AVP reduces transepithelial resistance across IMCD cell monolayers.

The inner medullary collecting duct (IMCD) is an important site of action for arginine vasopressin (AVP). To examine the mode of action of AVP in this segment, we measured the change in transepithelial resistance of cultured rat IMCD cells grown to confluence on collagen-coated Millicell culture plate inserts in response to AVP. Resistance was measured by use of an EVOM voltage-ohm meter. AVP at 10(-11)-10(-8) M caused a fall in resistance of 6.9 +/- 1.3 to 14.0 +/- 1.4 omega.cm2 (P less than 0.05 to less than 0.01 vs. no AVP), which was reversed by removal of AVP or addition of 10(-6) M amiloride. Pretreating the apical surface of IMCD cells with trypsin had no effect on resistance but totally prevented the antidiuretic hormone-induced fall in resistance. Pretreating the apical surface with trypsin and amiloride did not prevent the fall in resistance to AVP. Addition of 10(-9) M AVP or 10(-6) M forskolin increased 2-min adenosine 3',5'-cyclic monophosphate (cAMP) accumulation by 55 or 96%, respectively. Stimulation of endogenous cAMP accumulation by forskolin or the addition of exogenous 8-bromo-cAMP caused no change in resistance. To examine the relationship between intracellular calcium [( Ca2+]i) and AVP action, the response of [Ca2+]i to AVP was measured by use of fura-2. AVP induced no change in [Ca2+]i in IMCD cells in suspension, on glass cover slips, or on permeable supports. Ionomycin (25 nM) increased [Ca2+]i in IMCD cells and lowered resistance across monolayers, but the fall in resistance was not blocked by amiloride.(ABSTRACT TRUNCATED AT 250 WORDS)