TY - JOUR T1 - Effects of adrenochrome on calcium accumulating and adenosine triphosphatase activities of the rat heart microsomes. JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 688 LP - 693 VL - 214 IS - 3 AU - S Takeo AU - G M Taam AU - R E Beamish AU - N S Dhalla Y1 - 1980/09/01 UR - http://jpet.aspetjournals.org/content/214/3/688.abstract N2 - The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-5.4 x 10(-4) M) on microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent adenosine triphosphatase (ATPase) activities was studied in vitro. Adrenochrome decreased microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The inhibitory effect of adrenochrome on microsomal calcium uptake activity of the isolated membrane was independent of pH (6.0-8.0), calcium concentrations (10-200 muM), protein concentration (0.02-0.10 mg/ml), temperature (25-37 degrees C) and incubation time (2-30 min). Kinetic study of calcium uptake activity in different concentrations of ATP showed that the inhibition was of a mixed type. Perfusion of hearts with adrenochrome resulted in marked depression in contractile force and the microsomal fraction obtained from these hearts showed depressed calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The depression in microsomal The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-an irreversible nature. It is proposed that cardiodepressant action of adrenochrome may partly be explained on the basis of its inhibitory effect on the calcium transporting ability of the sarcoplasmic reticulum. ER -