AJP - Cell Physiology, Vol 263, Issue 4 C750-C758, Copyright © 1992 by American Physiological Society
Effects of angiotensin II and nonpeptide receptor antagonists on transduction pathways in rat proximal tubule
J. Poggioli, G. Lazar, P. Houillier, J. P. Gardin, J. M. Achard and M. Paillard
Laboratoire de Physiologie et Endocrinologie Cellulaire Renale, Universite Pierre et Marie Curie, Hopital Broussais, Paris, France.
Because the presence of the angiotensin II (ANG II)-dependent
phosphoinositide hydrolysis has been questioned from studies in proximal
cells in culture, we looked for this transduction pathway in suspension of
freshly isolated rat proximal tubule fragments. ANG II-receptor activation
induced a prompt (within 15 s) and sustained increase in [3H]inositol
phosphates (IPs; inositol trisphosphate, inositol bisphosphate, and
inositol monophosphate). In fura-2-loaded tubules, it elicited a rapid and
biphasic rise in cytosolic free calcium ([Ca2+]i) with an early peak
(within 15 s) followed by a plateau. The peak was maintained in the absence
of extracellular calcium. ANG II-induced inositol trisphosphate and [Ca2+]i
rises showed a similar dose dependency, with a 50% effective concentration
(EC50) of 2.9 and 5.5 nM, respectively. We checked that ANG II inhibited
basal (EC50 4.4 nM) and parathyroid hormone- and forskolin-stimulated cAMP
production, the latter effect being inhibited by pertussis toxin
pretreatment. The effects of ANG II on IPs and [Ca2+]i were inhibited by
the ANG II receptor subtype 1 (AT1) antagonist losartan and not by the ANG
II receptor subtype 2 (AT2) antagonists PD 123177 and PD 123319. The effect
of ANG II on forskolin-stimulated cAMP was inhibited by losartan and not by
PD 123319. In agreement with these results, specific binding of
125I-[Sar1,Ile8]ANG II was markedly inhibited by losartan, whereas PD
123319 had no effect. These results demonstrate that AT1 receptor subtypes
are present in intact rat proximal tubule cells and are coupled to both
IPs-Ca2+ and cAMP signaling pathways. No evidence for AT2 receptor subtype
is found.
