Effects of secretagogues on intracellular free calcium and magnesium concentrations in rat pancreatic acinar cells.
1. Rat pancreatic acinar cells were loaded with Fura 2 AM or Magfura AM and levels of cytosolic Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) were observed. 2. Addition of acetylcholine (ACh) evoked a transient rise in [Ca2+]i. The component of the rise dependent on extracellular Ca2+ sources, but not intracellular sources, was seen to be enhanced when both ACh and 5 mM Ca2+ were present in the medium. In the presence of elevated extracellular Mg2+ (10 mM) and ACh both components of the Ca2+ transient were inhibited. 3. Both GTP gamma S and fluoroaluminate, which can directly stimulate G-proteins, evoked a transient rise in [Ca2+]i in acinar cells. These responses were inhibited in the presence of elevated Mg2+. 4. Resting [Mg2+]i was seen to be 1.36 mM +/- 0.08 (n = 29) for cells in normal medium, 1.8 mM +/- 0.08 (n = 6) in elevated Mg2+ medium and 0.93 mM +/- 0.02 (n = 5) in cells bathed and Mg(2+)-free medium. Addition of ACh led to reductions in [Mg2+]i in cells bathed in normal medium and Mg(2+)-free medium but not elevated Mg2+ medium. 5. It is concluded that levels of extracellular Mg2+ strongly influence [Mg2+]i and [Ca2+]i mobilization during ACh-evoked responses. Mg2+ does not appear to be exerting its effects by influencing receptor-agonist interactions or by competing with Ca2+ at extracellular sites of Ca2+ uptake.
Lennard
R
R
Department of Applied Biology, University of Central Lancashire, Preston, England.
Singh
J
J
D000109:Acetylcholine / Q000494:pharmacology*; D000535:Aluminum / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D005456:Fluorescent Dyes; D005461:Fluorine / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D005456:Fluorescent Dyes; C053629:fluoroaluminum; D005461:Fluorine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000535:Aluminum; D008274:Magnesium; D000109:Acetylcholine; D002118:Calcium