Na-PUMP GENE EXPRESSION IN HYPERTROPHIC HEARTS

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Na, K-ATPase (Na, K-pump) maintains intracellular ion composition by transporting Na^+ and K^+across the cell membrance, and plays an important role in many fundamental cellular and physiological processes such as the control of contractility, excitability, and cell volume regulation. The Na, K-ATPase protein comprises two subunits, a large catalytic alpha subunit and a smaller glycosylated beta subunit. At least three alpha subunit isoforms, alpha1, alpha2 and alpha3, and two beta subunit isoforms, beta1 and beta2, have been characterized in rats and humans. With the support of the Grant-in-Aid fro Scientific Research (A), we have revealed that ; (1) The expression of Na, K-ATPase alpha and beta subunits in cardiocytes in vitro was directly regulated at a transcriptional level by thyroid and aldosterone hormones, or Na^+, (2) In the hypertrophic hearts of spontaneously hypertensive rats (SHR), Na, K-ATPase mRNA expression was augmented compared with normotensive rats (WKY) at the pre-hypertensive stage of 4-week-old, (3) In the in vivo failing hearts of Syrian hamsters (Bio14.6), the expression of cardiac Na, K-ATPase gene was down-regulated compared with normal hamsters (Flb). Thus the alterations of Na, K-ATPase gene expression might play an important roll in the pathogenesis of cardiac hypertrophy and cardiomyopathy.