Inwardly rectifying K+ channels in the basolateral membrane of rat pancreatic acini

Previous studies of the whole-cell K+ conductance suggest the presence of inwardly rectifying Kf channels (K-ir) in rat pancreatic acini (RPAs). Here we investigate the properties of K-ir of RPAs using patch-clamp techniques. The whole-cell current-to-voltage relationship of Freshly isolated RPAs was steeper for inward currents than for outward currents when the extracellular K+ concentration ([K+](o)) was raised. With a high [K+](o) (145 mM), external application of Ba2+ and Cs+ blocked the inward K+ current in a voltage-dependent manner. The apparent IC50 of Ba2+ was 8.5+/-1.9 muM and 1.1+/-0.2 muM at -70 mV and -130 mV, respectively (n=5). The IC50 of Cs+ was 3.5+/-1.1 mM and 0.2+/-0.1 mM at -60 mV and -120 mV, respectively (n=4). Application of Ba2+ (0.1 mM) to the extracellular solution reversibly depolarized RPAs from -43+/-1.1 mV to -37+/-1.2 mV (n=20). In the cell-attached configuration with 145 mM KCl in the pipette solution, we observed inwardly rectifying channels with a high open probability (P-o) of 0.85+/-0.02 (n=6) and a slops conductance (G(s)) of 30+/-2.8 pS (n=13). The same type of channel was observed in the outside-out patch. We could also observe a very small conductance K+ channel which was resistant to 0.1 mM Ba2+ and did not show inward rectification (n=11). RT-PCR analysis of RPA confirmed the presence of transcripts for K(ir)2.1, K(ir)2.3 and K(ir)7.1 subfamilies as molecular candidates for the observed channels. The above results demonstrate the presence of K-ir channels in the basolateral membrane of the RPA, which may be important for the K+ recycling process during electrolyte secretion as well as for maintaining a hyperpolarized membrane.