Chloride channels in the luminal membrane of rat pancreatic acini

Pancreatic acini secret Na+, Cl- and H2O in response to secretagogues such as acetylcholine. Cl- channels in the luminal membrane are a prerequisite for this secretion. The properties of the corresponding conductance have previously been examined using whole-cell recordings. The present study attempts to examine the properties of the single channels in cell-attached and cell-free excised patches from the luminal membrane. To this end the pipettes were filled with an N-methyl-D-glucamine (NMDG+) chloride-gluconate solution. The voltage-clamp range was chosen to be pipette positive (cell negative, -60 to -130 mV) in order to increase the driving force for outward Cl- currents. Under resting conditions cell attached luminal patches had very few single-channel currents (12 out of 45 experiments). Their incidence was sharply increased by carbachol (CCH, 1 micromol/l) in 41 out of 45 experiments. The single-channel conductance of these channels was 1.97 +/- 0.05 pS. The properties of these channels in excised patches were examined further: their single-channel conductance was 2.2 +/- 0.07 pS (n = 59) and their conductance selectivity was I- > Br- > Cl- >> gluconate. None of the typical Cl- channel blockers (DIDS, NPPB, glibenclamide 100 micromol/l) blocked these channels. It is concluded that the luminal membrane of the rat pancreatic acinus possesses Cl- channels with very low conductance which are activated by carbachol.