Pancreatic acinar cells: the effect of carbon dioxide, ammonium chloride and acetylcholine on intercellular communication.

Abstract

1. Segments of mouse pancreatic or exorbital lacrimal gland were superfused with saline solutions. Under visual control two micro-electrodes were inserted into neighbouring cells within the same acinus or into neighbouring acini. Cell to cell electrical coupling was assessed by injecting rectangular current pulses through one electrode and measuring the electrotonic potential change in the same cell (V(1)) and in the neighbouring cell (V(2)). Acetylcholine (ACh) was added locally to impaled acini by micro-ionophoresis from an extracellular micropipette.2. Exposure of the tissues to a Krebs solution equilibrated with 100% CO(2) caused a rapid increase in the size of electrotonic potential changes in the current injection cell and disappearance of the electrotonic potential changes in a neighbouring acinus or cell. This electrical uncoupling of previously coupled cells was rapidly reversible upon return to a solution equilibrated with 95% O(2) and 5% CO(2).3. Reduction of electrical intercellular coupling was also obtained using smaller CO(2) concentrations (50, 20 or 10%). In these cases the effects developed more slowly and were less dramatic. Reducing the extracellular HCO(3) concentration enhanced the uncoupling effect of 10 or 20% CO(2). However, weak uncoupling effects were still observed using 10 or 20% CO(2) in combination with a high bicarbonate concentration maintaining a constant extracellular pH (7.4).4. Reductions in extracellular pH (down to 5.5) achieved by varying combinations of Tris base and Tris HCl had no effect on electrical coupling. Brief periods of anoxia (100% N(2)) also had no effect.5. Exposure to 20% CO(2) markedly enhanced the uncoupling effect of a brief ionophoretic pulse of ACh.6. Exposure of the tissue to 10 mM-NH(4)Cl, a procedure expected to increase the intracellular pH, counteracted the uncoupling effect of ACh. During sustained uncoupling caused by a sustained ACh stimulation a brief period of exposure to NH(4)Cl caused an immediate and fully reversible recoupling.7. It is concluded that variations in intracellular pH have marked effects on the electrical coupling between neighbouring cells in the pancreatic and lacrimal acinar tissue.