Temperature-dependence of 45Ca fluxes and contraction in vascular smooth muscle cells of rabbit ear artery.

The effect of cooling from 35 to 20 degrees C on the 45Ca-exchange and on the contractile response of rabbit ear artery has been investigated. The amplitude of the contraction induced by K-depolarization at 20 degrees C is reduced to about 60% of its value at 35 degrees C, whereas the response to noradrenaline is not significantly affected. Cooling induces a 2 to 4-fold reduction of the 45Ca-efflux rate. This effect also occurs in Ca-free medium and in solutions containing 1 mM La. It also occurs in Na-free medium and in tissues in which the transmembrane Na-gradient has been reduced. At 20 degrees C, the 45Ca-influx in unstimulated tissues and in K-depolarized preparations is significantly lower than at 35 degrees C. In Ca-depleted tissues, i.e. tissues in which the noradrenaline-sensitive Ca-store has been emptied by a stimulation with the agonist in Ca-free solution, the 45Ca-influx is not significantly affected by cooling. The gradual depletion of the noradrenaline-sensitive Ca-store in Ca-free solutions is at 20 degrees C much slower than at 35 degrees C. The amount of Ca released by noradrenaline is not affected by cooling, whereas for the same amount of Ca released the contractile response is higher at 20 degrees C. These findings indicate that temperature affects the transmembrane Ca-extrusion and the Ca-influx through voltage-dependent channels. The properties of the noradrenaline-sensitive Ca-store are less sensitive to temperature.