Subcellular gradients of intracellular free calcium concentration in isolated lacrimal acinar cells.
The spatial distribution of intracellular free calcium concentration ([Ca2+]i) was measured in small clusters of isolated rat lacrimal acinar cells by imaging the fluorescence of the Ca(2+)-sensitive dye fura-2. In the absence of extracellular Ca2+, stimulation with acetylcholine (ACh) caused an increase in [Ca2+]i, due to release of intracellular Ca2+ stores, which was maximal at the luminal pole of the cell. In contrast, the organellar Ca(2+)-ATPase inhibitor 2,5-di(tert-butyl)-hydroquinone caused an increase in [Ca2+]i, which was most marked in the basolateral region of the cell. When the cells were stimulated with ACh in a medium containing Ca2+, the gradients of [Ca2+]i (with [Ca2+]i most elevated at the luminal pole) were maintained for the duration of agonist stimulation. The possible implications of these results concerning the location and identity of intracellular Ca2+ stores, and the location of the sites that underlie agonist-stimulated Ca2+ influx, are considered. In particular, it seems likely that intracellular inositol-1,4,5-trisphosphate (InsP3) binding sites may be concentrated in the luminal region of the cell. It is not clear, however, whether this implies that there is a distinct luminally located InsP3-sensitive organelle.
Elliott
A C
AC
Department of Physiological Sciences, University of Manchester, UK.
Cairns
S P
SP
Allen
D G
DG
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006873:Hydroquinones / Q000494:pharmacology*; D017136:Ion Transport / Q000187:drug effects; D007765:Lacrimal Apparatus / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D006873:Hydroquinones; C018855:2-tert-butylhydroquinone; D000109:Acetylcholine; D002118:Calcium