Contribution of mitochondria to the removal of intracellular Ca2+ induced by caffeine and rapid cooling at low temperatures in ferret ventricular muscles.
We investigated the role of mitochondria in the removal of intracellular Ca2+ which was increased by caffeine (15 mM, Caf), rapid lowering of the solution temperature from 30 to 4 degrees C (rapid cooling, RC), and electrical stimulation (0.07 Hz, ES). For this purpose, the intracellular Ca2+ concentration ([Ca2+]i) was measured using aequorin from the superficial cells of ferret papillary muscles. The three maneuvers induced transient changes in [Ca2+]i with different time courses. The decay time of the aequorin light signal (DT) in the Caf-induced Ca2+ release was significantly prolonged by the inhibitors for Na+-Ca2+ exchanger (Ni2+, Na+-free solution) at higher temperatures (> or = 12 degrees C). In the caffeine application at lower temperatures (< or = 12 degrees C), the inhibitors for mitochondria (ruthenium red, NaN3) significantly prolonged the DT but other inhibitors were ineffective. In the RC-induced Ca2+ release, DT was significantly prolonged by the mitochondrial inhibitors but other inhibitors were not effective. In the ES-induced Ca2+ release, each inhibitor for the sarcoplasmic reticulum (SR) (thapsigargin and 2,5-di(tert-butyl)-1,4-benzohydroquinone) prolonged the DT at all temperatures. The inhibitors for Na+-Ca2+ exchanger slightly prolonged the DT only at higher temperatures, and the mitochondrial inhibitors did not alter the DT at any temperature. These results suggest that mitochondria substantially transport Ca2+ when the Ca2+ uptake by the SR and Na+-Ca2+ exchanger are inhibited and [Ca2+]i is increased with a slower time course.
Tanaka
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E
Department of Physiology, The Jikei University School of Medicine, Tokyo, Japan.
Kurihara
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S
D000331:Aequorin; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D003080:Cold Temperature; D004558:Electric Stimulation; D005289:Ferrets; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism*; D013997:Time Factors
D002110:Caffeine; D000331:Aequorin; D002118:Calcium