There are at least nine adrenergic receptor (AR) subtypes which mediate responses to norepinephrine and epinephrine, which are grouped into three families with similarities in structure, pharmacology, and signalling. These subtypes coexist on cells, and responses to catecholamines are often due to activation of multiple subtypes. The principal investigator's research efforts involve continuing to examine these interactions and their functional implications in brain. During the next project period, the hypothesis that closely related betaAR subtypes differ in their efficiencies of coupling to Gs/adenylate cyclase will be tested. In addition, experiments are designed to evaluate whether coexistence of these subtypes results in converging signals which can be additive, redundant or synergistic dependent on subtype density and ratio. Experiments will be performed in cell lines that normally express no AR subtypes. Inducible and repressible vectors will be used to control the densities and ratios of rat beta1 and beta2ARs, and efficiency of coupling will be quantified by relating receptor density to the ability of agonists to stimulate responses, ranging from GTPgS binding to stimulation of cAMP in whole cells. Selective agonists and antagonists will be used to compare coupling efficiencies of subtypes activated alone or in combinations. There are three specific aims: 1. Compare the coupling efficiencies of rat beta1 and beta2ARs in two different cell lines. 2. Examine the importance of the expression level of Gsa and its isoforms in the coupling efficiency of each subtype. 3. Determine the interactions between converging signals initiated by beta1 and 2ARs when coexpressed in various densities and ratios. These studies will provide specific information on signalling by catecholamine neurotransmitters, and insights into the implications of coexisting subtypes in cells. Since betaAR subtypes are known to coexist on cells and mediate converging responses, this will be useful in understanding the mechanisms and potential therapeutic approaches for a variety of diseases from depression to hypertension.
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