title: Membrane crosstalk in the mammalian proximal tubule during alterations in transepithelial sodium transport.
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.affiliation: Groupe de Recherche en Transport Membranaire, Université de Montréal, Québec, Canada.
authors.forename: J Y
authors.initials: JY
authors.lastname: Lapointe
authors.forename: L
authors.initials: L
authors.lastname: Garneau
authors.forename: P D
authors.initials: PD
authors.lastname: Bell
authors.forename: J
authors.initials: J
authors.lastname: Cardinal
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D004848:Epithelium / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials; D009994:Osmolar Concentration; D011188:Potassium / Q000502:physiology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
chemical_list: D012964:Sodium; D011188:Potassium; D002118:Calcium