Abstract
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.
| Original language | English |
|---|---|
| Journal | Journal of Biological Chemistry |
| Volume | 266 |
| Issue number | 21 |
| Pages (from-to) | 13646-53 |
| Number of pages | 8 |
| ISSN | 0021-9258 |
| Publication status | Published - 1991 |
| Externally published | Yes |
Keywords
- Animals
- Calcium
- Cell Compartmentation
- Cell Membrane Permeability
- Cells, Cultured
- Diphosphoglyceric Acids
- Egtazic Acid
- Heparin
- Inositol 1,4,5-Trisphosphate
- Kinetics
- Organelles
- Parotid Gland
- Rats
- Terpenes
- Thapsigargin
- Time Factors