Protein phosphatase activity is increased in a rat model of long-term beta-adrenergic stimulation.
We tested the hypothesis that altered phosphorylation of Ca2+ regulatory proteins contributes to contractile anomalies in cardiac hypertrophy. Cardiac hypertrophy was induced in rats by chronic s.c. administration of isoproterenol (Iso, 2.4 mg/kg/day) via osmotic minipumps. On day 2 of Iso treatment the expression of atrial natriuretic factor was increased, time of relaxation in isolated papillary muscles shortened and protein expression of phospholamban (PLB) and sarcoplasmic reticulum Ca2+-ATPase reduced. In addition, the phosphorylation state of PLB at serine-16 and threonine-17 was decreased from (arbitrary units) 2.3+/-0.3 to 1.1+/-0.2 and from 4.1+/-0.6 to 2.1+/-0.2, respectively. This was not accompanied by altered activity of PLB-phosphorylating protein kinases (protein kinase A or Ca2+/calmodulin-dependent protein kinase II), whereas the activity of types 1 and 2A protein phosphatases (PP1 and -2A respectively) was enhanced from 1.1+/-0.08 to 1.71+/-0.13 nmol/mg/min. Iso treatment did not alter the PP1/PP2A activity ratio and 1 nmol/l okadaic acid, a concentration which completely blocks the catalytic subunit of PP2A, inhibited about 40% of total PP activity in all groups studied. These data indicate that the activity of both PP1 and PP2A were increased. All effects of Iso treatment were abolished by co-administration of propranolol (29.7 mg/kg/day). It is concluded that dephosphorylation of PLB is due to enhanced activity of PP1 and PP2A. We suggest that chronic beta-adrenergic stimulation, which occurs in human cardiac hypertrophy and failure, can lead to increased activity of PPs. This may contribute to altered contractile responses in the hypertrophied heart.
Bokník
P
P
Institut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität Münster, Germany. boknik@uni-muenster.de
Fockenbrock
M
M
Herzig
S
S
Knapp
J
J
Linck
B
B
Lüss
H
H
Müller
F U
FU
Müller
T
T
Schmitz
W
W
Schröder
F
F
Neumann
J
J
D000318:Adrenergic beta-Agonists / Q000633:toxicity*; D000704:Analysis of Variance; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D006332:Cardiomegaly / Q000139:chemically induced / Q000201:enzymology / Q000378:metabolism*; D004195:Disease Models, Animal; D004347:Drug Interactions; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000633:toxicity; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011433:Propranolol / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099211:Phospholamban
D000318:Adrenergic beta-Agonists; D002135:Calcium-Binding Proteins; D004791:Enzyme Inhibitors; D007545:Isoproterenol; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D011433:Propranolol; D011494:Protein Kinases; D000099211:Phospholamban