Angiotensin iv receptors and signalling in opossum kidney cells. Dulin, Nickolai, Zuhayr T. Madhun, Chung-Ho Chang, Liliana Berti -Mattera, David Dickens, and Janice G. Douglas. Division of Hypertension, Department of Medicine, Case Western Reserve University School of Medicine
APStracts 2:0067F, 1995.
The pharmacological properties and signalling of angiotensin IV (AIV) receptors were studied in opossum kidney cell line OK7A. Saturation binding experiments with [125I]AIV demonstrated the presence of high affinity AIV binding sites in OK7A cell membranes with Kd=0.40+/-0.08 nM and Bmax=180+/-50 fmol/mg protein. In competition experiments unlabelled AIV inhibited [125I]AIV binding biphasically: 20% of binding sites had high affinity (Ki=0.44+/-0.04 nM) and 80% had low affinity (Ki=130+/-10 nM). AIII displaced [125I]AIV from binding sites with low affinity (Ki=205+/-10 nM) and AII did not compete with [125I]AIV at concentrations up to 10 _M. The binding of AIV to OK7A cell membranes was significantly enhanced in the presence of 5 mM EDTA and completely blocked by 5 mM dithiothreitol. GTP_S inhibited the binding of [125I]AIV indicating the G-protein coupling of AIV receptors in OK7A cells. In signalling studies AIV induced transient increase in intracellular calcium concentration from 49+/-3 nM to 280+/-45 nM. AIV failed to influence phosphoinositol metabolism, indicating that Ca2+ mobilization is not linked to AIV signaling. EGTA completely abolished AIV-induced increase in [Ca2+]i consistent with Ca2+ influx. The voltage sensitive calcium channel blocking agents verapamil and nifedipin attenuated the effect of AIV on [Ca2+]i] to 133+/-33 nM and 174+/-32 nM, respectively. This data suggest that AIV induces Ca2+ influx in OK7A cells, at least partially, through the voltage sensitive Ca2+ channels. 

Received 30 January 1995; accepted in final form 24 April 1995.
APS Manuscript Number F27-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  2 May 1995.