Membrane crosstalk in the mammalian proximal tubule during alterations in transepithelial sodium transport.

Academic Article

Abstract

  • The present paper examines the effects of reduced transepithelial Na transport (JNa) on membrane electrophysiological parameters in proximal convoluted tubules and the possible role of cytosolic calcium concentration ([Ca]i) in the regulation of basolateral membrane K conductance (GK). When JNa was reduced by elimination of glucose and alanine and replacement of 100 mM sodium with N-methyl-D-glucamine from the luminal perfusate, basolateral membrane potential (VBL) hyperpolarized transiently by 12.6 mV and the ratio of apical to basolateral membrane resistance (RA/RBL) doubled. The apparent transference number for K at the basolateral membrane (GK/Gcell) decreased from 0.13 to 0.08 in the first 4 min following reductions in JNa. The elimination of Na-alanine and Na-glucose cotransport was responsible for the initial hyperpolarization and increase in RA/RBL, whereas the resultant decrease in the cellular concentrations of glucose and alanine, together with the reductions in GK, could elicit the secondary VBL depolarization. Measurement of [Ca]i with the fluorescent probe fura-2 during reductions in JNa revealed that [Ca]i increased by an average of 12%, a value very similar to the average reduction in cellular volume (13%) measured using morphometric techniques. The observation that [Ca]i increased while GK was decreasing is inconsistent with the effect of [Ca]i on putative basolateral Ca-activated K channel. We believe that [Ca]i changes passively (at least in the first few minutes) in response to a decrease in cell volume occurring as a consequence of reductions in JNa and that some as yet unidentified volume-sensitive mechanism is responsible for the regulation of GK.
  • Authors

    Published In

    Keywords

  • Animals, Biological Transport, Calcium, Electrophysiology, Epithelium, Kidney Tubules, Proximal, Membrane Potentials, Osmolar Concentration, Potassium, Rabbits, Sodium, Time Factors
  • Digital Object Identifier (doi)

    Author List

  • Lapointe JY; Garneau L; Bell PD; Cardinal J
  • Start Page

  • F339
  • End Page

  • F345
  • Volume

  • 258
  • Issue

  • 2 Pt 2