NITRIC OXIDE SUPPRESSION OF DIABETIC HEART CONTRACTION

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The overall hypothesis of this proposal is that inducible nitric oxide synthase (iNOS) is elevated in cardiac myocytes during the development of insulin-deficient diabetes mellitus and the subsequent production of nitric oxide (NO) and cGMP suppress the response of the cardiac myocyte to beta-adrenergic stimulation. The specific aims to address this hypothesis are as follows: (A) To determine if NO production in the diabetic cardiac myocyte modulates the beta-adrenergic stimulation of contraction. It is hypothesized that the production of NO by iNOS decreases the beta-adrenergic stimulation of contraction in diabetic cardiac myocytes. Moreover, it is hypothesized that inhibition of iNOS will enhance beta-adrenergic stimulation of contraction in diabetic cardiac myocytes. (B) To determine if NO production in the diabetic cardiac myocyte modulates the beta-adrenergic stimulation of calcium current. It is hypothesized that production of NO by iNOS decreases the beta-adrenergic stimulation of calcium current (ICa) in the diabetic cardiac myocyte and that inhibition of iNOS will enhance B-adrenergic stimulation of ICa. (C) To determine if cGMP production mediates the suppression of beta-adrenergic-stimulated calcium current and contraction in the diabetic cardiac myocyte. It is hypothesized that increased production of cGMP in the diabetic cardiac myocyte suppresses Beta- adrenergic stimulation of ICa and contraction. It is further hypothesized that an increased production of NO by iNOS results in an increased production of cGMP in the cardiac myocyte. Therefore, inhibition of cGMP production will enhance the beta-adrenergic stimulation of both ICa and contraction in diabetic cardiac myocyte. Diabetes will be induced by intravenous streptozotocin injection (60 mg/Kg). Isolated cardiac myocytes will be used to measure nitric oxide, cGMP and cAMP production. These parameters will be correlated with measurements of cardiac myocyte contraction and calcium currents using whole cell voltage clamp techniques. Measurements will be determined under basal conditions, in response to isoproterenol, and in the presence of selective nitric oxide synthase inhibitors.