Mobilization of calcium by inositol trisphosphates from permeabilized rat parotid acinar cells. Evidence for translocation of calcium from uptake to release sites within the inositol 1,4,5-trisphosphate- and thapsigargin-sensitive calcium pool.
D-myo-Inositol (1,4,5)-trisphosphate ((1,4,5)IP3)-induced Ca2+ release and subsequent Ca2+ reuptake were investigated in saponin-permeabilized rat parotid acinar cells. Following the rapid release of Ca2+ by (1,4,5)IP3, Ca2+ was resequestered. The sequential addition of submaximal concentrations of (1,4,5)IP3 resulted in sequential Ca2+ release. However, when the cells were challenged with the poorly metabolized (1,4,5)IP3 analogues, (1,4,5)IPS3 or (2,4,5)IP3, or under conditions where the metabolism of authentic (1,4,5)IP3 was reduced, Ca2+ reuptake again occurred, but sequestered Ca2+ was not released by subsequent additions of (1,4,5)IP3. The sequestered Ca2+ was, however, released by thapsigargin, an agent which inhibits active Ca2+ uptake into the (1,4,5)IP3-sensitive pool. Furthermore, the rate of thapsigargin-induced release was significantly increased in the continued presence of an (1,4,5)IP3 stimulus. Thus, Ca2+ reuptake apparently occurred into the (1,4,5)IP3- and thapsigargin-sensitive Ca2+ store and (1,4,5)IP3 continued to influence the permeability of this pool to Ca2+ during Ca2+ reuptake. In contrast to the findings in permeabilized cells, Ca2+ reuptake did not occur in the sustained presence of (1,4,5)IP3 in intact parotid cells. We conclude that cell permeabilization reveals a kinetic, and presumably structural, separation of Ca2+ uptake and release sites within the (1,4,5)IP3-regulated intracellular organelle.
Menniti
F S
FS
Calcium Regulation Section, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709.
Bird
G S
GS
Takemura
H
H
Thastrup
O
O
Potter
B V
BV
Putney
J W
JW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D004163:Diphosphoglyceric Acids / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007700:Kinetics; D015388:Organelles / Q000378:metabolism; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D013997:Time Factors
D004163:Diphosphoglyceric Acids; D013729:Terpenes; C015891:glycerate 1,3-biphosphate; D004533:Egtazic Acid; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D002118:Calcium