Homogeneous Ca2+ stores in rat adrenal chromaffin cells.
The localization and function of Ca(2+) stores in isolated chromaffin cells of rat adrenal medulla were investigated using confocal laser microscopy and amperometry. Binding sites for BODIPY-inositol 1,4,5-trisphosphate (IP(3)), -ryanodine (Ry), and -thapsigargin (Thap) were both perinuclear and at the cell periphery. The endoplasmic reticulum (ER), which was identified by ER Tracker dye, took up fluorescent Ry and IP(3), and the majority of BODIPY-Ry-binding area was bound by fluorescent IP(3). Under Ca(2+)-free conditions, the amount of caffeine-induced catecholamine secretion was 33% of that of muscarine-induced secretion, but muscarine induced little or no secretion after exposure to caffeine. Muscarine-induced Ca(2+) increases, as observed with fluo-3, lasted for a few tens of seconds under Ca(2+)-free conditions, whereas a caffeine-induced Ca(2+) transient diminished rapidly with a half decay time of 3s and this spike-like Ca(2+) transient was then followed by a sustained increase with a low level. These results indicate that IP(3) receptors and Ry receptors (RyRs) are present in common ER Ca(2+) storage and the lower potency of caffeine for secretion may be due to a rapid decrease in RyR channel activity to a low level.
Inoue
Masumi
M
Department of Physiology, Fukuoka University School of Medicine, Fukuoka 814-0180, Japan. minoue@fukuoka-u.ac.jp
Sakamoto
Yasuji
Y
Fujishiro
Naoji
N
Imanaga
Issei
I
Ozaki
Shoichiro
S
Prestwich
Glenn D
GD
Warashina
Akira
A
D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002395:Catecholamines / Q000378:metabolism; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009116:Muscarine / Q000494:pharmacology; D051381:Rats; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism
D015220:Calcium Channels; D002395:Catecholamines; D005456:Fluorescent Dyes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D009116:Muscarine; D002118:Calcium