Ion channels in the basolateral membrane of intralobular duct cells of mouse mandibular glands.

We have used single-channel patch-clamp techniques to study the ion channels in the basolateral membranes of intralobular duct cells from the mouse mandibular gland. In 39% of cell-attached patches, we observed a K+ channel that had an inwardly rectifying current/voltage (I/V) relation with a maximum slope conductance of 123 +/- 9 pS (n = 12) and a zero current potential of +49.4 +/- 3.4 mV (n = 5) relative to the resting cell potential. The selectivity sequence of this channel, as estimated by zero current potential measurements, was: K+ (1) > Rb+ (0.38) > NH4+ (< 0.34), Cs+ (< 0.16) > Na+ (< 0.028). The activity of the channel was not affected by changes in membrane potential, nor was it affected by changes in the free Ca2+ concentration on the cytosolic side of inside-out excised patches in the range 1 nmol/l to 1 mumol/l. In 38% of cell-attached patches we observed a second K+ channel type with a maximum slope conductance of 62 +/- 3 pS (n = 12) and an inwardly rectifying I/V relation. The selectivity sequence of this channel was K+ (1) > Rb+ (< 0.5) > NH4+ (< 0.2) > Na+ (< 0.09). The activity of this channel type was not affected by changes in membrane potential. In 18% of excised patches, we also observed a non-selective cation channel that was not demonstrable in cell-attached patches. It had a slope conductance of 22 +/- 2 pS (n = 6) and was blocked by the non-selective cation channel blocker, flufenamate (10 mumol/l).(ABSTRACT TRUNCATED AT 250 WORDS)