Biochemical and electrophysiological mechanisms of the positive inotropic effect of calyculin A, a protein phosphatase inhibitor.
Calyculin A (CyA; 1 microM) increased the force of contraction in isolated guinea pig papillary muscles to 144% of control without affecting contraction parameters. The effect of CyA on L-type calcium channels was assessed in cell-attached patches of guinea pig ventricular cardiomyocytes. Unitary Ba++ current recordings revealed that CyA at micromolar concentrations enhanced channel availability almost 2-fold, whereas the duration of individual openings and closures remained unchanged. In whole-cell recordings with Ca++ as the charge carrier, intracellular dialysis of 1 microM CyA enhanced peak current to a similar extent. In homogenates from guinea pig ventricles, 1 microM CyA completely inhibited phosphorylase phosphatase activity. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, 1 microM CyA increased the phosphorylation state of phospholamban (to 267% of control), that of the inhibitory subunit of troponin (to 182% of control) and those of various additional proteins. We conclude that the effects of CyA are likely to be mediated by increasing the phosphorylation state of several regulatory proteins.
Neumann
J
J
Abteilung Allgemeine Pharmakologie, Universitäts-Krankenhaus Eppendorf, Hamburg, Germany.
Bokník
P
P
Herzig
S
S
Schmitz
W
W
Scholz
H
H
Wiechen
K
K
Zimmermann
N
N
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000378:metabolism; D004988:Ethers, Cyclic / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008387:Marine Toxins; D009200:Myocardial Contraction / Q000187:drug effects*; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D013268:Stimulation, Chemical; D000099211:Phospholamban
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D004988:Ethers, Cyclic; D008387:Marine Toxins; D019319:Okadaic Acid; D010080:Oxazoles; D010749:Phosphoprotein Phosphatases; D000099211:Phospholamban; C059041:calyculin A