The goal of the proposed studies is to determine the mechanism of desensitization of the perivascular nerve (PvN) calcium-sensing receptor (CaR)-mediated intracellular calcium (Ca2+i) mobilization in nerve endings of resistance arteries. Hypertension is prevalent in the US and common in the African American community, where it is linked with diabetes and end organ damage. We hypothesized that local increases in interstitial Ca2+ induce vasorelaxation by activating the PvN CaR and subsequent release of a vasodilator. We propose to test the hypothesis that PvN CaR-mediated mobilization of Ca2+i within sensory nerves, coupled to G?q, is desensitized by G protein receptor kinase 2 (GRK2)-mediated uncoupling of the receptor from G protein. We will employ pharmacological agents, immunoprecipitation, Western blotting, Ca2+i measurement by Fura-2 microfluorimetry, siRNA knockdown of specific genes, C-terminal truncation and site-directed mutagenesis in these studies.
Specific aim 1 will determine the roles of specific G proteins in the mechanism of agonist-dependent desensitization of PvN CaR-mediated Ca2+i mobilization.
Specific aim 2 will determine the role of GRK2-mediated receptor phosphorylation in the desensitization of PvN CaR-mediated Ca2+i mobilization.
Specific aim 3 will truncate the C-terminal domain and mutate specific amino acids in this domain to determine their roles in regulating G protein coupling and identify the source of the differences in Ca2+ signaling between PvN and human parathyroid (HuPT) CaRs. We anticipate that these studies will provide a more complete understanding of the mechanisms of activation and desensitization of the PvN CaR in nerve terminals on resistance arteries and provide information on the mode of regulation of the receptor and its Ca2+ signaling properties. Information from these studies will form the basis for future studies to establish the signaling pathway between PvN CaR activation and release of vasodilator compounds. The studies may reveal, i) the PvN nerve CaR as a potential anti-hypertensive target and, ii) new targets for the development of novel vasodilator compounds. This award will enable me to rapidly expand my research program at NCCU and increase my research productivity to enabe me to compete for non-SCORE sources of funding. In addition, the proposed studies will provide training opportunities for under-represented minority students at NCCU and prepare them for future careers in biomedical research.
Clinical trials indicate that high calcium intake and diets high in fruits, vegetables, and low-fat milk lower blood pressure in hypertension (Appel et al., 1997;MaCarron et al., 1999;Nowson et al., 2004;2005;van Mierlo et al., 2006;Bergel et al., 2007;van Mierlo et al., 2008), but there is no plausible mechanism to explain this phenomenon. The sensory nerve network on blood vessels (Bukoski et al., 1997;Bukoski, 1998;2001; Awumey et al., 2008) expresses a calcium receptor that may play a role in dietary calcium-mediated reduction in blood pressure. The proposed studies may lead to identification of specific targets for the development of new anti-hypertensive drugs.
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