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Laminin acts via focal adhesion kinase/phosphatidylinositol‐3′ kinase/protein kinase B to down‐regulate β 1 ‐adrenergic receptor signalling in cat atrial myocytes
Author(s) -
Wang Y. G.,
Ji X.,
Pabbidi M.,
Samarel A. M.,
Lipsius S. L.
Publication year - 2009
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 - 10.1113/jphysiol.2008.163824
Subject(s) - myocyte , wortmannin , medicine , endocrinology , ly294002 , chemistry , laminin , stimulation , protein kinase b , kinase , phosphatidylinositol , biology , microbiology and biotechnology , signal transduction , extracellular matrix
We previously reported that short‐term (2 h) plating of cat atrial myocytes on the extracellular matrix protein, laminin (LMN) decreases adenylate cyclase activity and β 1 ‐adrenergic receptor (β 1 ‐AR) stimulation of L‐type Ca 2+ current ( I Ca,L ). The present study sought to determine whether LMN‐mediated down‐regulation of β 1 signalling is due to down‐regulation of adenylate cyclase and to gain insight into the signalling mechanisms responsible. β 1 ‐AR stimulation was achieved by 0.01 μ m isoproterenol (isoprenaline) plus 0.1 μ m ICI 118551, a selective β 2 ‐AR antagonist. Atrial myocytes were plated for at least 2 h on uncoated cover‐slips (−LMN) or cover‐slips coated with LMN (+LMN). As previously reported, β 1 ‐AR stimulation of I Ca,L was significantly smaller in +LMN compared to −LMN atrial myocytes. In −LMN myocytes, 10 μ m LY294002 (LY), a specific inhibitor of PI‐(3)K, had no effect on β 1 ‐AR stimulation of I Ca,L . In +LMN myocytes, however, LY significantly increased β 1 ‐AR stimulation of I Ca,L . Western blots revealed that compared with −LMN myocytes, +LMN myocytes showed a significant increase in Akt phosphorylation at Ser‐473, which was prevented by LY. In another approach, +LMN myocytes were infected (multiplicity of infection (MOI), 100; 24 h) with replication‐defective adenoviruses (Adv) expressing dominant‐negative inhibitors of focal adhesion kinase (FAK) (Adv‐FRNK or Adv‐Y397F‐FAK) or Akt (Adv‐dnAkt). Compared with control cells infected with Adv‐β‐galactosidase, cells infected with Adv‐FRNK, Adv‐Y397F‐FAK or Adv‐dnAkt each exhibited a significantly greater β 1 ‐AR stimulation of I Ca,L . In −LMN myocytes LY had no effect on forskolin (FSK)‐stimulated I Ca,L . However, in +LMN myocytes LY significantly increased FSK‐stimulated I Ca,L . Similar results were obtained in +LMN atrial myocytes infected with Adv‐FRNK. We conclude that LMN binding to β 1 ‐integrin receptors acts via FAK/PI‐(3)K/Akt to inhibit adenylate cyclase activity and thereby down‐regulates β 1 ‐AR‐mediated stimulation of I Ca,L . These findings provide new insight into the cellular mechanisms by which the extracellular matrix can modulate atrial β‐AR signalling.