Beta3-Adrenergic Receptor & Progression to Heart Failure

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DESCRIPTION (provided by applicant): Preliminary data from our laboratory revealed that in CHF, beta3-adrenergic receptor (AR) stimulation-induced cardiac depression on the normal myocardium is amplified, thus suggesting a direct adverse functional consequence of beta3-ARs activation in CHF. The purpose of this grant is to 1) characterize alterations of a3-AR-mediated functional responses of left ventricle (LV) before and as CHF progresses and assess the time course to establish a contributing causal role of cardiac beta3-AR in the abnormal responsiveness of catecholamine (NE) with CHF; and 2) define the cellular and molecular mechanisms of the altered beta3-AR-mediated inotropic response. We will test Hypothesis: [H1] after CHF, cardiac functional responses to exogenous and endogenous NE are altered due to (i) attenuated beta1-AR-mediated positive inotropic responses and (ii) an enhanced beta3-AR-mediated depression in LV and myocyte contraction and relaxation. (iii) During exercise with CHF, the adverse functional effects of beta3 -AR activation in CHF may be accentuated, due to increases in circulating and myocardial levels of NE, which [H2] (i) results from an increased expression of beta3-AR in CHF myocytes, (ii) accompanied with an enhanced negative modulation on [Ca2+]i regulation. (iii) These effects are linked with Gi, (iv) involving both nitric oxide (NO)-dependent and NO-independent signal transduction pathways. [H3] Chronic a1-AR blocker may attenuate, while beta3-AR antagonist may prevent LV and myocyte functional impairment and limits the progression of CHF. Studies will be conducted in chronically instrumented conscious dogs before and after pacing-induced CHF at rest and during exercise and in myocytes isolated from LV myocardium obtained by biopsy from these same animals before and after CHF. We will compare myocyte beta3-AR mRNA and protein levels; and LV and myocyte contractile, [Ca 2+]i transient, and Ca 2+ current responses to beta3- AR agonist or beta3-AR antagonist before and as CHF progresses and CHF after received three weeks of treatment with beta1-and beta3-AR blockers. The involvement of NO, and inhibitory G proteins in receptor-activated signal transduction will be evaluated by using L-NAME, and PTX. These studies will be the first detailed longitudinal study of the cardiac beta3-AR gene expression, and its functional effects at rest and during exercise before and during the progression of CHF in a clinically relevant higher mammal model of CHF. These studies are necessary to extend our knowledge regarding the cardiac beta-AR regulation and the role of these receptors in the abnormal responsiveness of catecholamine in CHF. Thus, provide valuable new insight into the mechanism of the progression of functional impairment in CHF, and may assist in specifically targeting therapy for CHF.