Vasopressin stimulates Cl^- transport in ascending thin limb of Henle's loop in hamster

The effect of arginine vasopressin (AVP) on NaCl transport was investigated in the isolated microperfused hamster ascending thin limb of Henle's loop by measuring transepithelial voltage (Vt) and transmural ²²Na⁺ and ³⁶Cl^- fluxes. In the presence of a transmural NaCl concentration gradient (100 mM higher in the lumen), Vt was 8.4±0.4 mV. Addition of 1 nM AVP to the basolateral solution increased Vt to 9.6±0.4 mV, which corresponds to an increase in the Cl^- to Na⁺ permselectivity ratio (P(Cl)/P(Na)) from 2.8±0.2 to 3.4±0.2. AVP at physiological concentrations increased Vt in a dose-dependent manner with an ED₅₀ of 5 pM. AVP increased the Cl^- efflux coefficient from 99.6±6.3 to 131.4±10.6 x 10^-7 cm²/s without affecting the Na⁺ efflux coefficient. 5-Nitro-2-(3-phenyl- propylamino)-benzoate (0.2 mM), a Cl^- channel inhibitor, in the perfusate decreased the basal Cl^- efflux coefficient and inhibited the AVP-induced increase in this parameter. The AVP-induced increase in Vt was not affected by [d(CH₂)₅¹,O-Me-Tyr²,Arg⁸] vasopressin, a V1 receptor antagonist, but was abolished by [d(CH₂)₅,D-Ile²,Ile⁴,Arg⁸] vasopressin, a V2 receptor antagonist. The selective V2 agonist dDAVP in 1 nM also increased Vt from 8.6±0.7 to 9.5±0.6 mV. Dibutyryl cAMP and forskolin both increased Vt, whereas H89, an inhibitor of cAMP-dependent protein kinase, abolished the AVP-induced increase in Vt. These results demonstrate that AVP stimulates Cl^- transport in the ascending thin limb of Henle's loop by activating Cl^- channels via a signal transduction cascade comprising V2 receptors, adenylate cyclase, and cAMP-dependent protein kinase. The ascending thin limb of Henle's loop thus participates in the formation of concentrated urine as one of the target renal tubular segments of AVP.