Prompt Inhibition of Arginine Vasopressin-Induced Cellular Adenosine 3′,5′-Monophosphate Production by Extracellular Sodium Depletion in Rat Renal Inner Medullary Collecting Duct Cells in Culture*

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Abstract
The present study was undertaken to determine whether the absence of extracellular Na+ affects cellular action of arginine vasopressin (AVP) in rat renal inner medullary collecting duct cells in culture. AVP increased cellular cAMP production in a dose-dependent manner. Na+ depletion promptly diminished the cellular cAMP response to AVP (1 nM AVP; 405.9 .+-. 26.1 vs. 189.8 .+-. 12.1 fmol/.mu.g protein, P < 0.01). The dose-response relation shifted to the right. The inhibition of the ability of AVP to produce cAMP was observed with an extracellular Na+ concentration less than 60 mM. Similar results were obtained with 2 .times. 10-8 M forskolin, a diterpene activator of adenylate cyclase. Such inhibition was easily released, since only 10-min reexposure of the Na+-depleted cells to the control medium totally recovered the cAMP response to AVP. Extracellular Na+ depletion promptly decreased the cellular Na+ concentration from 15.8 .+-. 1.0 to 5.4 .+-. 0.6 mM (P < 0.01), measured using the fluorescence dye sodium-binding benzofuran isophthalate. If the Na+-depleted cells were again incubated with the control medium, intracellular Na+ rapidly recovered to the precontrol level. Such a change was closely related to the change in cellular pH, which decreased from 7.19 .+-. 0.02 to 6.97 .+-. 0.02, measured using the fluorescence dye 2'',7''-bis-(2-carboxymethyl)-5 (and - 6)carboxyfluorescein, acetamethylester. However, Na+ depletion did not affect the cellular free calcium concentration or cellular protein and ATP contents. These results indicate that Na+ depletion promptly attenuated the ability of AVP to produce cAMP mediated through either the decrease in intracellular Na+ or cellular pH in renal inner medullary collecting duct cells.