Mechanism of the stimulation of calcium ion dependent ATPase of cardiac sarcoplasmic reticulum by adenosine 3',5'-monophosphate dependent protein kinase

Abstract

Canine cardiac sarcoplasmic reticulum (SR) is known to be phosphorylated by adenosine 3',5'-monophosphate (cAMP) dependent protein kinase on a 22 000-dalton protein. Phosphorylation enhances the initial rate of Ca2+ uptake and Ca2+-ATPase activity. To determine the molecular mechanism by which phosphorylation regulates the calcium pump in SR, we examined the effect of cAMP-dependent protein kinase on the individual steps of the Ca2+-ATPase reaction sequence. Cardiac sarcoplasmic reticulum was preincubated with cAMP and cAMP-dependent protein kinse in the presence (phosphorylated SR) and absence (control) of adenosine 5'-triphosphate (ATP). Control and phosphorylated SR were subsequently assayed for formation (4-200 ms) and decomposition (0-73 ms) of the acid-stable phosphorylated enzyme (E approximately P) of Ca2+-ATPase in media containing 100 microM [ATP] and various free [Ca2+]. cAMP-dependent phosphorylation of SR resulted in pronounced stimulation of initial rates and levels of E approximately P formed at low free [Ca2+] (less than or equal to 7 microM), but the effect was less at high free Ca2+ (greater than or equal to 10 microM). This stimulation was associated with a decrease in the dissociation constant for Ca2+ binding and a possible increase in Ca2+ sites. The observed rate constant for E approximately P formation of calcium-preincubated SR was not significantly altered by phosphorylation. Phosphorylation also increased the initial rate of E approximately P decomposition. These findings indicate that phosphorylation of cardiac SR by cAMP-dependent protein kinase regulates several steps in the Ca2+-ATPase reaction sequence which result in an overall stimulation of the calcium pump observed at steady state.

Phosphorylation and functional modifications of sarcoplasmic reticulum and myofibrils in isolated rabbit hearts stimulated with isoprenaline

“…(Tada et al, 1975), (2) the site of phosphorylation is a polymeric proteolipid named phospholamban (Lamers & Stinis, 1980;Kirchberger & Antonetz, 1982;Louis et al, 1982), and (3) the extent of phosphorylation. of phospholamban is directly correlated with the initial rate of Ca2+ transport by the SR vesicles LaRaia & Morkin, 1974) and the formation and decomposition of the phosphoenzyme (E -P) intermediate of the Ca2+-dependent ATPase (Kranias et al, 1980a;Tada et al, 1980). Experiments by several groups (LePeuch et al, 1980;Kranias & Solaro, 1982;Lindemann et al, 1983), have provided evidence consistent with an increase in phospholamban phosphorylation in SR preparations derived from hearts freeze-clamped during stimulation with catecholamines.…”

Tricyclohexyltin hydroxide effects on cationic and substrate activation kinetics of beta‐adrenergic–stimulated cardiac Ca2+‐ATPase

“…Evidence based on in vitro studies strongly suggests that betaadrenergic-mediated and CAMP-dependent phosphorylation of phospholamban is a mechanism for regulating Ca2+ transport by cardiac sarcoplasmic reticulum (9,(21)(22)(23)(24). In view of these reports, the effects of Plictran were also studied on beta-adrenergic-stimulated Ca2+-ATPase activity Qf cardiac sarcoplasmic reticulum.…”

Toxicity and the cardiovascular activity of organotin compounds: a review

“…[111] Phosphorylation of this protein results in stimulation of Ca 2+ -ATPase and Ca 2+ transport by the SR (Scheme 1). [110,112] Therefore, active calcium transport by cardiac SR has a key role in the excitation-contraction coupling of the myocardium, where Ca 2+ release from the SR induces contraction and re-accumulation of Ca 2+ by the SR leads to relaxation [108,110] (Scheme 1). If any compound alters SR calcium transport, it obviously affects the normal functioning of the heart.…”