The calcium binding protein tropomyosin in human platelets and cardiac tissue: elevation in hypertensive cardiac hypertrophy.

Intracellular calcium transients play a major role in the control of cellular contraction and act through binding to target proteins and inducing subsequent conformational changes and activation of enzymes. Abnormalities of intracellular calcium handling are involved in the pathophysiology of essential hypertension and cardiac hypertrophy. In this study we report on the isolation, purification and calcium binding of a 33 kDa protein from human platelets and of a 38 kDa protein from cardiac tissue, both of which are identified as tropomyosin. The calcium binding properties of these human tropomyosin isoforms indicate a putative role for these proteins in the fine tuning of the cellular contraction. Elevated tropomyosin level is demonstrated in platelets from untreated essential hypertensive patients with left ventricular hypertrophy (tropomyosin/actin: 45.1 +/- 3.5, n = 12) relative to essential hypertensive patients without cardiac hypertrophy (tropomyosin/actin: 33.8 +/- 2.3). These findings suggest an association between the enhanced expression of tropomyosin in platelets and the development of cardiac hypertrophy which may relate to the cellular calcium overload of this disease.