Intracellular actions of angiotensin II in vascular smooth muscle cells

Angiotensin II (AngII) is present inside vascular smooth muscle cells (VSMC ); however, its intracellular functions, if any, are unknown. AngII was adm inistered by microinjection. AngII was identified in endosomes and in the n ucleus. Microinjection of AngII (10(-10) M) led to a rapid increase in the intracellular Ca2+ concentration ([Ca2+](i)) in the cytosol and in the nucl eus. The [Ca2+](i) increase was the result of an influx of extracellular Ca 2+ ions. The intracellular AngII effect was totally inhibited by concomitan t injection of the AngII type 1 receptor blocker candesartan. Desensitizati on of extracellular AngII receptors, on the other hand, did not influence t he intracellular effects, and neither did extracellular candesartan. The in crease in [Ca2+](i) was observed not only in the microinjected cell but als o in directly adjacent VSMC. In contrast to the microinjected cells, the [C a2+](i) increase in the adjacent cells was mostly the result of Ca2+ releas e from intracellular stores. Pretreatment with thapsigargin, which interfer es with Ca2+ release from intracellular stores, abolished the AngII respons e in adjacent cells. Microinjection of inositol trisphosphate induced a [Ca 2+](i) response in adjacent cells that was similar to the AngII-induced eff ects. Preincubation of VSMC with uncoupling substances did not decrease the AngII response but prevented a [Ca2+](i) surge in adjacent cells. Tyrosine phosphorylation was next examined. Phosphorylation was detected in the inj ected cells, primarily in the cytoskeleton. It can be concluded that intrac ellular AngII binds to intracellular AngII receptors and elicits increased [Ca2+](i) in the injected cell and then in cells in the immediate neighborh ood. Cell-cell contact is necessary for the AngII-mediated effects. These d ata suggest that intracellular AngII may stimulate a cluster of VSMC from a single cell, via the release of second messengers.