Regulation of sodium current development in cultured atrial tumor myocytes (AT-1 cells)

AT-1 cells, derived from atrial tumors in transgenic mice, have many features similar to cardiac myocytes. However, their sodium current (INa) has not been evaluated on detail. In this study, two INa phenotypes were identified in AT-1 cells: one at 3 days in culture and the other at 14 days. INa was smaller at 3 days than at 14 days (12 +/- 2 vs. 37 +/- 5 pA/pF) and activated more slowly (time to peak INa at -30 mV: 9.8 +/- 0.4 vs. 1.4 +/- 0.1 ms). Inactivation at 14 days was faster and shifted 16 mV negative compared with that at 3 days. Acute protein kinase A or C stimulation in 3-day cells did not alter INa gating. However, the 14-day phenotype was observed in 3-day cells when the adenosine 3',5'-cyclic monophosphate analogue 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, the phorbol ester phorbol 12-myristate 13-acetate, or okadaic acid was added to the culture medium from days 0 to 3. Conversely, adenosine 3',5'-cyclic monophosphothioate triethylamine, the protein kinase A inhibitor, prevented the normal development of the 14-day phenotype if the exposure was early and reverted the phenotype to that at 3 days if the exposure was later. Thus, in AT-1 cells, as in other mammalian cardiac myocytes, INa undergoes a maturation process that is dependent on intracellular phosphorylation processes. The data raise the possibility that an important consequence of altered intracellular signaling in disease is lability in INa amplitude or gating.