Differences in intracellular CA2+ stores of submandibular cells of adult and newborn rats.
The intracellular Ca2+ stores of submandibular acinar cells of adult and newborn rats were compared by measuring changes in cytosolic Ca2+ ([Ca2+]i) with the Ca2+-sensitive fluorescent probe, fura-2, in intact cells and 45Ca2+ release in permeabilized cells. In cells of adult rats, acetylcholine (ACh) and thapsigargin (TG) elicited, respectively, a 105% and 125% net increase in [Ca2+]i in Ca2+-free medium. In cells of newborn animals, the ACh-induced [Ca2+]i increase (218%) was larger; but the TG-induced increase was significantly smaller (77%), suggesting that the TG-sensitive Ca2+ pump of the store is less developed, abundant, or responsive in these cells. After ACh or TG, ionomycin elicited a further Ca2+ release. Ionomycin by itself completely discharged the ACh- and TG-sensitive store in cells of mature glands but not in cells of immature glands, suggesting a further difference in the distribution of the agonist and ionomycin sensitivities in the two types of cells. After exposure to ACh + ionomycin or TG + ionomycin, collapsing the intracellular pH gradient with monensin caused a third and large Ca2+ release (262% and 289%, respectively) in cells of adult rats, but a significantly smaller release (96%, P < 0.001, and 57%, P < 0.001, respectively) in cells of newborn rats, suggesting that a third, IP3-insensitive acidic store is significantly smaller in cells of immature glands. In permeabilized and 45Ca2+-loaded cells, inositol-1,4,5-trisphosphate (IP3, 5 microM) induced an identical 45Ca2+ release (34% and 33%, respectively) in both types of cells, but TG induced a significant smaller 45Ca2+ release in cells of immature glands (15%) than in cells of mature glands (33%). Monensin discharged <10% of loaded 45Ca2+ in both types of cells, indicating that the radiotracer was not loaded into the monensin-sensitive store. These results suggest that in cells of immature glands: (1) the TG-sensitive Ca2+ pump of the IP3-sensitive store is not well developed; (ii) the IP3-sensitive store is not completely discharged by ionomycin; and (iii) an acidic store likely to be associated with secretory granules is also underdeveloped and of a smaller size than in cells of mature glands.
Martinez
J R
JR
Department of Pediatrics, University of Texas Health Science Center at San Antonio, 78284, USA.
Wells
J
J
Puente
S
S
Willis
S
S
Zhang
G H
GH
D000109:Acetylcholine / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008985:Monensin / Q000494:pharmacology; D051381:Rats; D013363:Submandibular Gland / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007476:Ionophores; D015759:Ionomycin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D008985:Monensin; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium