抄録
We examined the kinetic properties of gap junction channels (GJCs) responsible for the outward rectification and low-pass filtering. When dual whole-cell recordings were made from two mesencephalic trigeminal neurons coupled via GJCs, both depolarizing and hyperpolarizing responses evoked by current pulse injections into one cell under current-clamp conditions were markedly attenuated in the other cell. Depolarizing responses were more markedly attenuated in the other cell than hyperpolarizing responses, suggesting the nature of outward rectification of GJCs. Furthermore, the action potential was more markedly attenuated than the sustained depolarization, suggesting the low-pass filter property of GJCs. When current responses to the symmetrical positive- and negative-going ramp pulses were recorded by using 0.2 mM EGTA internal solution, the maximal outward currents evoked by negative-going ramp pulses were smaller than those to positive-going ramp pulses. This became more prominent when the ramp rate was decreased. However, when 10 mM BAPTA was used instead of EGTA, the difference in the current amplitude became less clear. These results suggest that the apparent outward rectification may be mediated by the voltage dependence of the junctional conductance, which may be modified by [Ca2+]i changes. Furthermore, it is likely that the apparent nature as low-pass filter may be mediated by the time-dependent activation of GJCs, which is determined by the channel-opening rate constant that decreases with membrane depolarization. [Jpn J Physiol 55 Suppl:S138 (2005)]
