Acetylcholine-evoked increase in the cytoplasmic Ca2+ concentration and Ca2+ extrusion measured simultaneously in single mouse pancreatic acinar cells.
The intracellular free Ca2+ concentration ([free Ca2+]i) was measured simultaneously with the Ca2+ extrusion from single isolated mouse pancreatic acinar cells placed in a microdroplet of extracellular solution using the fluorescent probes fura-2 and fluo-3. The extracellular solution had a low total calcium concentration (15-35 microM), and acetylcholine (ACh), applied by microionophoresis, therefore only evoked a transient elevation of [free Ca2+]i lasting about 2-5 min. The initial sharp rise in [free Ca2+]i from about 100 nM toward 0.5-1 microM was followed within seconds by an increase in the total calcium concentration in the microdroplet solution ([Ca]o). The rate of this rise of [Ca]o was dependent on the [free Ca2+]i elevation, and as [free Ca2+]i gradually decreased Ca2+ extrusion declined with the same time course. Ca2+ extrusion following ACh stimulation was not influenced by removal of all Na+ in the microdroplet solution indicating that the Ca2+ extrusion is not mediated by Na(+)-Ca2+ exchange but by the Ca2+ pump. The amount of Ca2+ extruded during the ACh-evoked transient rise in [free Ca2+]i corresponded to a decrease in the total intracellular Ca concentration of about 0.7 mM which is close to previously reported values (0.5-1 mM) for the total concentration of mobilizable calcium in these cells. Our results therefore demonstrate directly the ability of the Ca2+ pump to rapidly remove the large amount of Ca2+ released from the intracellular pools during receptor activation.
Tepikin
A V
AV
Medical Research Council Secretory Control Research Group, University of Liverpool, United Kingdom.
Voronina
S G
SG
Gallacher
D V
DV
Petersen
O H
OH
D000109:Acetylcholine / Q000494:pharmacology*; D000814:Aniline Compounds; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D005456:Fluorescent Dyes; D016257:Fura-2; D051379:Mice; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014966:Xanthenes
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D011956:Receptors, Cell Surface; D014966:Xanthenes; C059715:Fluo-3; D012964:Sodium; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2