Functional homogeneity of the non-mitochondrial Ca2+ pool in intact mouse lacrimal acinar cells

• Published in: The Journal of biological chemistry 1992-09, Vol.267 (26), p.18382-18386
• Main Authors: G J Bird, J F Obie, J W Putney, Jr
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Calcium - metabolism; Cations, Divalent; Cell physiology; Cells, Cultured; Fluorescence; Fundamental and applied biological sciences. Psychology; Fura-2; Inositol 1,4,5-Trisphosphate - metabolism; Inositol Phosphates - metabolism; Ionomycin - pharmacology; Lacrimal Apparatus - cytology; Lacrimal Apparatus - drug effects; Lacrimal Apparatus - metabolism; Male; Methacholine Chloride - pharmacology; Mice; Miscellaneous; Mitochondria - metabolism; Molecular and cellular biology; Ruthenium Red - chemistry; Saponins - chemistry; Terpenes - pharmacology; Thapsigargin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)36973-X

In the absence of extracellular Ca2+, treatment of mouse lacrimal acinar cells with maximal concentrations of methacholine released Ca2+ from intracellular stores. No additional Ca2+ was mobilized by subsequent application of the intracellular Ca(2+)-ATPase inhibitor, thapsigargin, the stable inositol 1,4,5-trisphosphate ((1,4,5)IP3) analog, inositol 2,4,5-trisphosphate ((2,4,5)IP3) (by microinjection), or the Ca2+ ionophore, ionomycin. However, following prolonged activation of cells by methacholine in the presence of extracellular Ca2+, Ca2+ accumulated into a pool which was released by ionomycin but not by thapsigargin. This latter accumulation was blocked by prior microinjection of ruthenium red, indicating that it represents mitochondrial uptake. In saponin-permeabilized lacrimal cells, two Ca(2+)-sequestering pools were detected: (i) a ruthenium red-sensitive, thapsigargin-insensitive pool, presumed to be the mitochondria; and (ii) a ruthenium red-insensitive, thapsigargin-sensitive pool. Only the thapsigargin-sensitive pool accumulated Ca2+ at concentrations similar to those in unstimulated cells. The thapsigargin-sensitive Ca2+ pool was sensitive to (1,4,5)IP3; however, in contrast to findings in intact cells, only 44% of this pool was releasable by (1,4,5)IP3 or (2,4,5)IP3. These data indicate that, in intact lacrimal acinar cells, all exchangeable (ionomycin-sensitive) Ca2+ residues in a pool which responds homogeneously to agonists, (1,4,5)IP3, and thapsigargin. Prolonged elevation of [Ca2+]i results in Ca2+ accumulation into a second, ruthenium red-sensitive pool, presumably mitochondria. Finally, permeabilization of the cells fragments the non-mitochondrial pool, resulting in two pools, one sensitive and one insensitive to (1,4,5)IP3.