The effects of S-petasin, a sesquiterpene isolated from Petasites formosanus Kitamura, on ion currents in a mouse neuroblastoma and a rat glioma hybrid cell line, NG108-15, were examined with the aid of the whole-cell voltage-clamp technique. S-Petasin (1-300 μM) caused a decrease in the amplitude of L-type Ca2+ current (ICa,L) in a concentration-dependent manner, however, it did not change the overall shape of the current-voltage relationship of ICa,L. The IC50 value for S-petasin-induced inhibition of ICa,L was 11 μM. S-Petasin (10 μM) shifted the steady-state inactivation of ICa,L to a more negative membrane potential by approximately -10 mV. S-petasin could prolong the recovery of ICa,L inactivation. The inhibitory effect of S-petasin on ICa,L was found to exhibit tonic and use-dependent characteristics. S-Petasin could inhibit ICa,L evoked by action potential waveforms effectively. S-Petasin also suppressed low voltage-activated ICa,L in NG108-15 cells. S-Petasin at a concentration of 100 μM had little effect on voltage-dependent Na+ current; however, it did produce an inhibitory effect on delayed rectifier K+ current in a time-dependent manner. These results demonstrate that S-petasin can interact directly with L-type Ca2+ channels in NG108-15 cells. These effects could contribute to the regulation of neuronal activity if similar results were found in neurons in vivo.
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