Membrane activation of smooth muscle from rabbit basilar artery by dopamine

Intracellular membrane potential (E_m) 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 3×10^–7 M to 10^–4 M dopamine. When the vascular muscle cells were depolarized by elevating [K]_o there was a E_m 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 cotracts rabbit basilar artery by a mechanism involving membrane depolarization. This process may involve an influx of extracellular Ca⁺⁺ through voltage sensitive channels.