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

Abstract.

Previous studies of the whole-cell K⁺ conductance suggest the presence of inwardly rectifying K⁺ 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 µM and 1.1±0.2 µM 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 slope 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_ir2.1, K_ir2.3 and K_ir7.1 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.