title: Effects of ryanodine on a myocardial membrane vesicular fraction.
abstract: The effects of ryanodine on calcium transport were examined on a microsomal fraction isolated from guinea pig atrial muscle by sucrose density ultracentrifugation. The Ca+2 binding capacity of the fraction was sufficient to account for relaxation and was unaltered by the addition of 5x10(-5)M ryanodine. Exposure of the sarcoplasmic reticulum (SR) to concentrations of ryanodine which produce negative inotropy significantly reduced ATP-dependent calcium transport which was associated with a significant increase in the Ca+2 activated ATPase activity. The effect of ryanodine was to reduce the Ca/P ratio by 50%. These results suggest that the negative inotropic effect of ryanodine in guinea pig atrium is associated with the uncoupling of Ca+2 transport from ATP hydrolysis.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D006168:Guinea Pigs; D006325:Heart Atria; D066298:In Vitro Techniques; D008566:Membranes / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism
chemical_list: D000470:Alkaloids; D002132:Calcium Radioisotopes; D012433:Ryanodine; D000251:Adenosine Triphosphatases; D002118:Calcium