Amplification of the thapsigargin-evoked increase in the cytosolic free Ca2+ concentration by acetylcholine in acutely isolated mouse submandibular acinar cells.
The intracellular Ca2+ concentration was measured in single, acutely isolated, mouse submandibular acinar cells loaded with fura-2 AM. All experiments were performed in the absence of extracellular Ca2+ in order to eliminate Ca2+ influx. The microsomal ATPase inhibitor, thapsigargin, was used to release Ca2+ from intracellular stores and simultaneously prevent re-uptake into the stores. Sequential application of thapsigargin (2 microM) and the Ca2+ ionophore ionomycin (500 nM) indicated that thapsigargin was able to mobilize practically all intracellular Ca2+. Furthermore, in comparison with results obtained following inhibition of the plasma membrane Ca(2+)-ATPase by La3+ (2 mM), it may be shown that slowly unloading the intracellular Ca2+ stores using thapsigargin does not normally cause a massive, cytotoxic, increase in the cytosolic Ca2+ concentration, because Ca2+ is rapidly extruded from the cell across the plasma membrane. Application of a submaximal dose of acetylcholine (500 nM) during the rising phase of the response to thapsigargin caused a 3-4-fold increase in the amplitude of the rise in the cytosolic Ca2+ concentration without any significant alteration of the time course of the response. As thapsigargin alone is capable of mobilizing all releasable Ca2+, this increase in amplitude is most likely the result of inhibition of the Ca2+ extrusion process by acetylcholine.
Smith
P M
PM
Department of Clinical Dental Sciences, University of Liverpool, UK.
Reed
H E
HE
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004357:Drug Synergism; D066298:In Vitro Techniques; D017136:Ion Transport; D007700:Kinetics; D008297:Male; D051379:Mice; D013363:Submandibular Gland / Q000187:drug effects* / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D013729:Terpenes; D019284:Thapsigargin; D000109:Acetylcholine; D002118:Calcium