title: Laminin enhances beta(2)-adrenergic receptor stimulation of L-type Ca(2+) current via cytosolic phospholipase A(2) signalling in cat atrial myocytes.
abstract: We previously reported that attachment of atrial myocytes to the extracellular matrix protein laminin (LMN), decreases adenylate cyclase (AC)/cAMP and increases beta(2)-adrenergic receptor (AR) stimulation of L-type Ca(2+) current (I(Ca,L)). This study therefore sought to determine whether LMN enhances beta(2)-AR signalling via a cAMP-independent mechanism, i.e. cytosolic phospholipase A(2) (cPLA(2)) signalling. Studies were performed on acutely isolated atrial myocytes plated on uncoated coverslips (LMN) or coverslips coated with LMN (+LMN). As previously reported, 0.1 microm zinterol (zint-beta(2)-AR) stimulation of I(Ca,L) was larger in +LMN than LMN myocytes. In +LMN myocytes, zint-beta(2)-AR stimulation of I(Ca,L) was inhibited by inhibition of cPLA(2) by arachidonyltrifluoromethyl ketone (AACOCF(3); 10 microm), inhibition of G(i) by pertussis toxin and chelation of intracellular Ca(2+) by 10 microm BAPTA-AM. In contrast to zinterol, stimulation of I(Ca,L) by fenoterol (fen-beta(2)-AR), a beta(2)-AR agonist that acts exclusively via G(s) signalling, was smaller in +LMN than LMN myocytes. Arachidonic acid (AA; 5 microm) stimulated I(Ca,L) to a similar extent in LMN and +LMN myocytes. Inhibition of cAMP-dependent protein kinase A (cAMP/PKA) by either 5 mum H89 or 1 microm KT5720 in LMN myocytes mimicked the effects of +LMN myocytes to enhance zint-beta(2)-AR stimulation of I(Ca,L), which was blocked by 10 microm AACOCF(3). In contrast, H89 inhibited fen-beta(2)-AR stimulation of I(Ca,L), which was unchanged by AACOCF(3). Inhibition of ERK1/2 by 1 microm U0126 inhibited zint-beta(2)-AR stimulation of I(Ca,L) in +LMN myocytes and LMN myocytes in which cAMP/PKA was inhibited by KT5720. In LMN myocytes, cytochalasin D prevented inhibition of cAMP/PKA from enhancing zint-beta(2)-AR stimulation of I(Ca,L). We conclude that LMN enhances zint-beta(2)-AR stimulation of I(Ca,L) via G(i)/ERK1/2/cPLA(2)/AA signalling which is activated by concomitant inhibition of cAMP/PKA signalling and dependent on the actin cytoskeleton. These findings provide new insight into the cellular mechanisms by which the extracellular matrix can remodel beta(2)-AR signalling in atrial muscle.
authors.affiliation: Loyola University Chicago, Stritch School of Medicine, Maywood, IL 60153, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Pabbidi
authors.forename: X
authors.initials: X
authors.lastname: Ji
authors.forename: A M
authors.initials: AM
authors.lastname: Samarel
authors.forename: S L
authors.initials: SL
authors.lastname: Lipsius
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002415:Cats; D002448:Cell Adhesion; D000242:Cyclic AMP / Q000378:metabolism; D004983:Ethanolamines / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006333:Heart Failure / Q000378:metabolism; D006801:Humans; D007797:Laminin / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D054510:Phospholipases A2, Cytosolic / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D000318:Adrenergic beta-Agonists; D020746:Calcium Channels, L-Type; D004983:Ethanolamines; D007797:Laminin; D018343:Receptors, Adrenergic, beta-2; C002904:zinterol; D000242:Cyclic AMP; D048049:Extracellular Signal-Regulated MAP Kinases; D054510:Phospholipases A2, Cytosolic
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