Key result
Vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 alter rat heart myosin isozyme expression via complex regulation.
Why the study?
The regulation of myosin isozyme expression by vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 in the heart and its relation to contractility is not fully understood.
Vitamin D3 status influences myosin isozyme expression in the rat heart through a complex system of direct and indirect effects.
Rat data on vitamin D and cardiac myosin should not change practice; leaves open human translation and therapeutic relevance.
In this report, we demonstrate a significant inverse correlation between contractility and serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] levels and no correlation between contractility and serum levels of calcium, phosphate, or PTH. We also examined myosin isozyme distribution in vitamin D3-deficient rats, because myosin isozyme distribution can alter contractility. There was a significant increase in the levels of the V1 myosin isozyme in animals raised on a vitamin D3-deficient diet that maintained normal serum calcium and phosphate levels. There was no difference in the relative myosin isozyme distribution in animals raised on a hypocalcemia-yielding vitamin D3-deficient diet vs. animals raised on a control diet. As increased contractility has been observed in both groups of vitamin D3-deficient animals, a shift in myosin isozyme distribution cannot solely explain the increase in contractility previously observed in the vitamin D3-deficient rat heart. To determine whether 1,25-(OH)2D3 directly regulates myosin isozyme levels, we analyzed myosin isozyme distribution in primary cultures of ventricular myocytes. We found that 1,25-(OH)2D3 reduces total myosin levels, but does not alter myosin isozyme distribution. Thus, we show that the influence of vitamin D3 status on myosin isozyme expression in the intact rat involves a complex regulatory system of direct and indirect effects.
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O’Connell et al. (1994) studied Vitamin D3 deficiency. Vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 vs. Control diet was evaluated on Myosin isozyme distribution and contractility. Vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 influence myosin isozyme expression in the rat heart through a complex regulatory system of direct and indirect effects.