Luminal vasopressin modulates transport in the rabbit cortical collecting duct

Abstract

We explored the action of luminal AVP in rabbit CCD perfused in vitro at 37°C. Nanomolar concentrations of luminal AVP induced a sustained hyperpolarization of transepithelial voltage (Vt) in contrast to a transient hyperpolarization caused by basolateral AVP. 10 μM basolateral ouabain abolished the latter but not the former change in Vt. Despite a sustained hyperpolarization (from -20.7±2.9 to -34.1±4.7 mV; P < 0.01), 10 nM luminal AVP only slightly altered net Na+ and K+ fluxes (7.6% stimulation and no significant change, respectively). Instead, luminal AVP appeared to modulate an acetazolamide-sensitive electrogenic ion transport because 200 μM basolateral acetazolamide suppressed the luminal AVP-induced hyperpolarization (percentage of Vt from -50.4±10.8 to -5.1±1.4; P < 0.005). In terms of water transport, 10 nM luminal AVP did not change hydraulic conductivity (Lp, ×10-7 cm/atm per s) (from 3.9±0.8 to 5.0±1.2), but suppressed the increase in Lp induced by 20 pM basolateral AVP (134.9±19.2 vs. 204.3±21.1 in control; P < 0.05). These findings demonstrate distinct luminal action of AVP, suggesting amphilateral regulation of epithelial transport by AVP in the CCD.