Glycosylation influences voltage-dependent gating of cardiac and skeletal muscle sodium channels

The role of glycosylation on voltage-dependent channel gating for the clone d human cardiac sodium channel (hH1a) and the adult rat skeletal muscle iso form (mu l) was investigated in HEK293 cells transiently transfected with e ither hH1a or mu 1 cDNA. The contribution of sugar residues to channel gati ng was examined in transfected cells pretreated with various glycosidase an d enzyme inhibitors to deglycosylate channel proteins. Pretreating transfec ted cells with enzyme inhibitors castanospermine and swainsonine, or exo-gl ycosidase neuroaminidase caused 7 to 9 mV depolarizing shifts of V-1/2 for steady-state activation of hH1a, while deglycosylation with corresponding d rugs elicited about the same amount of depolarizing shifts (8 to 9 mV) of V -1/2 for steady-state activation of mu 1. Elevated concentrations of extrac ellular Mg2+ significantly masked the castanospermine-elicited depolarizing shifts of V-1/2 for steady-state activation in both transfected hH1a and m u 1. For steady-state activation, deglycosylation induced depolarizing shif ts of V-1/2 for hH1a (10.6 to 12 mV), but hyperpolarizing shifts for mu 1 ( 3.6 to 4.4 mV). Pretreatment with neuraminidase had no significant effects on single-channel conductance, the mean open time, and the open probability . These data suggest that glycosylation differentially regulates Na channel function in heart and skeletal muscle myocytes.