VASOPRESSIN RESPONSES IN ELECTRICALLY COUPLED A7R5 CELLS

Changes in cytosolic Ca2+ concentration ([Ca2+](i)) and in membrane po tential were monitored in single A7r5 smooth-muscle cells during spont aneous spiking and after arginine vasopressin stimulation. Spontaneous Ca2+ oscillations, which were associated with the occurrence of actio n potentials, occurred in about 90% of the confluent monolayers invest igated. This spontaneous activity was synchronized amongst all the cel ls of the monolayer, indicating that the cells were electrically coupl ed. Arginine vasopressin stimulation produced a [Ca2+](i) rise that wa s about 5 times higher than the amplitude of the spontaneous Ca2+ osci llations and resulted in a subsequent cessation of spontaneous electri cal activity and associated Ca2+ spiking, which persisted after [Ca2+] (i) returned to baseline. Individual cells in the monolayer responded to arginine vasopressin with a different latency. Agonist-induced Ca2 waves within one cell propagated much more slowly than spontaneous [C a2+](i) rises. We conclude that agonist-induced [Ca2+](i) increases in an electrically coupled cell monolayer can be asynchronous.