The Effects of Ca Antagonists, Manganese and Lanthanum on Cooling-Induced Contracture of Depolarized Vas Deferens

Abstract

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.