Ca2+ currents and acid secretion in the isolated parietal cell involved in response to gastrin, compound 48/80, and ethylenediamine tetraacetic acid.
In intact guinea pig parietal cells, gastrin or compound 48/80 caused an initial increase in cytosolic Ca2+ concentration and subsequent acid secretion, owing to release of intracellulary stored Ca2+ besides the Ca2+ entry from the extracellular space. However, the maximum gastrin-induced Ca2+ entry into the cell was delayed by 60 min, a time which coincided with sustained acid secretion (by gastrin) that was dependent on medium Ca2+. On the other hand, there are two ATP-dependent Ca2+-removal systems detected in either plasmalemma or smooth surfaced membrane besides that of mitochondria. The plasmalemmal Ca2+-removal system was dependent on calmodulin. Smooth surfaced membrane vesicles caused an ATP-dependent Ca2+ uptake that was almost similar to that taken by saponin-permiabilized cell. In this system (permeable cell), myo-inositol 1,4,5-triphosphate (InsP3) caused the release of ATP-accumulated Ca2+ into the cytosol, suggesting an ATP-dependent and InsP3-sensitive Ca2+ pool(s) is in or near the smooth surfaced membranes. The ATP-dependent Ca2+ uptake by vesicles was markedly enhanced by the stimulation of cells with gastrin, compound 48/80, or EDTA. The increase of this Ca2+ uptake in stimulated cells by plasmalemmal vesicles exceeded that by smooth surfaced ones. The increase of the Ca2+ uptake by plasmalemmal vesicles was abolished by the cease of intracellular Ca2+ release without Ca2+ entry. In addition, gastrin or compound 48/80 evoked an early Ca2+ efflux across the plasma membrane owing to a pump that was independent of medium Ca2+ in intact cells. These results suggest that in the first acid secretion by gastrin or others, the Ca2+ released, which may be derived from an ATP-dependent and InsP3-sensitive Ca2+ pool, is mainly pumped out by the plasmalemmal Ca2+-removal system rather than the intracellular Ca2+-removal system; whereas the sustained acid secretion by gastrin required medium Ca2+ and in this phase, Ca2+ efflux across the plasma membrane became lower, suggesting that an ATP-dependent Ca2+ pool may be replenished by Ca2+ entering from the extracellular space.
D000632:Aminopyrine / Q000378:metabolism; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology*; D005744:Gastric Acid / Q000378:metabolism*; D005750:Gastric Juice / Q000187:drug effects*; D005753:Gastric Mucosa / Q000166:cytology* / Q000187:drug effects; D005755:Gastrins / Q000494:pharmacology*; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology*
D005755:Gastrins; D000632:Aminopyrine; D000001:Calcimycin; D003189:p-Methoxy-N-methylphenethylamine; D006632:Histamine; D002217:Carbachol; D004492:Edetic Acid; D002118:Calcium