Depletion of ryanodine-sensitive Ca2+ store activates Ca2+ entry in rat submandibular gland acinar cells.
The existence of ryanodine-sensitive Ca2+ stores and their role in the Ca2+ entry mechanism were examined in the rat submandibular gland acinar cells, using the microfluorimetry of intracellular Ca2+ concentration ([Ca2+]i). In the presence of thapsigargin, a Ca(2+)-ATPase inhibitor of inositol (1, 4, 5) triphosphate (InsP3)-sensitive Ca2+ stores, caffeine caused an increase in [Ca2+]i, which was inhibited by treatment with ryanodine (a ligand to the Ca(2+)-induced Ca2+ release channels). In the cells treated with ryanodine, 1 mM Ca2+ addition to a Ca(2+)-free solution caused a marked increase in [Ca2+]i, which was eliminated by application of Ni2+ or SK & F 96365, suggesting a Ca2+ entry triggered by ryanodine. The maximal change in the net increase in [Ca2+]i caused by the ryanodine-coupled Ca2+ entry, was 104.0 +/- 16.0 nM, which intense was caused by 10 microM ryanodine. Emptying the InsP3-sensitive stores by treatment with thapsigargin also caused Ca2+ entry, which maximally changed [Ca2+]i by 349.6 +/- 15.1 nM. Ten mumol/liter ryanodine was confirmed to cause a release of 45Ca2+ from the parotidic microsomal fraction enriched in endopalsmic reticulum. We propose that ryanodine-sensitive Ca2+ stores are present in rat submandibular gland acinar cells. We further propose that release of Ca2+ from the ryanodine-sensitive stores, which means eventually depletion of the ryanodine-sensitive Ca2+ stores, can activate the Ca2+ entry. The ability for Ca2+ entry coupled with the ryanodine-sensitive Ca2+ stores seems to be about 30% of the ability for Ca2+ entry coupled with the thapsigargin-sensitive Ca2+ stores.
Fukushi
Y
Y
Department of Physiology, Tohoku University School of Medicine, Sendai, Japan.
Ozawa
T
T
Nishiyama
A
A
Kase
H
H
Wakui
M
M
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology*; D013363:Submandibular Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D002132:Calcium Radioisotopes; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D010726:Phosphodiesterase Inhibitors; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium