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Synergistic activation of guinea‐pig cardiac cystic fibrosis transmembrane conductance regulator by the tyrosine kinase inhibitor genistein and cAMP
Author(s) -
Shuba Lesya M.,
McDonald Terence F.
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.023bc.x
Subject(s) - forskolin , genistein , cystic fibrosis transmembrane conductance regulator , chemistry , protein tyrosine phosphatase , phosphorylation , protein kinase a , endocrinology , medicine , tyrosine phosphorylation , tyrosine kinase , long term potentiation , protein kinase c , signal transduction , biology , biochemistry , stimulation , receptor , gene
1 The regulation of cardiac Cl − current ( I C1 ) by tyrosine and serine/threonine phosphorylation was examined in guinea‐pig and rat ventricular myocytes. The protein tyrosine kinase (PTK) inhibitor genistein (GST) and phosphotyrosine phosphatase (PTP) inhibitor sodium orthovanadate (VO 4 ) were used to modify tyrosine phosphorylation, whereas forskolin (FSK), cAMP, and other agents were used to modify cytoplasmic cAMP concentration and protein kinase A (PKA) phosphorylation. 2 Low concentrations (0.1 μ m ) of FSK did not activate the PKA‐regulated cystic fibrosis transmembrane regulator (CFTR) I Cl in guinea‐pig ventricular myocytes, but strongly potentiated activation of an I Cl by 20–100 μ m GST. The potentiation did not occur when GST was replaced by PTK‐inactive daidzein, and it was strongly inhibited by 1 m m VO 4 . 3 Potentiation by 0.1 μ m FSK was linked to a small stimulation of the adenylate cyclase–cAMP–PKA pathway. The potentiation was not mimicked by inactive 1,9‐dideoxyforskolin, and was inhibited by muscarinic stimulation (ACh) and by a PKA inhibitor. Internal application of a cAMP solution that alone was too weak to activate CFTR I Cl strongly potentiated the activation of I Cl by 50 μ m GST and occluded potentiation by 0.1 μ m FSK. 4 The foregoing suggests that potentiated I Cl flows through cAMP‐dependent CFTR channels. In agreement with this interpretation, GST did not increase I Cl when CFTR was maximally activated by a high concentration (5 μ m ) of FSK and okadaic acid, and neither GST nor GST plus FSK activated an I Cl in CFTR‐deficient rat myocytes. The lack of effect in rat myocytes was not due to the absence of functional, channel‐relevant PKA and PTK–PTP systems, because (as in guinea‐pig myocytes) L‐type Ca 2+ current ( I Ca,L ) was stimulated by FSK and inhibited in a VO 4 ‐reversible manner by GST. 5 The synergistic activation of CFTR by low concentrations of FSK and GST cannot be explained by either a GST‐induced elevation of cAMP concentration or inhibition of serine/threonine phosphatase. Rather, it appears to be due to tyrosine dephosphorylation that facilitates PKA‐mediated phosphorylation of the channels.