Publications and source records attributed to H Völkl.

At least 19 recordsLinked to original sources
PubMed1994

Involvement of microtubules in the link between cell volume and pH of acidic cellular compartments in rat and human hepatocytes.

Cell swelling is shown to induce an increase in acridine orange fluorescence intensity, an effect pointing to the alkalinization of acidic vesicles. Since autophagic hepatic proteolysis is accomplished by pH-sensitive proteinases within acidic lysosomes, this effect may contribute to the well-known inhibitory effect of cell swelling on proteolysis. In the present study, the role of microtubules in volume-dependent alterations of pH in acidic vesicles of rat and human hepatocytes was studied. Colcemid and colchicine were used to depolymerize microtubules and vesicular pH was monitored using two different fluorescent dyes, fluorescein isothiocyanate conjugated-dextran and acridine orange. Colcemid and colchicine, but not the inactive stereoisomer gamma-lumicolchicine, blunted the increase of pH during osmotic cell swelling. The alkalinization of acidic vesicles by NH4Cl was not significantly modified by colcemid or colchicine, indicating that the vesicles were still sensitive to alkalinizing procedures other than cell swelling. Further, colchicine, but not gamma-lumicolchicine, inhibited the antiproteolytic action of osmotic cell swelling. The present observations point to an involvement of the microtubule network in the link of cell volume, lysosomal pH, and proteolysis.

Animals↗
PubMed1994

Alkalinization of acidic cellular compartments following cell swelling.

Osmotic swelling of rat hepatocytes increases fluorescence of Acridine orange and of fluorescein isothiocyanate (FITC)-dextran, both indicative of alkalinization of acidic intracellular vesicles. Similar to osmotic cell swelling, insulin and glutamine lead to an increase in Acridine orange fluorescence, an effect virtually abolished upon osmotic reversal of glutamine-induced cell swelling. Barium, which blocks K+ channels in the plasma membrane, similarly leads to cell swelling and increase of Acridine orange fluorescence. Since proteolysis is governed by lysosomal pH, these observations indicate that the anti-proteolytic action of osmotic cell swelling is mediated by lysosomal alkalinization. Thereby, insulin, glutamine and barium probably exert their anti-proteolytic action by cell swelling and subsequent lysosomal alkalinization.

Acridine Orange↗
PubMed1994

Regulation of proximal renal tubular K+ conductance by intracellular pH.

Conventional electrophysiology and 2', 7'-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein fluorescence have been applied to elucidate the effects of metabolic acidosis on straight proximal tubules of the mouse kidney. Reduction of extracellular bicarbonate concentration from 20 to 10 mmol/l leads to a decline of intracellular pH from 7.00 +/- 0.06 to 6.85 +/- 0.05, a depolarization of the cell membrane (PDbl) from -72 +/- 1 to -59 +/- 2 mV, a decrease of the basolateral transference number for potassium (tK) from 0.80 +/- 0.01 to 0.54 +/- 0.03, an increase of the basolateral transference number for bicarbonate (tb) from 0.16 +/- 0.02 to 0.42 +/- 0.03 and an increase of the fractional resistance of the basolateral over the luminal cell membrane (Rb/Ra) by 64 +/- 8%. Upon return to 20 mmol/l bicarbonate after a 5-min exposure to 10 mmol/l bicarbonate, the intracellular pH approached a more alkaline value (7.28 +/- 0.08) than before exposure to acidosis. Despite the intracellular alkalosis, PDbl (-67 +/- 1 mV) and tK (0.73 +/- 0.02) remained significantly below, and tb (0.26 +/- 0.02) and Rb/Ra (32 +/- 8%) significantly above the respective values before induction of acidosis. Even transient exposure of the tubules to 40 mmol/l extracellular bicarbonate did not restore the original electrophysiological properties of the tubule cells. It is concluded that both a rapidly reversible and a long-lasting decrease of proximal tubular K+ conductance follows cellular acidosis.

Acidosis↗
PubMed1994

Maitotoxin activates a nonselective cation channel and stimulates Ca2+ entry in MDCK renal epithelial cells.

