Calcium modulates vasopressin effect in rabbit cortical collecting tubule

Abstract

The calcium ion has been proposed to be an important mediator of the hydroosmotic response to arginine vasopressin (AVP). We examined the effect of reducing basolateral calcium activity on hydraulic conductivity (Lp) in response to AVP in rabbit cortical collecting tubules (CCT) perfused in vitro. Each tubule served as its own control. Reducing bathing fluid calcium from 0.94 mM to 4.6 microM reduced Lp in each tubule (mean decrease from 146 +/- 13 to 106 +/- 7 cm X s-1 X atm X 10(-7), n = 11, P less than 0.025). To determine whether this inhibitory effect was due to a decrease in cellular calcium uptake, we measured the effect of adding 10(-4) M lanthanum to bathing fluid on AVP-stimulated Lp. Lanthanum decreased Lp (from 109 +/- 13 to 80 +/- 10 cm X s-1 X atm X 10(-7), P less than 0.05) in each tubule. To examine the site at which low peritubular calcium activity regulates AVP action, we measured the effect of decreasing bathing fluid calcium on 8-[p-chlorophenylthio]-adenosine 3',5'-cyclic monophosphate (ClPheS-cAMP)-stimulated Lp (n = 5). Decreasing bathing fluid calcium significantly decreases (P less than 0.025) Lp response to ClPheS-cAMP. Since these results suggest that cellular calcium uptake can exert a post-cAMP effect to modulate AVP action, we examined the effect of the calcium ionophore A23187 (10(-7) M) on AVP- and ClPheS-cAMP-stimulated Lp A23187 reversibly potentiates (25-30%, P less than 0.025) the Lp response to both AVP and ClPheS-cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)