Coordinated regulation of free Ca2+ by isolated organelles from a rat insulinoma.
Experiments aimed at the partial reconstitution of the intracellular transport systems regulating the cytosolic free Ca2+ homeostasis are reported. Rat insulinoma subcellular fractions enriched in mitochondria, endoplasmic reticulum (microsomes), and secretory granules were studied. The ambient free Ca2+ concentration maintained by the separate or combined organelles was determined with a Ca2+-selective minielectrode. The data demonstrate that ambient [Ca2+] is established by the microsomes, not by the mitochondria or the secretory granules, in the range of resting cytosolic Ca2+ concentrations (0.1-0.2 microM Ca2+). Furthermore, the microsomes are able to deplete largely the mitochondria of their exchangeable calcium. Nonetheless, both mitochondria and microsomes, but not secretory granules, function as a coordinated unit to restore the previous ambient [Ca2+] following its perturbation. Thus, mitochondria play a major role in bringing down rapidly ambient [Ca2+] to the submicromolar range, whereas the endoplasmic reticulum acts as a relay in the transport mechanisms which lower [Ca2+] to the resting level.
D007516:Adenoma, Islet Cell / Q000648:ultrastructure*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism / Q000648:ultrastructure*; D008861:Microsomes / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats
D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium