Regulation of Adenosine-activated GIRK Channels by Gq-coupled Receptors in Mouse Atrial Myocytes

Adenosine (Ado) is an important mediator of the endogenous defense against ischemia-induced injury in the heart. The action of Ado is mediated by activation of G protein-gated inwardly rectifying K+ (GIRK) channels. In turn, GIRK channels are inhibited by reducing phosphatidylinositol 4,5-bisphosphate (PIP2) through Gq protein-coupled receptors (GqPCRs). We previously found that GIRK channels activated by acetylcholine, a muscarinic M2 acetylcholine receptor agonist, are inhibited by GqPCRs in a receptor-specific manner. However, it is not known whether GIRK channels activated by Ado signaling are also regulated by GqPCRs. Presently, this was investigated in mouse atrial myocytes using the patch clamp technique. GIRK channels were activated by 100 micrometer Ado. When Ado was repetitively applied at intervals of 5~6 min, the amplitude of second Ado-activated GIRK currents (I(K(Ado))) was 88.3+/-3.7% of the first I(K(Ado)) in the control. Pretreatment of atrial myocytes with phenylephrine, endothelin-1, or bradykinin prior to a second application of Ado reduced the amplitude of the second I(K(Ado)) to 25.5+/-11.6%, 30.5+/-5.6%, and 96.0+/-2.7%, respectively. The potency of I(K(Ado)) inhibition by GqPCRs was different with that observed in acetylcholine-activated GIRK currents (I(K(ACh))) (endothelin-1>phenylephrine>bradykinin). I(K(Ado)) was almost completely inhibited by 500 micrometer of the PIP2 scavenger neomycin, suggesting low PIP2 affinity of I(K(Ado)). Taken together, these results suggest that the crosstalk between GqPCRs and the Ado-induced signaling pathway is receptor-specific. The differential change in PIP2 affinity of GIRK channels activated by Ado and ACh may underlie, at least in part, their differential responses to GqPCR agonists.

Effect of lipopolysaccharide on cytosolic Ca~(2+) and Gq protein in pulmonary microvascular endothelial cells of rats and the interferring action of anisodamine / 中国病理生理杂志

AIM: To study the effect of lipopolysaccharide(LPS) on cytosolic Ca 2+ and Gq protein in pulmonary microvascular endothelial cells of rats (RPMVECS) and the interferring action of anisodamine.METHODS: RPMVECS of Wistar rats were isolated, cultured and identified. The concentration of cytosolic Ca 2+ and Gq protein were measured by Fura-2/AM and flow cytometry, respectively.RESULTS: (1) Compared with the control group, the level of cytosolic Ca 2+ increased and the level of Gq protein decreased significantly at 30 min and 90 min after stimulation of LPS;(2) Increase in cytosolic Ca 2+ and decrease in Gq protein in RPMVECS were inhibited by anisodamine. CONCLUSION: LPS induced the increase in cytosolic Ca 2+ and the decrease in Gq protein in RPMVEC, which was inhibited by anisodamine.

Change of Gq-phosphoinositide signaling pathway in left ventricular tissue in rats with chronic heart failure and reverse effect of benazepril on it / 中国病理生理杂志

AIM: To investigate the changes of Gq-phosphoinositide pathway in left ventricular tissue of rats with chronic heart failure in order to assess the role of this signal pathway in the formation of heart failure. METHODS: Male Sprague-Dawle rats were divided into three groups: control, chronic heart failure and benazepril therapy group. Chronic heart failure was induced with adriamycin. Rats in benazepril group received benazepril 10 mg?kg-1?d-1 and adriamycin at the same time. Hemodynamic measurement was carried out after 4 weeks. The expression of G? q/11 protein in left ventricle was detected by Western blotting analysis and activity of phospholipase C was measured by the method of hydrolysis of nuclear substrate. RESULTS: Compared with control group, the ?dp/dtmax in chronic heart failure group significantly decreased, and protein G? q/11 expression, basic and stimulated phospholipase C activity significantly increased (P