Partial characterization of the rH1 sodium channel protein from rat heart using subtype-specific antibodies

Three subtype-specific antisera were generated against peptides corresponding to portions of the amino terminus, interdomain 1-2, and carboxy terminus of the rH1 sodium channel primary sequence to confirm the expression of this protein in the adult rat heart and to determine selected biochemical properties of this protein that might contribute to its subtype-specific characteristics. All three antisera identify a 240-kD band on Western blots of partially purified cardiac membrane proteins and by immunoprecipitation of iodinated partially purified membrane proteins. Unlike other characterized mammalian sodium channels, no beta subunit is detected in association with the rH1 alpha subunit. The rH1 alpha subunit is a complex sialoglycoprotein as evidenced by its interaction with wheat germ agglutinin-Sepharose and by reduction in its apparent molecular weight after treatment with neuraminidase; deglycosylation with N-glycanase confirms that the rH1 protein contains significantly less carbohydrate than other sodium channel proteins characterized to date (5% versus 25% to 30%). Consistent with electrophysiological studies indicating a role of phosphorylation in channel regulation, the rH1 alpha subunit can be phosphorylated by the catalytic subunit of cAMP-dependent protein kinase A. The possible functional significance of these findings is discussed.