Intracellular Ca2+ shift and signal transduction from the tubulovesicular portion of gastric parietal cells during gastrin stimulation or Ca2+ ionophore treatment: comparison between luminescent and fluorescent probes, and electron probe X-ray microanalyzer.
In gastrin-stimulated, aequorin-loaded parietal cells from guinea pig gastric mucosa, a rapid but transient increase in the cytosolic free Ca2+ concentration ([Ca2+]i), owing to Ca2+ released from the store(s), and a more prolonged Ca2+ entry from outside the cells were observed. However, there was a little increase in [Ca2+]i when similar measurements were assessed by quin 2 or fura-2 in physiological saline. However, depletion or elimination of Na+ from the incubation medium caused a significant increase in the [Ca2+]; response to gastrin as measured by quin 2. These findings suggest that aequorin and quin 2 (or fura-2) provide information about different aspects of Ca2+ homeostasis and that there is an inhomogeneity of [Ca2+]i in the cytoplasm during gastrin stimulation. By the gastrin stimulation, the intracellular Ca2+ gradients were shifted from the unidentified portion(s) to the restricted apical cytoplasm, as determined by electron probe X-ray microanalysis. Therefore, localization and identification of the source of intracellular Ca2+ as a pool were determined by an X-ray microanalyzer. In the resting state, the tubulovesicle had high Ca2+ concentration compared with the level in the apical cytoplasm. Cells treated with the Ca2+ ionophore ionomycin had a decreased tubulovesicular Ca2+ level, followed by a reciprocal increase in area of the canalicular membrane. The secretory canaliculus in stimulated cells had lower Ca2+ or higher K+ and Cl- concentrations than that of tubulovesicles or cytoplasm in the resting state, respectively. These findings suggest that the Ca2+ pool of the parietal cell is in the tubulovesicles and (or) luminal cell membrane and that the Ca2+ released from the store(s) may mediate a flow of K+ or Cl- into the secretory canaliculus.
Tsunoda
Y
Y
Department of Laboratory Medicine, Hokkaido University School of Medicine, Japan.
Takeda
H
H
Otaki
T
T
Asaka
M
M
Nakagaki
I
I
Sasaki
S
S
D000331:Aequorin; D000634:Aminoquinolines; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002469:Cell Separation; D004577:Electron Probe Microanalysis; D005456:Fluorescent Dyes; D016257:Fura-2; D005755:Gastrins / Q000494:pharmacology*; D006168:Guinea Pigs; D007476:Ionophores / Q000494:pharmacology*; D010295:Parietal Cells, Gastric / Q000187:drug effects / Q000378:metabolism*
D000634:Aminoquinolines; D001572:Benzofurans; D005456:Fluorescent Dyes; D005755:Gastrins; D007476:Ionophores; D000331:Aequorin; C035739:Quin2; D002118:Calcium; D016257:Fura-2