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SE Ishikawa, K Okada and T Saito
Department of Medicine, Jichi Medical School, Tochigi, Japan.
The present study was undertaken to determine whether endoplasmic reticulum is involved in the cellular action of arginine vasopressin (AVP) in rat renal papillary collecting tubule cells in culture, using three dissimilar agents. 1 x 10(-7) M AVP increased cytosolic free Ca++ concentration ([Ca++]i) from 93.2 to 188.6 nM (P < .01). Exposure to 1 x 10(-4) M 3, 4, 5-trimethoxybenzoic acid, 8-(diethylamino) octylester hydrochloride (TMB-8), which inhibits intracellular Ca++ mobilization and blocks the function of endoplasmic reticulum, attenuated the [Ca++]i response to AVP. A significant increase in [Ca++]i in response to 1 x 10(-7) M AVP was obtained with Ca(++)-free medium containing 1 x 10(-4) M ethylene glycol bis(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA) (52.3 to 98.3 nM). However, when cells were preincubated with Ca(++)-free medium containing a mixture of 1 x 10(-4) M EGTA and 1 x 10(-4) M TMB-8, the 1 x 10(-7) M AVP-mobilized [Ca++]i was completely abolished. In the presence of 5 x 10(-4) M 3-isobutyl-1-methylxanthine, AVP increased cellular cyclic AMP (cAMP) production in a dose-dependent manner. Such an AVP-induced cAMP production was significantly reduced in cells exposed to Ca(++)-free medium containing 1 x 10(-4) M EGTA. After exposure to Ca(++)-free medium containing a mixture of 1 x 10(-4) M EGTA and 1 x 10(-4) M TMB-8, the cAMP response to AVP was markedly reduced.(ABSTRACT TRUNCATED AT 250 WORDS)
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