Calcium pools in Ehrlich carcinoma cells. A major, high affinity Ca2+ pool is sensitive to both inositol 1,4,5-trisphosphate and thapsigargin.
To investigate the presence and the size of different non-mitochondrial Ca2+ pools of Ehrlich ascites tumor cells (EATCs), digitonin-permeabilized cells were allowed to accumulate Ca2+ in the presence of mitochondrial inhibitors and treated with the reticular Ca(2+)-ATPase inhibitor thapsigargin, IP3 and the Ca2+ ionophore A23187. Emptying of thapsigargin-sensitive Ca2+ stores prevented any Ca2+ release by IP3, and, after IP3 addition, little or no Ca2+ was released by thapsigargin. In both instances, a further Ca2+ release was accomplished by A23187. The IP3-thapsigargin-sensitive pool and the residual A23187-sensitive one corresponded to approximately 60 and 37% of non-mitochondrial stored Ca2+, respectively. In intact EATCs, IP3-dependent agonists and thapsigargin discharged Ca2+ pools almost completely overlapping, and A32187 released a minor residual Ca2+ pool. The IP3-insensitive pool appeared to have a relatively low affinity for Ca2+ (below 600 nM). The high affinity, IP3-sensitive Ca2+ pool was discharged in a 'quantal' manner following step additions of sub maximal [IP3], and the IP3-induced fractional Ca2+ release was more marked at higher concentrations of stored (luminal) Ca2+, The IP3-sensitive Ca2+ pool appeared to be devoid of the Ca(2+)-activated Ca2+ release channel since caffeine did not released any Ca2+ in intact and permeabilized EATCs, and Western blot analyses of EATC microsomal membranes failed to detect any known ryanodine receptor isoform.
Istituto di Patologia Generale, University of Siena, Italy.
A
A
Gamberucci
R
R
Fulceri
P
P
Tarroni
R
R
Giunti
P
P
Marcolongo
V
V
Sorrentino
A
A
Benedetti
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002273:Carcinogens; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D051379:Mice; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D014407:Tumor Cells, Cultured
D002273:Carcinogens; D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium