Time-dependent expression of Na and Ca channels in PC12 cells by nerve growth factor and cAMP

Changes in voltage-dependent Na+ (INa) and Ca2+ currents (ICa) were investigated in PC12 cells cultured without or with either nerve growth factor (NGF) or 8-Br-cAMP for 10 days. Current recordings were made in the whole-cell mode by using the conventional patch-clamp technique under voltage-clamp conditions. Membrane capacitance, an indicator of the total cell surface area, was increased 3- and 1.5-fold by 10-day treatment with NGF and 8-Br-cAMP, respectively. At the same time, NGF increased the current density of both INa and ICa approximately 25 and 2.5 times greater than in their respective controls. 8-Br-cAMP also increased both current densities; the effect on the INa was one-third less than that of NGF, while the effect on the ICa was similar to that of NGF. It was concluded that NGF has strong and moderate effects, respectively, on the expression of voltage-dependent Na+ and Ca2+ channels. 8-Br-cAMP mimicked the effect of NGF especially in Ca2+ channel expression.