The relative relevance of phosphorylation of the Thr¹⁷ residue of phospholamban is different at different levels of β-adrenergic stimulation
Contractility and relaxation measurements were combined with the determination of total phospholamban (PLB) phosphorylation and the immunodetection of PLB-phosphorylation sites in the intact, beating rat heart to identify the contributions of PLB phosphorylation at the Thr¹⁷ and Ser¹⁶ residues at di...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2002 |
| País: | Argentina |
| Institución: | Universidad Nacional de La Plata |
| Repositorio: | SEDICI (UNLP) |
| Idioma: | español |
| OAI Identifier: | oai:sedici.unlp.edu.ar:10915/144219 |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/144219 |
| Access Level: | acceso abierto |
| Palabra clave: | Medicina Phospholamban phosphorylation sites β-Adrenoceptor stimulation Myocardial relaxation |
| Sumario: | Contractility and relaxation measurements were combined with the determination of total phospholamban (PLB) phosphorylation and the immunodetection of PLB-phosphorylation sites in the intact, beating rat heart to identify the contributions of PLB phosphorylation at the Thr¹⁷ and Ser¹⁶ residues at different levels of β-adrenoceptor stimulation. Whereas with 30-300 nM isoproterenol, phosphorylation of Thr¹⁷, the Ca²⁺-calmodulin-dependent protein kinase-II (CaMKII) site and Ser¹⁶, the protein kinase A (PKA) site, contributed approximately 50% each to PLB phosphorylation, and both participated in the relaxant action of isoproterenol, at lower a level of β-adrenoceptor stimulation (isoproterenol 0.3-3 nM), both effects were exclusively due to Ser¹⁶ phosphorylation. Increasing [Ca]<sub>o</sub> at 3 nM isoproterenol, to obtain an increase in contractility comparable to that produced by 30 nM isoproterenol, significantly increased Thr¹⁷ phosphorylation and the relaxant effect produced by 3 nM isoproterenol. An increase in Thr¹⁷ phosphorylation and in the relaxant effect of 3 nM isoproterenol was also obtained by phosphatase inhibition (okadaic acid). In this case, Ser¹⁶ phosphorylation was also increased. Moreover, perfusion with 30 nM isoproterenol in the presence of the PKA inhibitor H-89 decreased phosphorylation at both PLB residues and diminished the inotropic and relaxant responses to the β-agonist. The relative contribution of Thr¹⁷ phosphorylation to the isoproterenol-induced phosphorylation of PLB and relaxation thus increased with the level of β-adrenoceptor stimulation and the consequent increase in PKA activity. The lack of Thr¹⁷ phosphorylation at low isoproterenol concentrations might therefore be attributed to a level of PKA activity insufficient to increase [Ca]<sub>i</sub> to activate the CaMKII system and/or to inhibit the phosphatase that dephosphorylates PLB. |
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