[$Ca^{2+}-activated\;K^+$ Currents of Pancreatic Duct Cells in Guinea-pig

There are numerous studies on transepithelial transports in duct cells including $Cl^-$ and/or $HCO_3^-$. However, studies on transepithelial $K^+$ transport of normal duct cells in exocrine glands are scarce. In the present study, we examined the characteristics of $K^+$ currents in single duct cells isolated from guinea pig pancreas, using a whole-cell patch clamp technique. Both $Cl^-$ and $K^+$ conductance were found with KCI rich pipette solutions. When the bath solution was changed to low $Cl^-$, reversal potentials shifted to the negative side, $-75{\pm}4\;mV$, suggesting that this current is dominantly selective to $K^+$. We then characterized this outward rectifying $K^+$ current and examined its $Ca^{2+}$ dependency. The $K^+$ currents were activated by intracellular $Ca^{2+}$. 100 nM or 500 nM $Ca^{2+}$ in pipette significantly (P<0.05) increased outward currents (currents were normalized, $76.8{\pm}7.9\;pA$, n=4 or $107.9{\pm}35.5\;pA$, n=6) at +100 mV membrane potential, compared to those with 0 nM $Ca^{2+}$ in pipette $(27.8{\pm}3.7\;pA,\;n=6)$. We next examined whether this $K^+$ current, recorded with 100 nM $Ca^{2+}$ in pipette, was inhibited by various inhibitors, including $Ba^{2+}$, TEA and iberiotoxin. The currents were inhibited by $40.4{\pm}%$ (n=3), $87.0{\pm}%$ (n=5) and $82.5{\pm}%$ (n=9) by 1 mM $Ba^{2+}$, 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 $Ca^{2+}$. The $K^+$ current may play a role in secretory process, slnce recycling of $K^+$ is critical for the initiation and sustaining of $CI^-$ or $HCO_3^-$ secretion in these cells.