Since the δ-opioid receptors were first expressed on Xenopus oocyte and mammalian cells in 1992, signal transduction mechanism between δ-opioid receptors and ionic channels have been inverstigated by many researchers.
Here we report the ionic channels activated or inactivated by δ-opioid receptors expressed on HEK293 cell. Because of clustering of HEK293 cells due to electical coupling, the ionic currents were recorded in the cell attached configuration instead of whole cell recording. To suppress the CI` current, CI` was replaced with impermeant anion gluconate and also to block the small conductance Ca^(2+) dependent K^(+) channels and Ca^(2+) channels, apamin (0.1 ㎛) and Cd^(2+) (50 ㎛) were added to the pipette solution.
Under these conditions, ~30 and ~90 pS unitary outward currents which showed the outward rectification were recorded in HEK293 cells. When the δ-opioid receptor was stimulated with δ-opioid specific agonist DPDPE (0.1 ㎛) the open probability of ~90 pS channel increased but that of ~30 pS channel decreased. For characterization of these ionic channels, 4-aminopyridine (0.3 ㎛) and glibenclamide (50 ㎛) were added to bath solution. The open probability of ~30 and ~90 pS channels were not changed by glibenclamide whereas the open probability of ~90 pS channel decreased by 4-aminopyridine.
In summary it is strongly suggest that ~30 pS and ~90 pS ionic channels recorde in the present study are delayed rectifier K^(+) and maxi K^(+) channels, respectively.
|