Temperature-dependence of45Ca fluxes and contraction in vascular smooth muscle cells of rabbit ear artery

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Abstract
The effect of cooling from 35 to 20° C on the45Ca-exchange and on the contractile response of rabbit ear artery has been investigated. The amplitude of the contraction induced by K-depolarization at 20° C is reduced to about 60% of its value at 35° C, whereas the response to noradrenaline is not significantly affected. Cooling induces a 2 to 4-fold reduction of the45Ca-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° C, the45Ca-influx in unstimulated tissues and in K-depolarized preparations is significantly lower than at 35° 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, the45Ca-influx is not significantly affected by cooling. The gradual depletion of the noradrenaline-sensitive Ca-store in Ca-free solutions is at 20° C much slower than at 35° 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° 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.