| Abstract: | Rationale: The L-type calcium channels (LTCC) are critical for maintaining Ca ( 2+) -homeostasis. In heterologous expression studies, the RGK-class of Ras-related G-proteins regulates LTCC function; however, the physiological relevance of RGK-LTCC interactions is untested. Objective: In this report we test the hypothesis that the RGK protein, Rem, modulates native Ca ( 2+) current (ICa,L) via LTCC in murine cardiomyocytes. Methods and Results: Rem knockout mice (Rem (-/-) ) were engineered, and ICa,L and Ca ( 2+) -handling properties were assessed. Rem (-/-) ventricular cardiomyocytes displayed increased ICa,L density. ICa,L activation was shifted positive on the voltage axis, and β-adrenergic stimulation normalized this shift compared with wild-type ICa,L. Current kinetics, steady-state inactivation, and facilitation was unaffected by Rem (-/-) . Cell shortening was not significantly different. Increased ICa,L density in the absence of frank phenotypic differences motivated us to explore putative compensatory mechanisms. Despite the larger ICa,L density, Rem (-/-) cardiomyocyte Ca ( 2+) twitch transient amplitude was significantly less than that compared with wild type. Computer simulations and immunoblot analysis suggests that relative dephosphorylation of Rem (-/-) LTCC can account for the paradoxical decrease of Ca ( 2+) transients. Conclusions: This is the first demonstration that loss of an RGK protein influences ICa,L in vivo in cardiac myocytes. |
