Calcium dynamics in bovine adrenal medulla chromaffin cell secretory granules.
The secretory granules constitute one of the less well-known compartments in terms of Ca2+ dynamics. They contain large amounts of total Ca2+, but the free intragranular [Ca2+] ([Ca2+]SG), the mechanisms for Ca2+ uptake and release from the granules and their physiological significance regarding exocytosis are still matters of debate. We used in the present work an aequorin chimera targeted to the granules to investigate [Ca2+]SG homeostasis in bovine adrenal chromaffin cells. We found that most of the intracellular aequorin chimera is present in a compartment with 50-100 microM Ca2+. Ca2+ accumulation into this compartment takes place mainly through an ATP-dependent mechanism, namely, a thapsigargin-sensitive Ca2+-ATPase. In addition, fast Ca2+ release was observed in permeabilized cells after addition of inositol 1,4,5-trisphosphate (InsP3) or caffeine, suggesting the presence of InsP3 and ryanodine receptors in the vesicular membrane. Stimulation of intact cells with the InsP3-producing agonist histamine or with caffeine also induced Ca2+ release from the vesicles, whereas acetylcholine or high-[K+] depolarization induced biphasic changes in vesicular[Ca2+], suggesting heterogeneous responses of different vesicle populations, some of them releasing and some taking up Ca2+during stimulation. In conclusion, our data show that chromaffin cell secretory granules have the machinery required for rapid uptake and release of Ca2+, and this strongly supports the hypothesis that granular Ca2+ may contribute to its own secretion.
Santodomingo
Jaime
J
Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid and Consejo Superior de Investigaciones Científicas (CSIC), Ramón y Cajal, 7, E-47005 Valladolid, Spain.
Vay
Laura
L
Camacho
Marcial
M
Hernández-Sanmiguel
Esther
E
Fonteriz
Rosalba I
RI
Lobatón
Carmen D
CD
Montero
Mayte
M
Moreno
Alfredo
A
Alvarez
Javier
J
D000255:Adenosine Triphosphate / Q000378:metabolism; D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D000331:Aequorin / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002451:Cell Compartmentation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D002395:Catecholamines; D004791:Enzyme Inhibitors; D011993:Recombinant Fusion Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D000331:Aequorin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium