Signaling path of the action of AVP on distal K+ secretion.

Background: Previous studies from our laboratory have shown that luminal perfusion with arginine vasopressin (AVP) stimulates distal tubule secretory potassium flux (JK) via V1 receptors (Am J Physiol 278:F809-F816, 2000). In the present work, we investigate the cell signaling mechanism of this process.

Methods: In vivo stationary microperfusion was performed in rat cortical distal tubules and luminal K+ was measured using double K+ resin/reference microelectrodes.

Results: In control conditions, JK was 0.71 +/- 0.05 nmol.cm(-2).second(-1); this process was inhibited (14%) by 10(-5) mol/L 8-bromo-cyclic adenosine monophosphate (cAMP), and increased by 35% with 10(-8) mol/L phorbol ester [phorbol12-myristate 13-acetate (PMA), which activates protein kinase C (PKC)]. During luminal perfusion with 10(-11) mol/L AVP, JK increased to 0.88 +/- 0.08 nmol.cm(-2).seconds(-1). In the presence of 10(-11) mol/L AVP, JK was not affected by 10(-4) mol/L H89, a blocker of protein kinase A (PKA), but was inhibited (45%) by 10(-5) mol/L staurosporine, an inhibitor of PKC, and by 41% during perfusion with 5 x 10(-5) mol/L of the cell Ca2+ chelator bis (2-aminophenoxy) ethane-tetraacetic acid (BAPTA). In order to study the role of Ca(2+)-dependent K channels in the luminal hormonal action, the tubules were perfused with 5 mmol/L tetraethylammonium chloride (TEA) or 10(-7) mol/L iberiotoxin, in the presence of AVP, and JK was significantly reduced by both agents. Iberiotoxin reduced AVP-stimulated JK by 36.4%, and AVP-independent JK (after blocking V1 receptors) by only 16%.

Conclusion: The results suggest that the luminal V1-receptor effect of AVP on JK was mediated by the phospholipase C (PLC)/Ca2+/PKC signaling path and not byadenylate cyclase/cAMP/PKA, therefore probably acting on maxi-potassium channels.