LUMINAL VASOPRESSIN MODULATES TRANSPORT IN THE RABBIT CORTICAL COLLECTING DUCT

We explored the action of luminal AVP in rabbit CCD perfused in vitro at 37-degrees-C. Nanomolar concentrations of luminal AVP induced a sustained hyperpolarization of transepithelial voltage (V(t)) in contrast to a transient hyperpolarization caused by basolateral AVP. 10-mu-M basolateral ouabain abolished the latter but not the former change in V(t). 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-mu-M basolateral acetazolamide suppressed the luminal AVP-induced hyperpolarization (percentage of V(t) 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 (L(p), X 10(-7) cm/atm per s) (from 3.9 +/- 0.8 to 5.0 +/- 1.2), but suppressed the increase in L(p) 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.