Hypotonicity activates a lanthanide-sensitive pathway for K+ release in A6 epithelia.
The nature of the pathway for K+ release activated during regulatory volume decrease (RVD) in A6 epithelia was investigated by measuring cell thickness (Tc) as an index of cell volume and by probing K+ efflux with 86Rb as tracer for K+ (RRb). Cell swelling was induced by sudden reduction of basolateral osmolality (from 260 to 140 mosmol/kgH2O). Experiments were performed in the absence of Na+ transport. Apical RRb was negligible in iso- and hyposmotic conditions. On the other hand, osmotic shock increased basolateral RRb (RblRb) rapidly, reaching a maximum 7 min after the peak in Tc. Quinine (0.5 mM) completely inhibited RVD and RblRb. Also verapamil (0.2 mM) impeded volume recovery considerably; lidocaine (0.2 mM) did not exert a noticeable effect. The K+ channel blocker Ba2+ (30 mM) delayed RVD but could not prevent complete volume recovery. Cs+ inhibited RVD noticeably at concentrations <40 mM. With large Cs+ concentrations (>40 mM), the initial osmometric swelling was followed by a gradual increase of Tc, suggesting activation of Cs+ influx. Chronic exposure of the basolateral surface to 0.5 mM La3+ or Gd3+ completely abolished RVD and RblRb. Acute administration of lanthanides at the time of osmolality decrease did not affect the initial phase of RVD and reduced RblRb only slightly. Apical Gd3+ exerted an inhibitory effect on RVD and RblRb. The effect of Gd3+ should therefore be localized at an intracellular site. The role of Ca2+ entry could be excluded by failure of extracellular Ca2+ removal to inhibit volume recovery. In contrast to lanthanides, chronically and acutely administered Mg2+ (0.5 mM) inhibited RVD and RblRb by approximately 50%. These data suggest that K+ excretion during RVD occurs through a rather poorly selective pathway that does not seem to be directly activated by membrane stretch.
Laboratory of Physiology, Katholieke Universiteit Leuven, Campus Gasthuisberg, B-3000 Louvain, Belgium.
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De Smet
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Li
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Van Driessche
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002412:Cations; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002586:Cesium / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology*; D005682:Gadolinium / Q000494:pharmacology*; D007038:Hypotonic Solutions; D007668:Kidney; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology*; D008012:Lidocaine / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011803:Quinine / Q000494:pharmacology; D012414:Rubidium Radioisotopes / Q000493:pharmacokinetics; D014700:Verapamil / Q000494:pharmacology
D002412:Cations; D007038:Hypotonic Solutions; D015221:Potassium Channels; D012414:Rubidium Radioisotopes; D002586:Cesium; D007811:Lanthanum; D008012:Lidocaine; D011803:Quinine; D005682:Gadolinium; D014700:Verapamil; D008274:Magnesium; D011188:Potassium; D002118:Calcium