Effects of capacitative calcium entry on agonist-induced calcium transients in A7r5 vascular smooth muscle cells

Objective: The purpose of this study was to evaluate the contribution of ca pacitative calcium influx to intracellular calcium levels during agonist-in duced stimulation of vascular smooth muscle cells. Methods: Aortic vascular smooth muscle cells (A7r5) were loaded with Indo-1 and intracellular calci um transients were measured. Cells were challenged with either arginine vas opressin (0.5 mu M) or thapsigargin (1 mu M). Lanthanum (1 mM) was used to block capacitative calcium influx through store-operated channels. Calcium traces were analyzed for basal, peak and plateau responses. Recordings were derivatized and integrated to gain additional information. Nonlinear regre ssion provided a time constant that describes restoration of ionic equilibr ium involving both sequestration and extrusion pathways. Results: Stimulati on of cells with thapsigargin produced a non-L-type calcium influx that was attenuated by lanthanum, Cells excited with vase pressin exhibited a rapid calcium increase followed by a gradual decrease to a plateau level. Lantha num pretreatment prior to stimulation caused no significant change in basel ine, peak or plateau calcium levels as compared to control. Lanthanum cause d no significant change in maximal calcium release rate, calcium integrals or time constant as compared to control, Conclusions: Capacitative calcium entry can occur in vascular smooth muscle cells, but does not appear to con tribute significantly to the vasopressin response. Copyright (C) 2000 Natio nal Science Council, ROC and S. Karger AG, Basel.