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Intracellular Free Calcium Measured with Calcium-Selective Microelectrodes from Salivary Gland Cells of the Snail Planorbis Corneus
1 Physiological Institute, University of Munich, Pettenkoferstrasse 12, 8000 Munich 2, West Germany
Abteilung Pharmakologie, E. Merck AG, Frankfurterstrasse 250, 6100 Darmstadt 1, West Germany
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.24x10-7moll-1 (S.D. ±0.84x10-7moll-1), while the mean EM was -67.1 ±4.1mV. 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 2.9x10-7moll-1 (S.D.±1.0x10-7moll-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.
Key words: salivary gland cells, intracellular free Ca2+, calcium-selective microelectrode, snail, Planorbis corneus, acetylcholine, lithium
Accepted on November 6, 1985
