Effects of caffeine on calcium release and uptake by fragmented sarcoplasmic reticulum of frog skeletal muscle

Koshita, M.

Nagoya Medical Journal 31(3-4): 175-186


ISSN/ISBN: 0027-7649
Accession: 005293330

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The effects of caffeine on the Ca2+ release and uptake by sarcoplasmic reticulum (SR) isolated from frog skeletal muscle were studied by Ca2+ tracer method. SR (0.2 mg protein/ml) was loaded with 45CaCl2 (0.05 mM) in a solution containing ATP-regenerating system. SR took up about 120 and 200 nmol Ca2+/mg protein at steady state in the presence and absence of EGTA (0.2 mM), respectively. Ten mM but not 1 mM caffeine reduced the steady Ca2+ level in the presence of 0.2 mM EGTA, while it decreased only the rate of Ca2+ uptake in the absence of EGTA. Caffeine itself induced Ca2+ release from Ca2+ loaded SR even at a pCa of about 7, and the released Ca2+ induced further release of Ca2+ when free Ca2+ concentration was not buffered. Although Ca2+ released by caffeine was almost completely taken up, this was not the case when Ca2+ was released by 10 mM caffeine at a pCa of about 7. This incomplete reuptake may be the cause of caffeine contracture in intact muscle fibers.