Stretch of vascular smooth muscle activates tone and 45Ca2+ influx

A number of blood vessels develop and maintain an active tone when stretched in vitro. The magnitude of this tone is related to the concentration of extracellular Ca2+. We propose that stretch-induced tone is primarily associated with 45Ca2+ influx, and is minimally affected by the release of intracellular stores of Ca2+. The characteristics of stretch-induced 45Ca2+ influx and tone are distinct from those due to depolarization with K+ and are not dependent on the endothelium. Stretch-induced tone was not altered by increases in the extracellular concentration of K+ nor by removal of the endothelium. Activators of protein kinase C increased, while inhibitors of the enzyme attenuated, stretch-induced tone. We propose that in some blood vessels, stretch per se allows the Ca2+ influx that leads to tone. Stretch-induced tone may be regulated by protein kinase C.