Calcium homeostasis in digitonin-permeabilized bovine chromaffin cells.
The regulation of cytosolic calcium was studied in digitonin-permeabilized chromaffin cells. Accumulation of 45Ca2+ by permeabilized cells was measured at various Ca2+ concentrations in the incubation solutions. In the absence of ATP, there was a small (10-15% of total uptake) but significant increase in accumulation of Ca2+ into both the vesicular and nonvesicular pools. In the presence of ATP, the permeabilized cells accumulated Ca2+ into carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-sensitive and -insensitive pools. The CCCP-sensitive pool--mainly mitochondria--was active when the calcium concentration was greater than 1 microM and was not saturated at 25 microM. The Ca2+ sequestered by the CCCP-insensitive pool could be inhibited by vanadate and released by inositol trisphosphate, a combination suggesting that this pool was the endoplasmic reticulum. The CCCP-insensitive pool had a high affinity for calcium, with an EC50 of approximately 1 microM. When the Ca2+ concentration was adjusted to the level in the cytoplasm of resting cells (0.1 microM), the presumed endoplasmic reticulum pool was responsible for approximately 90% of the ATP-stimulated calcium uptake. At a calcium level similar to the acetylcholine-stimulated level in intact cells (5-10 microM), most of the Ca2+ (greater than 95%) went into the CCCP-sensitive pool.
D000109:Acetylcholine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000311:Adrenal Glands / Q000378:metabolism*; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D002838:Chromaffin System / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology; D007700:Kinetics; D014638:Vanadates / Q000494:pharmacology
D002132:Calcium Radioisotopes; D005971:Glutamates; D007295:Inositol Phosphates; D000001:Calcimycin; D018698:Glutamic Acid; D014638:Vanadates; D004533:Egtazic Acid; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D004072:Digitonin; D000109:Acetylcholine; D002118:Calcium