Ca2+ entry activated by emptying of intracellular Ca2+ stores in ileal smooth muscle of the rat.
1. The effects of depletion of intracellular Ca2+ stores on muscle tension and the intracellular Ca2+ concentration ([Ca2+])i were studied in fura-2 loaded longitudinal smooth muscle cells of the rat ileum. 2. After exposure to a Ca(2+)-free solution, application of Ca2+ caused a small contraction and a rise in [Ca2+]i, both of which were potentiated when the muscle was challenged with carbachol or caffeine before the addition of Ca2+. 3. Cyclopiazonic acid (CPA), a specific inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase, dose-dependently decreased tension development and the rises in [Ca2+]i induced by carbachol and caffeine in the Ca(2+)-free solution, but conversely increased the Ca(2+)-induced responses even in the presence of the voltage-dependent Ca2+ channel blockers, methoxyverapamil and nifedipine. 4. The contraction and rise in [Ca2+]i evoked by Ca2+ gradually declined with time after removal of CPA, while the reverse was the case for the responses to carbachol and caffeine. 5. The Ca(2+)-induced contraction and rise in [Ca2+]i in the presence of CPA were inhibited by the replacement of Na+ with K+ or Cs+, and by the addition of Cd2+, Ba2+, Ni2+ or La3+. 6. The influx of Mn2+ was much greater in extent in the presence of CPA than in its absence. 7. These results suggest that the emptying of intracellular Ca2+ stores may activate Ca2+ influx not associated with voltage-dependent Ca2+ channels in the rat ileal smooth muscle.
Ohta
T
T
Department of Pharmacology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
Kawai
K
K
Ito
S
S
Nakazato
Y
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D016257:Fura-2; D007082:Ileum / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008345:Manganese / Q000378:metabolism; D008670:Metals / Q000494:pharmacology; D009130:Muscle, Smooth / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D007211:Indoles; D008670:Metals; D008345:Manganese; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid