Congestive heart failure is a major health problem in an aging population. Secondary hyperaldosteronism significantly complicates the management of this disorder. Excessive aldosterone production increases intravascular volume and enhances myocardial fibrosis, and thus accelerates the decline of the failing heart. Novel strategies to suppress hyperaldosteronism would be of special therapeutic value to congestive heart failure patients with renal insufficiency. The overall hypothesis of this research project is that low threshold, T-type, Ca+ channel activity underlies the physiological regulation of aldosterone secretion and sets the response of the adrenal glomerulosa cell to activation by its major physiological regulator, angiotensin II. T-type Ca+ channel activity is modulated by the activity of Ca+/calmodulin (CaM) dependent protein kinase ll. Activation of this kinase lowers the voltage-response of the T-type Ca+ channel, enabling more channels to open at a lower voltage, and thus, more Ca+ to be delivered into the cell interior for cell activation. The focus of the proposed work is two-fold: to define the mechanism by which Ca+/CaM-dependent protein kinase regulates T-type Ca+ channels in isolated bovine adrenal glomerulosa cells; and to determine the extent to which this mechanism is invoked by and/or modified by glomerulosa cell secretagogues (extracellular K and angiotensin II (Ang II)) in their control of aldosterone secretion. They will use a combination of techniques including: the patch-electrode voltage-clamp to assess channel activity; single cell fluorescence to measure intracellular Ca+ homeostasis; immunological methods of immunoprecipitation and Western blotting to assess the activation state of Ca+/CaM-dependent protein kinase II (CKII) and the beta subunit of the Ca+ channel during cell stimulation.
The Specific Aims are: 1) to determine the mechanism by which CKII regulates T-channel activity; 2) to determine the mechanism(s) of Ang II-receptor activation that result in changes in T-channel activity; and 3) to determine the role of CKII regulation of T-channel activity in the physiological regulation of aldosterone secretion. The proposed studies will delineate physiological mechanisms that operate to regulate T-type Ca+ channel activity. These studies relate to the long-term clinical goal of improving the clinical management of congestive heart failure.
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