Studies of adrenergic hormone action and protein thiolation in beating rat heart cells

Beating rat heart cell cultures were used to study the effects of (alpha)- and (beta)-adrenergic stimulation on contraction rate, cAMP, glycogen phosphorylase, glycogen synthase, and protein phosphorylation in the myocardial cell. Both (alpha)- and (beta)-adrenergic stimulation increased the beating rate of the heart cells. (alpha)-Adrenergic stimulation produced stable increases in the beating rate which were not depenent upon or modified by cellular cAMP increases. (beta)-Adrenergic stimulation of the beating rate was transient and dependent upon increases in cellular cAMP. The (beta)-adrenergic cAMP response was unchanged by simultaneous stimulation of the (alpha)-adrenergic receptor, but was desensitized by previous (beta)-stimulation of the heart cells. (beta)-Adrenergic desensitization was (beta)-receptor-specific and was not due to increases in cAMP in the heart cells. Epinephrine treatment of the heart cells produced activation of glycogen phosphorylase and inactivation of glycogen synthase. These responses were mediated exclusively by the (beta)-adrenergic receptor and resulted from increases in cellular cAMP. The effects of (alpha)- and (beta)-adrenergic stimulation on phosphorylation of glycogen phosphorylase in the heart cells was examined by isolating heart cell glycogen phosphorylase. These studies clearly showed that heart cell glycogen phosphorylase was phosphorylated only in response to (beta)-adrenergic stimulation. (beta)-Adrenergic stimulation increased the phosphorylation of seven other proteins with apparent subunit molecular weights of 236,000, 229,000, 161,000, 125,000, 102,000, 86,000, and 25,000. A 78,000 dalton protein was dephosphorylated in response to (beta)-adrenergic stimulation;The extent of protein thiolation in a soluble fraction of the heart cells was examined. (\u2735)S-cysteine was incorporated into reduction-sensitive bonds of heart cell proteins. The rate of labeling of protein was very similar to the rate of glutathione labeling. Cysteine and glutathione were identified as the only radioactive thiols released from the heart proteins by reduction. SDS-polyacrylamide electrophoresis showed that a large number of heart cell proteins were thiolated