Regulation of caveolar cardiac sodium current by a single Gs histidine residue

Palygin OA, Pettus JM, Shibata EF. Regulation of caveolar cardiac sodium current by a single Gs histidine residue. Am J Physiol Heart Circ Physiol 294: H1693–H1699, 2008. First published February 8, 2008; doi:10.1152/ajpheart.01337.2007.—Cardiac sodium channels (voltage-gated Na channel subunit 1.5) reside in both the plasmalemma and membrane invaginations called caveolae. Opening of the caveolar neck permits resident channels to become functional. In cardiac myocytes, caveolar opening can be stimulated by applying -receptor agonists, which initiates an interaction between the stimulatory G protein subunit(Gs ) and caveolin-3. This study shows that, in adult rat ventricular myocytes, a functional Gs -caveolin-3 interaction occurs, even in the absence of the caveolin-binding sequence motif of Gs . Consistent with previous data, whole cell experiments conducted in the presence of intracellular PKA inhibitor stimulation with -receptor agonists increased the sodium current (INa) by 35.9 8.6% (P 0.05), and this increase was mimicked by application of Gs protein. Inclusion of anti-caveolin-3 antibody abolished this effect. These findings suggest that Gs and caveolin-3 are components of a PKA-independent pathway that leads to the enhancement of INa. In this study, alanine scanning mutagenesis of Gs (40THR42), in conjunction with voltage-clamp studies, demonstrated that the histidine residue at position 41 of Gs (H41) is a critical residue for the functional increase of INa. Protein interaction assays suggest that Gs FL (full length) binds to caveolin-3, but the enhancement of INa is observed only in the presence of Gs H41. We conclude that Gs H41 is a critical residue in the regulation of the increase in INa in ventricular myocytes.