Sarcoplasmic reticulum Ca2+ depletion by caffeine and changes of [Ca2+](i) during refilling in bovine airway smooth muscle cells

• Published in: Archives of medical research Vol. 31; no. 6; pp. 558 - 563
• Main Authors: Bazán-Perkins, B, Sánchez-Guerrero, E, Carbajal, V, Barajas-López, C, Montaño, L M
• Format: Journal Article
• Language: English
• Published: United States 01.11.2000
• Subjects: Amiloride - analogs & derivatives; Amiloride - pharmacology; Animals; Caffeine - pharmacology; Calcium - metabolism; Calcium Channels - drug effects; Calcium Channels - physiology; Calcium Signaling - drug effects; Carbachol - pharmacology; Cattle; Cells, Cultured; Gallopamil - pharmacology; Indoles - pharmacology; Ion Transport - drug effects; Ionomycin - pharmacology; Ionophores - pharmacology; Muscle, Smooth - cytology; Muscle, Smooth - drug effects; Potassium Chloride - pharmacology; Sarcoplasmic Reticulum - drug effects; Sarcoplasmic Reticulum - metabolism; Sodium-Calcium Exchanger - drug effects; Sodium-Calcium Exchanger - physiology; Trachea - cytology
• ISSN: 0188-4409
• DOI: 10.1016/S0188-4409(00)00156-9

In airway smooth muscle (ASM), Ca2+ influx in response to the Ca2+ depletion of the sarcoplasmic reticulum (SR) seems to play a role in the regulation of intracellular free Ca2+ concentrations ([Ca2+](i)). This study evaluates some possible Ca2+ entry pathways activated during SR-Ca2+ depletion induced by 10 mM caffeine. Enzymatically dispersed bovine ASM cells were loaded with Fura-2/AM to permit measurement of [Ca2+](i) changes in single cells. Caffeine (10 mM) induced a transient increase in [[Ca2+](i) that depleted SR-Ca(2)+ content. After caffeine washout, a decrease in basal [Ca2+](i) (undershoot) was invariably observed, followed by a slow recovery. This phenomenon was inhibited by cyclopiazonic acid (5 microM). External Ca(2)+ removal in depolarized and nondepolarized cells induced a decrease in basal [Ca2+](i) that continued until depletion of the SR-Ca2+ content. The decrease in [Ca2+](i) induced by Ca2+-free physiological saline solution (PSS) was accelerated in caffeine-stimulated cells. Recovery from undershoot was not observed in Ca2+-free PSS. Depolarization with KCl and addition of D600 (30 microM) did not modify recovery. Similar results were obtained when the Na(+)/Ca2+ exchanger was blocked by substituting NaCl with KCl in normal PSS (Na(+)-free PSS) or by adding benzamil amiloride (25 microM). SR-Ca2+ content plays an important role in the Ca2+ leak induced by Ca2+-free medium, and does not depend on membrane potential. Additionally, recovery from undershoot after caffeine depends on extracellular Ca2+, and neither voltage-dependent Ca2+ channels nor the Na(+)/Ca2+ exchanger are involved.