Vol. 283, Issue 6, H2322-H2330, December 2002
ACh and adenosine activate PI3-kinase in rabbit hearts
through transactivation of receptor tyrosine kinases
Thomas
Krieg1,
Qining
Qin1,
Elizabeth C.
McIntosh1,
Michael V.
Cohen1,2, and
James M.
Downey1
1 Departments of Physiology and
2 Medicine, University of South Alabama, Mobile, Alabama
36688
Adenosine and
acetylcholine (ACh) trigger preconditioning through different signaling
pathways. We tested whether either could activate myocardial
phosphatidylinositol 3-kinase (PI3-kinase), a putative signaling
protein in ischemic preconditioning. We used phosphorylation of
Akt, a downstream target of PI3-kinase, as a reporter. Exposure of
isolated rabbit hearts to ACh increased Akt phosphorylation 2.62 ± 0.33 fold (P = 0.001), whereas adenosine caused a
significantly smaller increase (1.52 ± 0.08 fold). ACh-induced activation of Akt was abolished by the tyrosine kinase blocker genistein indicating at least one tyrosine kinase between the muscarinic receptor and Akt. ACh-induced Akt activation was blocked by
the Src tyrosine kinase inhibitor
4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) and by 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG-1478), an
epidermal growth factor receptor (EGFR) inhibitor, suggesting phosphorylation of a receptor tyrosine kinase in an Src tyrosine kinase-dependent manner. ACh caused tyrosine phosphorylation of the
EGFR, which could be blocked by PP2, thus supporting this receptor
hypothesis. AG-1478 failed to block the cardioprotection of
ACh, however, suggesting that other receptor tyrosine kinases might be
involved. Therefore, Gi protein-coupled receptors can activate PI3-kinase/Akt through transactivation of receptor tyrosine kinases in an Src tyrosine kinase-dependent manner.
Akt; epidermal growth factor receptor; Src tyrosine kinase; acetylcholine; phosphatidylinositol 3-kinase