Intracellular angiotensin II elicits Ca2+ increases in A7r5 vascular smooth muscle cells

Recent studies show that angiotensin II can act within the cell, possibly v ia intracellular receptors pharmacologically different from typical plasma membrane angiotensin II receptors. The signal transduction of intracellular angiotensin LI is unclear. Therefore. we investigated the effects of intra cellular angiotensin Il in cells devoid of physiological responses to extra cellular angiotensin II (A7r5 vascular smooth muscle cells). Intracellular delivery of angiotensin II was obtained by using liposomes or cell permeabi lisation. Intracellular angiotensin II stimulated Ca2+ influx, as measured by Ca-45(2+) uptake and single-cell fluorimetry. This effect was insensitiv e to extracellular or intracellular addition of losartan (angiotensin AT, r eceptor antagonist) or PD123319 ((s)-1-(4-[dimethylamino]-3-methylphenyl)me thyl-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carb oxylate) (angiotensin AT, receptor antagonist). Intracellular angiotensin I I stimulated inositol-1,4,5-trisphosphate (Ins(1,4,5,)P3) production and in creased the size of the Ins(1,4,5,)P, releasable Ca-45(2+) pool in permeabi lised cells, independent of losartan and PD123319. Small G-proteins did not participate in this process, as assessed by using GDP betaS. Intracellular delivery of angiotensin I was unable to elicit any of the effects elicited by intracellular angiotensin II. We conclude from our intracellular angiot ensin application experiments that angiotensin II modulates Ca2+ homeostasi s even in the absence of extracellular actions. Pharmacological properties suggest the involvement of putative angiotensin non-AT(1)-/non-AT(2) recept ors. (C) 2001 Elsevier Science B.V, All rights reserved.