Distribution of two distinct Ca2+-ATPase-like proteins and their relationships to the agonist-sensitive calcium store in adrenal chromaffin cells.
Many cellular functions are regulated by activation of cell-surface receptors that mobilize calcium from internal stores sensitive to inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). The nature of these internal calcium stores and their localization in cells is not clear and has been a subject of debate. It was originally suggested that the Ins(1,4,5)P3-sensitive store is the endoplasmic reticulum, but a new organelle, the calciosome, identified by its possession of the calcium-binding protein, calsequestrin, and a Ca2+-ATPase-like protein of relative molecular mass 100,000 (100K), has been described as a potential Ins(1,4,5)P3-sensitive calcium store. Direct evidence on whether the calciosome is the Ins(1,4,5)P3-sensitive store is lacking. Using monoclonal antibodies raised against the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum, we show that bovine adrenal chromaffin cells contain two Ca2+-ATPase-like proteins with distinct subcellular distributions. A 100K Ca2+-ATPase-like protein is diffusely distributed, whereas a 140K Ca2+-ATPase-like protein is restricted to a region in close proximity to the nucleus. In addition, Ins(1,4,5)P3-generating agonists result in a highly localized rise in cytosolic calcium concentration ([Ca2+]i) initiated in a region close to the nucleus, whereas caffeine results in a rise in [Ca2+]i throughout the cytoplasm. Our results indicate that chromaffin cells possess two calcium stores with distinct Ca2+-ATPases and that the organelle with the 100K Ca2+-ATPase is not the Ins(1,4,5)P3-sensitive store.
Burgoyne
R D
RD
Physiological Laboratory, University of Liverpool, UK.
Cheek
T R
TR
Morgan
A
A
O'Sullivan
A J
AJ
Moreton
R B
RB
Berridge
M J
MJ
Mata
A M
AM
Colyer
J
J
Lee
A G
AG
East
J M
JM
D000313:Adrenal Medulla / Q000187:drug effects / Q000201:enzymology*; D000803:Angiotensin I / Q000494:pharmacology*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D000911:Antibodies, Monoclonal; D001572:Benzofurans; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism*; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology*; D008970:Molecular Weight
D000911:Antibodies, Monoclonal; D001572:Benzofurans; D005456:Fluorescent Dyes; D007527:Isoenzymes; D008688:Methacholine Compounds; D016210:Methacholine Chloride; D000804:Angiotensin II; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D000803:Angiotensin I; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2