Overexpression of the integrin $beta;1A subunit and the $beta;1A cytoplasmic domain modifies the $beta;-adrenergic regulation of the cardiac L-type Ca2+current

Abstract

<h2>Abstract</h2> Integrins are a family of cell-surface receptors that link the extracellular matrix (ECM) to the cellular cytoskeleton. The goal of this study was to determine the importance of the integrin β₁ subunit in regulating cardiac L-type Ca²⁺ channel function. Neonatal rat ventricular myocytes were cultured on collagen membranes and infected with adenovirus expressing either the human β_1A integrin (Adβ_1A) or a chimeric protein consisting of the cytoplasmic tail domain of the β_1A integrin and the extracellular/transmembrane domain of the interleukin-2 receptor (AdTAC-β₁). Expression of the free β₁ integrin tail (TAC-β₁), but not the full-length β_1A integrin, altered cell morphology and disrupted normal cell adhesion. When compared with myocytes infected with control virus, neither Adβ_1A nor AdTAC-β₁ infection produced any significant change in the current vs. voltage relationship of the whole-cell Ca²⁺ current (<i>I</i>_Ca) or the kinetics of <i>I</i>_Ca decay. Expression of TAC-β₁, but not β_1A, induced a negative shift in the Ca²⁺ channel steady-state inactivation curve. Application of the β-adrenergic receptor agonist isoproterenol produced over a 90% increase in <i>I</i>_Ca in control cells, but caused only an 18% increase in myocytes overexpressing the full-length β_1A integrin. In addition, β-adrenergic stimulation resulted in a 5–10-fold increase in intracellular cAMP levels in control cells, but produced no significant response in Adβ_1A-infected cells. In contrast, expression of TAC-β₁ was associated with an augmentation in the Ca²⁺ channel response to isoproterenol (160% increase) and the Ca²⁺ channel agonist BayK8644. Thus, integrin/ECM interactions may be critical in the regulation of <i>I</i>_Ca