Vasopressin responses in electrically coupled A7r5 cells

Changes in cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and in membrane potential were monitored in single A7r5 smooth-muscle cells during spontaneous spiking and after arginine vasopressin stimulation. Spontaneous Ca²⁺ oscillations, which were associated with the occurrence of action potentials, occurred in about 90% of the confluent monolayers investigated. This spontaneous activity was synchronized amongst all the cells of the monolayer, indicating that the cells were electrically coupled. Arginine vasopressin stimulation produced a [Ca²⁺]_i rise that was about 5 times higher than the amplitude of the spontaneous Ca²⁺ oscillations and resulted in a subsequent cessation of spontaneous electrical 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 [Ca²⁺]_i rises. We conclude that agonist-induced [Ca²⁺]_i increases in an electrically coupled cell monolayer can be asynchronous.