We examined the mechanisms of maitotoxin (MTX), a water-soluble polyether from the marine dinoflagellate Gambierdiscus toxicus, in stimulation of Ca2+ entry into Mardin-Darby canine kidney cells. In the presence of bath Ca2+, MTX (3 nM) caused an elevation of the intracellular calcium concentration ([Ca2+]i), which was partially inhibited by SK&F 96365 (25 microM) or La3+ (100 microM). A stimulation of Ca(2+)-dependent K+ channels in cell-attached membrane patches coincided with this rise in [Ca2+]i and was also partially inhibited by SK&F 96365. Before the rise in [Ca2+]i, a nonselective cation current (Ins), studied by the whole-cell patch-clamp technique, was irreversibly activated. Ins poorly discriminated between Na+, K+, and Cs+, was unaffected by replacement of Cl- with gluconate-, and was not voltage gated. MTX-induced Ins was partially blocked by La3+ ions (100 microM) but not by SK&F 96365 (25 microM) or nifedipine (10 microM). SK&F 96365 by itself induced a small but significant stimulation of Ins and a rise in [Ca2+]i. The activation of Ins by MTX was instantaneous and depended on the presence of extracellular Ca2+ ions. In the absence of other cations, the inward current of Ins was dependent on the bath Ca2+ concentration. Cell-attached and excised single-channel measurements revealed that MTX activated a SK&F 96365-insensitive, approximately 40-pS, nonselective cation channel from the outside. We conclude that the initial action of MTX is the stimulation of a nonselective cation channel, which requires the presence of extracellular Ca2+ ions. The subsequent rise in [Ca2+]i is at least in part caused by another, SK&F 96365-sensitive, Ca2+ entry pathway, which may be activated as a result of or independently of Ins.

Animals↗
PubMed1991

Hepatorenal reflex regulating kidney function.

In anesthetized male rats, infusion of glutamine (2 mumol/min) into the superior mesenteric vein at a rate known to induce liver cell swelling leads to marked decreases in renal glomerular filtration rate, renal para-aminohippurate clearance and urinary flow rate. Glutamine infused at identical rates into the jugular vein does not elicit any of these effects. The effect of glutamine is mimicked by serine but not by glutamate. Spinal transection, renal denervation or section of the vagal hepatic nerves abolishes the effect of mesenteric venous glutamine infusion. Mesenteric application of glucagon (1 ng/min) or of both glutamine and glucagon enhances glomerular filtration rate and urinary flow rate. Infusion of 1 ng/min glucagon through the jugular vein does not significantly alter glomerular filtration rate or urinary flow rate. The data disclose a powerful liver-borne mechanism regulating kidney function that is mediated by the hepatorenal innervation.

Animals↗
PubMed1991

Electrophysiology of ammonia transport in renal straight proximal tubules.

To test for electrogenic transport of ammonium ions in straight proximal renal tubules, isolated perfused tubules have been exposed to peritubular ammonium ions during continuous recording of cell membrane potential. As a result, 20 mmol/liter NH4+ leads to a rapid, reversible depolarization of the cell membrane by 9.0 +/- 0.3 mV (N = 86). This depolarization is not significantly affected by 10 mmol/liter barium or 0.1 mmol/liter amiloride on both sides of the epithelium, but is significantly blunted by omission of extracellular bicarbonate and CO2 (3.8 +/- 0.4 mV, N = 9), by 1 mmol/liter acetazolamide (4.3 +/- 0.3 mV, N = 11), by 1 mmol/liter peritubular amiloride (4.3 +/- 1.1 mV, N = 7), by 1 mmol/liter SITS (5.7 +/- 0.4 mV, N = 6), and by replacement of extracellular sodium with choline (4.7 +/- 0.5 mV, N = 8). In the presence of both amiloride (1 mmol/liter) and acetazolamide (1 mmol/liter) in the bath, the NH4+ induced depolarization is completely abolished. Furthermore, the combined omission of bicarbonate and addition of 10 mmol/liter barium eliminates the NH4+ induced depolarization. About 50% of the depolarization can be explained by enhanced electrogenic bicarbonate exit due to the intracellular alkalosis. The other 50% is explained by amiloride and barium sensitive electrogenic entry of NH4+ into the cell.

Acetazolamide↗
PubMed1990

Effect of potassium on cell volume regulation in renal straight proximal tubules.

The present study was designed to assess for the influence of extracellular potassium and of inhibitors of potassium transport on cell volume regulatory decrease in isolated perfused straight proximal tubules of the mouse kidney. Volume regulatory decrease is virtually unaffected when bath potassium concentration is elevated from 5 to 20 mmol/liter, and still persists, albeit significantly retarded, in the presence of the potassium channel blocker barium on both sides of the epithelium and during virtually complete dissipation of the transmembrane potassium gradient by increasing extracellular potassium concentration to 40 mmol/liter. As evident from electrophysiologic observations, barium blocks the potassium conductance of the basolateral cell membrane. Reduction of bicarbonate concentration and increase of H+ concentration in the bath solution cannot compensate for enhanced potassium concentration and cell volume regulatory decrease is not affected in the presence of the K/H exchange inhibitor omeprazole. Similarly cell volume regulatory decrease is not affected by ouabain. In conclusion, potassium movements through potassium channels in the basolateral cell membrane are important determinants of cell volume and may participate in cell volume regulatory decrease. However, a powerful component of cell volume regulatory decrease in straight proximal tubules of the mouse kidney is apparently independent of potassium conductive pathways, K/H exchange and Na+/K(+)-ATPase.

