title: The effects of quinine on the calcium and magnesium content of the sarcoplasmic reticulum and the temperature-dependence of quinine contractures.
abstract: A significant decrease in the Ca2+ and increase in the Mg2+ content of the terminal cisternae (TC) of the sarcoplasmic reticulum (SR) during quinine contraction was demonstrated by electron probe analysis of rapidly frozen frog muscles. The extent of Ca2+ release (71% of total) from the TC and the absence of an increase in total cell Ca2+ support the conclusion that quinine contractures are caused by passive efflux of Ca2+ from the SR when the latter is uncompensated due to inhibition of the SR Ca2+ pump by quinine. A rapid warming contraction (RWC) was observed, in the presence of quinine, when the temperature of intact and skinned muscles was increased from about 5 degrees C to 18-23 degrees C. The duration of the latency of quinine contracture, in intact muscle bundles, was approximately 31 s at 3 degrees C and 2 s at 23 degrees C. The results suggest a significant temperature sensitivity of the passive Ca2+ channels of the SR membrane, although an effect of temperature on the lipid partition coefficient of quinine into the SR has not been ruled out.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003286:Contracture / Q000503:physiopathology*; D004577:Electron Probe Microanalysis; D007473:Ion Channels / Q000502:physiology; D008274:Magnesium / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000187:drug effects; D010710:Phosphates / Q000378:metabolism; D011803:Quinine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature
chemical_list: D007473:Ion Channels; D010710:Phosphates; D011803:Quinine; D008274:Magnesium; D002118:Calcium