ISSN:
1573-4919
Keywords:
cardiomyocytes
;
protein phosphorylation
;
cAMP
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract In intact guinea pig ventricles, acetylcholine (ACH) has been shown to attenuate the positive inotropic effects of isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor, by reducing protein phosphorylation without altering cAMP levels. In the present study, we tested the hypothesis that the cAMP-independent inhibitory action of ACH is also evident in isolated cardiomyocytes. cAMP-dependent protein kinase (PKA) activity ratio (-cAMP/+cAMP) and phosphorylation of phospholamban (PLB) were determined in unlabeled and 32P-labeled guinea pig ventricular cardiomyocytes, respectively. IBMX increased PKA activity ratio and phosphorylation of PLB in a dose-dependent manner. When cardiomyocytes were incubated simultaneously with IBMX (0-1 mM) and ACH (2 μM), ACH attenuated PLB phosphorylation stimulated by low concentration (10-100 μM) but not by high concentrations (〉 200 μM) of IBMX. EC50 value for IBMX-induced phosphorylation of PLB was 32 ± 6 μM and increased nearly 3-fold after addition of ACH while PKA activity ratio remained unchanged. The rank order of cyclic nucleotide derivatives to phosphorylate PLB was 8 bromo-cAMP 〉 dibutyryl cAMP 〉 8 bromo-cGMP 〉 dibutyryl cGMP. ACH reduced phosphorylation of PLB stimulated by 8 bromo-cAMP. We conclude that in isolated cardiomyocytes (1) ACH inhibits phosphorylation of PLB stimulated by either IBMX or 8 bromo-cAMP and (2) ACH does not lower IBMX-stimulated PKA activity ratio. These effects of ACH on PLB phosphorylation cannot be explained by a reduction in IBMX-stimulated cAMP levels but may involve the activation of protein phosphatases.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1006899931151
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