There are some evidences that K efflux evoked by muscarinic stimulation is not mainly mediated by large conductance K (BK) channels in salivary gland. In this experiment, we therefore characterised non BK channels in rat submandibular gland acinar cells and examined the possibility of agonist effect on this channel using a patch clamp technique. Two types of K channels were observed in these cells. BK channels were observed in 3 cells from total 6 cells and its average conductance was 152⁑7 pS (n=3). The conductance of the another types of K channel was estimated as 71⁑7 pS (n=6). On the basis of the conductance of this channel, we defined this channel as intermediate conductance K (IK) channels, which were observed from all 6 cells we studied. When we increased Ca2 concentration of the bath solution in inside-out mode, the IK channel activity was greatly increased, suggesting this channel is Ca2 sensitive. We next examined the effect of carbachol (CCh) and isoproterenol on the activity of the IK channels. 105 M isoproterenol significantly increased the open probability (Po) from 0.08⁑0.02 to 0.21⁑0.03 (n=4, P＜0.05). Application of 105 M CCh also increased Po from 0.048⁑0.03 to 0.55⁑0.33 (n=5, P＜0.05) at the maximum channel activity. The degree of BK channel activation induced by the same concentration of CCh was lower than that of IK channels; Po value was 0.011⁑0.003 and 0.027⁑0.005 in control and during CCh stimulation (n=3), respectively. The result suggests that IK channels exist in salivary acinar cells and its channel activity is regulated by muscaricinic and β- adrenergic agonist. We conclude that IK channels also play a putative role in secretion as well as the BK channels in rat submandibular gland acinar cells.
