Lack of muscarinic regulation of Ca2+ channels in Gi2α gene knockout mouse hearts

The purpose of the present study was to examine the role of G(i2)alpha in Ca2+ channel regulation using G(i2)alpha gene knockout mouse ventricular myocytes. The whole cell voltage-clamp technique was used to study the effects of the muscarinic agonist carbachol (CCh) and the beta -adrenergic agonist isoproterenol (Iso) on cardiac L-type Ca2+ currents in both 129Sv wild-type (WT) and G(i2)alpha gene knockout (G(i2)alpha (-/-)) mice. Perfusion with CCh significantly inhibited the Ca2+ current in WT cells, and this effect was reversed by adding atropine to the CCh-containing solution. In contrast, CCh did not affect Ca2+ currents in G(i2)alpha (-/-) ventricular myocytes. Addition of CCh to Iso-containing solutions attenuated the Iso-stimulated Ca2+ current in WT cardiomyocytes but not in G(i2)alpha (-/-) cells. These findings demonstrate that, whereas the Iso-Gsa signal pathway is intact in G(i2)alpha gene knockout mouse hearts, these cells lack the inhibitory regulation of Ca2+ channels by CCh. Therefore, G(i2)alpha is necessary for the muscarinic regulation of Ca2+ channels in the mouse heart. Further studies are needed to delineate the possible interaction of G(i) and other cell signaling proteins and to clarify the level of interaction of G protein-coupled regulation of L-type Ca2+ current in the heart.