Swelling-induced Ca2+ release from intracellular calcium stores in rat submandibular gland acinar cells.
The effects of osmotically-induced cell swelling on cytoplasmic free Ca2+ concentration ([Ca2+]i) were studied in acinar cells from rat submandibular gland using microspectrofluorimetry. Video-imaging techniques were also used to measure cell volume. Hypotonic stress (78% control tonicity) caused rapid cell swelling reaching a maximum relative volume of 1.78 +/- 0.05 (n = 5) compared to control. This swelling was followed by regulatory volume decrease, since relative cell volume decreased significantly to 1.61 +/- 0.08 (n = 5) after 10 min exposure to hypotonic medium. Osmotically induced cell swelling evoked by medium of either 78% or 66% tonicity caused a biphasic increase of [Ca2+]i. The rapid phase of this increase in [Ca2+]i was due to release of Ca2 + from intracellular stores, since it was also observed in cells bathed in Ca2+-free solution. The peak increase of [Ca2+]i induced by cell swelling was 3.40 +/- 0.49 (Fura-2 F340/F380 fluorescence ratio, n = 11) and 3.17 +/- 0.43 (n = 17) in the presence and the absence of extracellular Ca2+, respectively, corresponding to an absolute [Ca2+]i of around 1 microm. We found that around two-thirds of cells tested still showed some swelling-induced Ca2+ release (SICR) even after maximal concentrations (10(-5) M - 10(-4) M) of carbachol had been applied to empty agonist-sensitive intracellular Ca2+ stores. This result was confirmed and extended using thapsigargin to deplete intracellular Ca2+ pools. Hypotonic shock still raised [Ca2+]i in cells pretreated with thapsigargin, confirming that at least some SICR occurred from agonist-insensitive stores. Furthermore, SICR was largely inhibited by pretreatment of cells with carbonyl cyanide m-cholorophenyl hydrazone (CCCP) or ruthenium red, inhibitors of mitochondrial Ca2+ uptake. Our results suggest that the increase in [Ca2+]i, which underlies regulatory volume decrease in submandibular acinar cells, results from release of Ca2+ from both agonist-sensitive and mitochondrial Ca2+ stores.
Park
K
K
Department of Physiology, College of Dentistry, Seoul National University, Korea.
Lee
S
S
Elliott
A C
AC
Kim
J S
JS
Lee
J H
JH
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000008:administration & dosage; D048429:Cell Size; D018679:Cholinergic Agonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009994:Osmolar Concentration; D009995:Osmosis / Q000502:physiology*; D009997:Osmotic Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012430:Ruthenium Red / Q000008:administration & dosage; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013363:Submandibular Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D018679:Cholinergic Agonists; D012430:Ruthenium Red; D002110:Caffeine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D019284:Thapsigargin; D002217:Carbachol; D002118:Calcium