Ca<SUP>2&#8290;</SUP>-activated K<SUP>&#8290;</SUP> Currents of Pancreatic Duct Cells in Guinea-pig

Ca<SUP>2&#8290;</SUP>-activated K<SUP>&#8290;</SUP> Currents of Pancreatic Duct Cells in Guinea-pig

There are numerous studies on transepithelial transports in duct cells including Cl<SUP>&#8291;</SUP> and/or HCO<SUB>3</SUB><SUP>&#8291;</SUP>. However, studies on transepithelial K<SUP>&#8290;</SUP> transport of normal duct cells in exocrine glands are scarce. In the present study, we examined the characteristics of K<SUP>&#8290;</SUP> currents in single duct cells isolated from guinea pig pancreas, using a whole-cell patch clamp technique. Both Cl<SUP>&#8291;</SUP> and K<SUP>&#8290;</SUP> conductance were found with KCl rich pipette solutions. When the bath solution was changed to low Cl<SUP>&#8291;</SUP>, reversal potentials shifted to the negative side, &#8291;75&#8273;4 mV, suggesting that this current is dominantly selective to K<SUP>&#8290;</SUP>. We then characterized this outward rectifying K<SUP>&#8290;</SUP> current and examined its Ca<SUP>2&#8290;</SUP> dependency. The K<SUP>&#8290;</SUP> currents were activated by intracellular Ca<SUP>2&#8290;</SUP>. 100 nM or 500 nM Ca<SUP>2&#8290;</SUP> in pipette significantly (P＜0.05) increased outward currents (currents were normalized, 76.8&#8273;7.9 pA, n=4 or 107.9&#8273;35.5 pA, n=6) at &#8290;100 mV membrane potential, compared to those with 0 nM Ca<SUP>2&#8290;</SUP> in pipette (27.8&#8273;3.7 pA, n=6). We next examined whether this K<SUP>&#8290;</SUP> current, recorded with 100 nM Ca<SUP>2&#8290;</SUP> in pipette, was inhibited by various inhibitors, including Ba<SUP>2&#8290;</SUP>, TEA and iberiotoxin. The currents were inhibited by 40.4&#8273;% (n=3), 87.0&#8273;% (n=5) and 82.5&#8273;% (n=9) by 1 mM Ba<SUP>2&#8290;</SUP>, 5 mM TEA and 100 nM iberiotoxin, respectively. Particularly, an almost complete inhibition of the current by 100 nM iberiotoxin further confirmed that this current was activated by intracellular Ca<SUP>2&#8290;</SUP>. The K<SUP>&#8290;</SUP> current may play a role in secretory process, since recycling of K<SUP>&#8290;</SUP> is critical for the initiation and sustaining of Cl<SUP>&#8291;</SUP> or HCO<SUB>3</SUB><SUP>&#8291;</SUP> secretion in these cells.