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 capacitative calcium influx to intracellular calcium levels during agonist-induced stimulation of vascular smooth muscle cells.


METHODS
Aortic vascular smooth muscle cells (A7r5) were loaded with Indo-1 and intracellular calcium transients were measured. Cells were challenged with either arginine vasopressin (0. 5 microM) or thapsigargin (1 microM). 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 regression provided a time constant that describes restoration of ionic equilibrium involving both sequestration and extrusion pathways.


RESULTS
Stimulation of cells with thapsigargin produced a non-L-type calcium influx that was attenuated by lanthanum. Cells excited with vasopressin exhibited a rapid calcium increase followed by a gradual decrease to a plateau level. Lanthanum pretreatment prior to stimulation caused no significant change in baseline, peak or plateau calcium levels as compared to control. Lanthanum caused 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 contribute significantly to the vasopressin response.
Gardner
J D
JD
Department of Physiology, University of South Alabama, Mobile, AL 36688USA.
Benoit
J N
JN
D000818:Animals; D001011:Aorta / Q000196:embryology; D001127:Arginine Vasopressin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D004553:Electric Conductivity; D007211:Indoles; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008856:Microscopy, Fluorescence; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D019284:Thapsigargin / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D020746:Calcium Channels, L-Type; D007211:Indoles; D001127:Arginine Vasopressin; D019284:Thapsigargin; D007811:Lanthanum; C048960:indo-1; D002118:Calcium