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Lowering of temperature applied during the course of the tonic contraction of high-K-induced contracture of guinea-pig vas deferens induced an increase in tension which was sensitive to extracellular Ca. Verapamil and nifedipine inhibited the tonic contraction and cooling-induced tension development. Mn2+ and La3+ also showed inhibiting actions on the tonic contraction, which, however, was followed by slow re-elevation of the tension. Cooling treatment caused relaxation in the presence of either ion, which increased with repetition of the cooling treatment. By rewarming the preparation, a phasic contraction, which increased in height with repetition of the treatment, was observed. These effects in the presence of Mn2+ or La3+ were also observed in the absence of Ca or in preparations treated with caffeine in Ca-free solution (Ca-deprived preparation). Verapamil was capable of depressing these effects of Mn2+ and La3+. These results suggest the involvement of influxed Ca in the initiation of tension development by cooling. The decrease of extrusion through the cell membrane and/or uptake by intracellular binding sites at low temperature may be the cause of the cooling-induced tension development. Mn2+ or La3+ induces the tension development by their direct actions on contractile proteins which are differently affected by the changes in temperature.

The effects of Ca antagonists, manganese and lanthanum on cooling-induced contracture of depolarized vas deferens.