Activation of beta-adrenergic receptor kinase during myocardial ischemia.
During myocardial ischemia, a local release of noradrenaline coincides with an increased density of beta-adrenergic receptors. The functional activity of these receptors, however, is mainly determined by their state of phosphorylation. The beta-adrenergic receptor kinase (beta ARK) specifically phosphorylates and thereby inactivates beta-adrenergic receptors after stimulation by receptor agonists, facilitating the binding of the inhibitor protein beta-arrestin to the receptors. beta ARK activation involves a translocation of the enzyme to the membrane. In the present study, we investigated the density and the functional activity of beta-adrenergic receptors, the enzymatic activity of beta ARK in membranes and cytosol, the mRNA levels of beta ARK-1, and the expression of beta-arrestin during stop-flow and low-flow ischemia in the isolated perfused rat heart. After 60 minutes of stop-flow ischemia, beta-adrenergic receptor density was upregulated, but beta-agonist-mediated adenylate cyclase activity was blunted. Simultaneously, beta ARK activity in the particulate fraction was significantly induced. The increase in beta ARK activity was reversible after inhibition of ischemia-evoked noradrenaline release by desipramine. Also, exposure to externally given noradrenaline increased beta ARK activity in the particulate fraction. Cytosolic beta ARK activity remained largely unchanged during stop-flow or low-flow ischemia. The steady state concentration of beta ARK-1 mRNA increased after 20 minutes of stop-flow ischemia and then returned to baseline values after another 20 minutes. Cardiac ischemia did not alter beta-arrestin levels. During myocardial ischemia, an increase in the number of beta-adrenergic receptors is paralleled by increased membrane activity of the receptor kinase beta ARK. This increased membrane activity may contribute to enhanced receptor phosphorylation and inactivation.
Ungerer
M
M
1. Medizinische Klinik, Technischen Universität München, Germany. ungerer@med1.med.tu-muenchen.de
Kessebohm
K
K
Kronsbein
K
K
Lohse
M J
MJ
Richardt
G
G
D000818:Animals; D019390:Arrestins; D001483:Base Sequence; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D015335:Molecular Probes; D008969:Molecular Sequence Data; D017202:Myocardial Ischemia / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D051552:beta-Adrenergic Receptor Kinases; D000071557:beta-Arrestins
D019390:Arrestins; D005136:Eye Proteins; D015335:Molecular Probes; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D000071557:beta-Arrestins; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases