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.
Takano
K
K
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Ogata
E
E
Yamashita
N
N
D028341:Activins; D000236:Adenoma / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D006801:Humans; D007265:Inhibins / Q000494:pharmacology*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials; D015221:Potassium Channels / Q000187:drug effects; D015222:Sodium Channels / Q000187:drug effects; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D007473:Ion Channels; D015221:Potassium Channels; D015222:Sodium Channels; D028341:Activins; D007265:Inhibins; D005640:Follicle Stimulating Hormone