抄録
[Purpose] To characterize the electrophysiological properties of the voltage-gated sodium channel in bovine ciliary muscle cells. [Materials and methods] Smooth muscle cells enzymatically dispersed from the bovine ciliary body were used for the whole cell-voltage clamp experiments. The bath solution used was HEPES-Krebs (pH 7.4, 30°C), and pipette solution contained 100 mM-Cs+ 70 nM-Ca2+ and 200 μM-GTP (pH 7.0). The following test pulse protocols were used: (1) ramp pulses of ascending and descending directions between -120 and +80 mV from a holding potential (Hp) of -50 mV at a rate of 1 V/s (200 ms duration); (2) depolarizing steps of 100 ms duration from Hp=-80 mV to a voltage between -110 and +80 mV; and (3) pre-conditioning by a long (5 s) step pulse from a Hp of -80 mV to a voltage between -110 and +80 mV followed by an abrupt switch to 0 mV. [Results] Ascending ramp-pulses evoked an inward current having a peak of -40 to -200 pA at -10 to 0 mV, which was not observed when the descending ramp-pulse protocol was used. The current was dose-dependently inhibited by superfusion of tetrodotoxin (Ki=3.1 nM, n=21). The voltage-current relationships obtained by both step and ramp pulse protocols showed a peak at -10 mV and a polarity reversal at about +14 mV. A 50% inactivation by conditioning pulses occurred at -46±2 mV (n=13). [Conclusion] The bovine ciliary muscle possesses a voltage-dependent sodium channel similar to those distributed in neurones and skeletal muscle. [Jpn J Physiol 55 Suppl:S138 (2005)]