Animals↗
PubMed1989

Effect of furosemide, bumetanide and mannitol on intracranial pressure in experimental brain edema of the rat.

Loop diuretics interfere with NaCl-KCl cotransport, which operates not only in the kidney but as well in a variety of nonepithelial cells including neuronal and glial cells. In these cells loop diuretics are able to reduce cellular volume. The present study has been performed to establish, whether furosemide or bumetanide directly modify intracranial pressure in cytotoxic brain edema. To this end, water intoxication was induced in animals acutely nephrectomized, to exclude any consequences of renal effects. Neither furosemide nor bumetanide proved effective in reducing intracranial pressure. In contrast, infusion of hypertonic mannitol solution leads to a marked, rapid reduction of intracranial pressure. The observations rule out a direct action of loop diuretics on intracranial cells to reduce intracranial pressure in water intoxicated animals.

Animals↗
PubMed1989

[Marginal gaps of combined composite and glass ionomer cement fillings in different preparations in vitro].

In 34 extracted molars with class V cavities (coronal margin in the enamel, apical margin in the dentin) a shoulder or a shoulder with bevel were prepared on the apical aspect. The dentin was covered with glass ionomer cement (GIC) and after beveling the neighboring enamel composite material was applied on top with enamel etching. 24 other cavities filled with either composite or glass ionomer cement served as controls. The specimen were exposed to 2000 alternating thermal tests (1 min. at 8 degrees C, 1 min at 60 degrees C) and alternations of the filling margins were recorded quantitatively using replicas in the SEM. After the alternating thermal tests GIC controls showed statistically significant better margin in enamel and dentin with shoulder preparations alone than the combined or pure composite fillings. Combined fillings with beveled apical cavity margins were superior to shoulder preparations alone. Glass ionomer cement seems to be better for the treatment of class V cavities in terms of margin tightness than composite alone or in combination.

Composite Resins↗
PubMed1988

Effect of amiloride on cell volume regulation in renal straight proximal tubules.

Amiloride has been shown to impair cell volume regulatory decrease in amphiuma red cells. The present study has been performed to test for the influence of amiloride on volume regulatory decrease and electrical properties in isolated perfused mouse straight proximal tubules. Replacement of 40 mmol/l NaCl with 80 mmol/l mannitol in bath perfusate does not appreciably affect the cell volume or the potential difference across the basolateral cell membrane. Reduction of osmolarity by omission of mannitol leads to cell swelling by 16.7 +/- 0.7% (n = 7), followed by volume regulatory decrease to 107.2 +/- 1.2% (n = 7) of original cell volume within 2 min. 1 mmol/l amiloride (but not 0.1 mmol/l amiloride) in the bath depolarizes the basolateral cell membrane from -63 +/- 1 mV (n = 24) by +16 +/- 1 mV (n = 16), decreases the apparent potassium transference number from 0.69 +/- 0.02 (n = 5) to 0.36 +/- 0.05 (n = 5), and significantly impairs volume regulatory decrease without appreciably modifying cell volume in isotonic solutions. 1 mmol/l amiloride in the luminal perfusate leads to a slight hyperpolarization of the basolateral cell membrane but does not interfere with volume regulatory decrease. Reduction of bath osmolarity depolarizes the basolateral cell membrane within 30 s by +7.8 +/- 0.8 mV (n = 18) in the absence and by +18 +/- 2 mV (n = 8) in the presence of amiloride. In the presence of reduced bath osmolarity and amiloride the potassium transference number amounts to 0.36 +/- 0.04 (n = 8). The hyperpolarization following luminal application of amiloride is most likely due to inhibition of luminal sodium channels, whereas bath amiloride depolarizes the basolateral cell membrane by reduction of basolateral potassium selectivity. As in amphiuma red cells amiloride impairs volume regulatory decrease in proximal straight renal tubules.

Amiloride↗
PubMed1988

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 (PDbl) 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 PDbl is decreased (delta PDbl = +16 +/- 2 mV, n = 11), the influence of altered bicarbonate concentration on PDbl is increased (delta PDbl = -6.0 +/- 0.8 mV, n = 13), and the influence of altered bath chloride concentration on PDbl is unaffected (delta PDbl = -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).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Ionic requirement for regulatory cell volume decrease in renal straight proximal tubules.

