A voltage-dependent ionic channel in the basolateral membrane of late proximal tubules of the rabbit kidney

Abstract

The patch-clamp method was applied to the lateral membrane of late proximal tubules of the rabbit kidney. Tubule segments were cannulated on one side by a perfusion system. At the noncannulated end of the tubules, the lateral membrane was accessible to a patch pipette. In cell-attached, as well as cell-excised (presumably inside-out oriented) membrane patches, a voltage sensitive channel was observed. The open-state probability of this channel increased with depolarizing potentials. In cell-excised patches bathed with NaCl-Ringer on both sides, the single channel conductance g was 28.0 +/- 1.2 pS (n = 10). With KCl-Ringer in the pipette and NaCl-Ringer in the bath g was 24.7 +/- 1.3 pS (n = 7) and the current-voltage curve crossed the axis at 0 mV. Therefore, the channel does not discriminate between K+ and Na+ ions. Replacing half of NaCl by mannitol on the bath side yielded a permeability for cations about twice as high as for Cl-. The channel could be reversibly blocked by diphenylamine-2-carboxylate (DPC), whereas its inhibition by SITS was only partially reversible. In cell-attached patches, the channel was nearly inactivated at zero clamp potential, but became active when the membrane patch was depolarized. The significance of this nonselective channel for proximal tubule cell function is still unclear. It could be involved in the contraluminal exit mechanism of various anions. However, it could also play a role in cell volume regulation processes.

A Cl- channel activated by parathyroid hormone in rabbit renal proximal tubule cells.

“…Therefore, the basolateral membrane of the PCT is the only side capable of being patch clamped. Available data in cell-attached patch studies indicate that there is only a nonspecific Cl-permeable cation channel in the basolateral cut-end of rabbit proximal tubules (2). Thus a Cl--specific channel may not exist in the basolateral membrane.…”

“…On the other hand, fluid-secreting epithelia possess an apical CP-channel to secrete this anion (1). Although the presence ofthe basolateral Cl-route has been suggested in many fluid-reabsorbing epithelia, available data by patch clamp analysis have suggested the absence of an anion selective channel in the basolateral membrane of rabbit proximal convoluted tubules (PCT)' (2). Rather, a C1-channel is found in the basolateral membrane of renal distal tubules (3) and in a number ofcultured epithelia on their apical membrane (4)(5)(6)(7)(8).…”

Mouse cortical collecting duct cells show nonselective cation channel activity and express a gene related to the cGMP-gated rod photoreceptor channel.

“…The presence of renal mRNA that hybridized to a retinal cGMP-gated channel probe is of interest, since nonselective cation channels have been detected electrophysiologically in the proximal tubule (9,10), in cortical thick ascending limb cells (11), and in collecting duct cells (12)(13)(14). Furthermore, cGMP seems to play a role in the regulation ofthe nonselective cation channel in the inner medullary collecting duct (15,16).…”

Potassium channels in basolateral membrane vesicles from pars convoluta of rabbit proximal tubule

“…The present findings on the influence of intravesicular Ca2 + are in contrast to what was found for basolateral K + channels in rabbit proximal straight tubule (pars recta). These were reported not to be directly dependent on Ca2 + ions [19,20]. Neither K+ channels in basolateral membrane of Necturus proximal tubule were affected by cytosolic side Ca2 + in a concentration of 3 mM [21].…”