Membrane activation of smooth muscle from rabbit basilar artery by dopamine

Intracellular membrane potential (EM) and force development were measured in rabbit basilar artery to help elucidate the mechanism of action of dopamine in this preparation. There was a strong correlation between membrane depolarization and contraction (r = 0.95) between 3 X 10-7 M to 10-4 M dopamine. When the vascular muscle cells were depolarized by elevating [K]0 there was a Em dependent decrease in force development in response to dopamine. Significant reduction of dopamine stimulated force development was observed when the vessel was depolarized by 5-6 mV by excess extracellular K+ and 90% inhibition was seen when the artery was depolarized to -20mV. When Ca++ influx was blocked, dopamine no longer induced force development. Such findings suggest that dopamine contracts rabbit basilar artery by a mechanism involving membrane depolarization. This process may involve an influx of extracellular Ca++ through voltage sensitive channels.