Intracellular Free Calcium Measured with Calcium-Selective Microelectrodes From Salivary Gland Cells of the Snail Planorbis Corneus

Abstract

ABSTRACT Double-barrelled Ca2+-selective microelectrodes have been used to make simultaneous measurements of the intracellular concentration of free Ca2+ ([Ca2+]i) and membrane potential (EM) from single salivary gland acinar cells of the pond snail Planorbis corneus. The mean [Ca2+]i recorded from nine cells in unstimulated glands was l·24×10−7moll−1 (S.D. ± 0·84×10−7moll−1), while the mean EM was −67·1 ±4·1 mV. The equilibrium potential for Ca2+ in these cells was calculated to be +132mV. Stimulating the glands with 10−4moll−1 acetylcholine (ACh) produced a simultaneous depolarization of EM and an increase in [Ca2+]i by 2·9×10−7moll−1 (S.D. ± 10× 10−7moll−1, N= 12), followed by a transient hyperpolarization of EM and the restoration of [Ca2+]i to its original level. ACh-induced increases in [Ca2+]i were abolished, or much reduced in size, after the removal of extracellular Ca2+, though the EM response to ACh was unaffected in Ca2+-free saline. This finding indicates that the application of ACh leads to an influx of Ca2+ from the medium bathing the glands. Li+ caused an increase in the size of the ACh-induced elevation in the Ca2+ signal and inhibited the recovery of [Ca2+]i following stimulation. The implications of this observation are discussed.