The present study has been performed to test for the ionic requirement of regulatory cell volume decrease in isolated perfused straight proximal tubules of the mouse kidney. Reduction of peritubular osmolarity from 308 mosmol/l to 228 mosmol/l leads within 0.5 min to cell swelling by 16 +/- 1% (n = 26) of original cell volume (Vo). Within 2 min cell volume (V2) approaches 105 +/- 1% of Vo (n = 26) despite continued exposure to hypotonic bath perfusate. Reexposure of the tubules to isotonic bath perfusate shrinks the cells to 94 +/- 1% of Vo (n = 25). Within 2 min from omission of extracellular bicarbonate and CO2 regulatory cell volume decrease is impaired (V2 = 114 +/- 1% of Vo, n = 14). Similarly, regulatory volume decrease is blunted upon prior removal of extracellular sodium (V2 = 115 +/- 2% of Vo, n = 12). In contrast, regulatory volume decrease is not affected by prior removal of extracellular chloride (V2 = 104 +/- 2% of Vo, n = 9). Regulatory volume decrease is impaired in the presence of 1 mmol/l potassium channel blocker barium (V2 = 120 +/- 4% of Vo, n = 7) and of 1 mmol/l carbonic anhydrase inhibitor acetazolamide (V2 = 111 +/- 2% of Vo, n = 16) but is preserved in the presence of 1 mumol/l chloride channel blocker NPPB (V2 = 105 +/- 2% of Vo, n = 11). In conclusion, regulatory cell volume decrease apparently depends on potassium and bicarbonate, but does not depend on chloride.

Animals↗
PubMed1987

Potassium conductance in straight proximal tubule cells of the mouse. Effect of barium, verapamil and quinidine.

The present study has been performed to test for the influence of verapamil and quinidine on the potential difference across the basolateral cell membrane (PDbl) and on the basolateral potassium conductance of isolated perfused segments of the mouse proximal tubule. PDbl was recorded continuously with conventional microelectrodes during rapid alterations of bath or luminal perfusate composition. The contribution of the basolateral potassium conductance to the conductance of both cell membranes (tk) was estimated from the effects of altered bath potassium concentration on PDbl. Under control conditions tk approaches 0.8, i.e. the basolateral cell membrane is mainly conductive to potassium. Neither quinidine nor verapamil affect PDbl at concentrations below 10 mumol/l. At higher concentrations both substances depolarize the basolateral cell membrane mimicking the effect of 1 mmol/l barium. In the presence of 0.1 mmol/l verapamil tk is virtually abolished at 5 to 10 mmol/l bath potassium concentration but is almost unaffected at bath potassium concentrations between 20 and 40 mmol/l. 1 mumol/l ionophore A-23187 does not change the depolarizing effect of 0.1 mmol/l verapamil on cell membrane potential. In the presence of 0.1 mmol/l quinidine, tk is reduced to some 50%, irrespective of the bath potassium concentration. It is concluded that the potassium conductance in straight proximal tubules is inhibited not only by barium but as well by high concentrations of verapamil and quinidine. The effect is probably direct and not related to alterations in the intracellular calcium activity.

Animals↗
PubMed1986

Effects of ouabain and temperature on cell membrane potentials in isolated perfused straight proximal tubules of the mouse kidney.

In isolated perfused segments of the mouse proximal tubule, the potential difference across the basolateral cell membrane (PDbl) was determined with conventional microelectrodes. Under control conditions with symmetrical solutions it amounted to -62 +/- 1 mV (n = 118). The potential difference across the epithelium (PDte) was -1.7 +/- 0.1 mV (n = 45). Transepithelial resistance amounted to 1.82 +/- 0.09 k omega cm (n = 28), corresponding to 11.4 +/- 0.6 omega cm2. Increasing bath potassium concentration from 5 to 20 mmol/l depolarized PDbl by +24 +/- 1 mV (n = 103), and PDte by +1.6 +/- 0.1 mV (n = 19). Thus, the basolateral cell membrane is preferably conductive to potassium. Rapid cooling of the bath perfusate from 38 degrees C to 10 degrees C led to a transient hyperpolarization of PDbl from -60 +/- 1 to -65 +/- 1 mV (n = 21) within 40 s followed by gradual depolarization by +18 +/- 1% (n = 14) within 5 min. The transepithelial resistance increased significantly from 1.78 +/- 0.11 k omega cm to 2.20 +/- 0.21 k omega cm (n = 15). Rapid rewarming of the bath to 38 degrees C caused a depolarization from -61 +/- 2 mV (n = 17) to -43 +/- 2 mV (n = 16) within 15 s followed by a repolarization to -59 +/- 2 mV (n = 10) within 40 s. Ouabain invariably depolarized PDbl. During both, sustained cooling or application of ouabain, the sensitivity of PDbl to bath potassium concentration decreased in parallel to PDbl pointing to a gradual decrease of potassium conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