Effects of activin A on ionic channels in human FSH‐secreting tumour cells.

1. Effects of activin A on ionic channels were examined in human FSH‐secreting tumour cells using electrophysiological techniques. 2. Under voltage clamp with the conventional whole‐cell clamp technique, the voltage‐gated Na+ channel, the T‐ and L‐type Ca2+ channels, the delayed K+ channel and the A‐channel were observed. 3. With the nystatin‐perforated whole‐cell clamp technique, the same voltage‐gated channels were recorded. Activin A (10(‐7) M) increased the amplitude of the L‐type Ca2+ current, whereas it decreased the amplitude of the delayed K+ current. 4. Under current clamp with the perforated whole‐cell clamp technique, more than 80% of the cells exhibited spontaneous action potentials. Application of 10(‐7) M activin A depolarized the membrane with a conductance increase and augmented action potential frequency. The reversal potential of the activin A‐induced current was ‐20 to 0 mV. The activin A‐induced current was abolished in a Na(+)‐free extracellular solution, indicating that the membrane depolarization caused by activin A was due to the conductance increase to Na+ ions through non‐selective cation channels.