Salivary gland cells of the pond snail Planorbis corneus produce a biphasic depolarizing-hyperpolarizing electrical response following the application of acetylcholine (ACh). Ion-substitution experiments have indicated that the depolarizing phase of the ACh response is produced at least in part by an influx of Na +, while the subsequent hyperpolarization results from the activity of an electrogenic Na+/K+ pump (Barber, 1985). It is not known, however, whether other species of ions also participate in this response, and the role of the extracellular medium as a source of the ions which compose the salivary secretion remains unclear. For these reasons the present study with ion-selective microelectrodes was undertaken in order to measure directly the shifts in extracellular ion concentrations which take place during stimulation with ACh.
Salivary glands were isolated from specimens of Planorbis corneus as previously described (Barber, 1985). Pairs of glands were...
