Effect of temperature on [3H]ryanodine binding to sarcoplasmic reticulum from bullfrog skeletal muscle.
It has been clarified that ryanodine binds to Ca2(+)-induced Ca release channels in the open state in sarcoplasmic reticulum. While the pharmacological action of ryanodine is known to be retarded at a low temperature, the Ca-releasing action of caffeine is potentiated at a low temperature. In order to obtain deeper insight into the molecular mechanism underlying Ca-release, the effect of temperature on ryanodine binding to the heavy fraction of sarcoplasmic reticulum (HFSR) from bullfrog skeletal muscle was examined. Although Ca2+ is indispensable for ryanodine binding, Ca2+ alone cannot cause ryanodine binding in a reaction medium of a salt concentration similar to that of the sarcoplasm. In addition to Ca2+, caffeine and/or beta,gamma-methylene adenosine triphosphate (AMPOPCP) are necessary. [3H]Ryanodine binding at 25 degrees C closely paralleled the Ca release activity in respect of the Ca2(+)-dependence in the presence of caffeine and/or AMPOPCP, and the effects of inhibitors. A Scatchard plot for ryanodine binding gave a straight linear line, indicating a single class of homogeneous binding sites. At 0 degrees C, the rate of ryanodine binding decreased. Q10 being about 3 on average. The affinity for ryanodine was reduced to about half that at 25 degrees C, with no change in the maximum number of binding sites. The temperature-dependent change in apparent affinity for Ca2+ on ryanodine binding is not always consistent with that in the case of Ca-release activity. The bound ryanodine may be in an occluded state because it did not dissociate for up to 90 h at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
Ogawa
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Y
Department of Pharmacology, Juntendo University School of Medicine, Tokyo.
Harafuji
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H
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000470:Alkaloids / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D011892:Rana catesbeiana; D012433:Ryanodine / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013696:Temperature
D000470:Alkaloids; D012433:Ryanodine; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D002110:Caffeine; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium