Enhancement by veratridine and 60 mM KCl of vasopressin-induced 3',5'-cyclic adenosine monophosphate production and cellular free calcium concentration in rat renal papillary collecting tubule cells in culture.

The effect of extracellular calcium (Ca2+) on the cellular action of arginine vasopressin (AVP) was examined using depolarizing agents in rat renal papillary collecting tubule cells in culture. One-hour exposure of cells to veratridine enhanced AVP-induced cAMP production in a dose-dependent manner. This enhancement by veratridine of cellular cAMP production in response to AVP was totally blunted by cotreatment with 5 X 10(-4) M verapamil, 3 X 10(-3) M cobalt, or Ca2+-free medium containing 1 X 10(-3) M EGTA. These agents block cellular Ca2+ uptake by different mechanisms. Similarly, 60 mM KCl enhanced AVP-induced cAMP production, and this effect was blocked by pretreatment with verapamil, cobalt or Ca2+-free medium containing 1 X 10(-3) M EGTA. When cellular free Ca2+ concentrations [Ca2+]i were measured by the fluorescence dye fura-2, both 1 X 10(-4) M veratridine and 60 mM KCl significantly increased [Ca2+]i from 67.6 to 141.8 nM and from 74.6 to 166.2 nM, respectively. Such rises in [Ca2+]i depended on extracellular Ca2+ since the increase in [Ca2+]i was completely blocked in Ca2+-free medium or in the presence of 3 X 10(-3) M cobalt. In addition, veratridine and 60 mM KCl significantly augmented the AVP-induced increase in [Ca2+]i. The possible mechanisms by which depolarizing agents induce cellular Ca2+ mobilization include the opening of voltage-sensitive Ca2+ channels in the plasma membrane. The present results indicate that veratridine and 60 mM KCl enhance AVP-induced cAMP production and cellular free Ca2+ concentration through cellular Ca2+ uptake in renal papillary collecting tubule.