Seasonal variation of calcium accumulation by plasma membrane enriched fraction isolated from vascular smooth muscle of the rat: Possible relationship to variation in blood pressure

The authors investigated the seasonal variation of Ca²⁺ accumulation by plasma membrane enriched fractions isolated from rat mesenteric arteries and discuss the possible implications of such a seasonal change in relation to hypertension. Data on Ca²⁺ accumulation by plasma membrane enriched fraction in the presence and absence of ATP were obtained during the period of April 1977 to March 1979. There was a rhythmic change of Ca accumulation in the presence but not in the absence of ATP, with a peak occurring in May and the lowest level in August. The seasonal variation of Ca²⁺-handling has previously been reported in microsomal fractions isolated from intestinal smooth muscle and skeletal muscle of rabbit, although the cause is not known. These findings in rats may be related to a reported seasonal variation of blood pressure and cardiovascular accidents observed in humans.