Veratridine actions on two types of fast Na+ channels in human uterine leiomyosarcoma cells.
In human uterine leiomyosarcoma cell line (SK-UT-1B), we previously demonstrated two types of fast Na+ current (INa(f)) induced by serum, based on different time course of current decay: fast-inactivating and slow-inactivating. To further clarify the properties of these currents, we studied the effects of veratridine, which is known to modify the inactivation process of INa(f), using whole-cell voltage clamp. Bath application of veratridine (100 microM) produced a decrease in peak INa(f) (Ipeak), simultaneous with increase in the steady-state current (Iss) and tail current (Itail). These effects of veratridine were observed in only slow-inactivating INa(f). The induction of Iss and Itail was completely reversed by washout of veratridine within 5 min, whereas the decreased Ipeak did not recover even after 15 min of washout. These findings suggest that the fast Na+ channels in this cell line may have two binding sites for veratridine: a high-affinity site, involved in the decrease in Ipeak (possibly due to a decrease in conductance), and a low-affinity site, related to the appearance of Iss and Itail (due to a long opening of the channels). It is concluded that the two types of INa(f) in this cell line have different sensitivity to veratridine and the fast Na+ channels may have two binding sites for veratridine.
Kusaka
M
M
Department of Molecular and Cellular Physiology, University of Cincinnati, OH 45267-0576.
Sperelakis
N
N
D005260:Female; D006801:Humans; D007890:Leiomyosarcoma / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology*
D015222:Sodium Channels; D014701:Veratridine