Overexpression of the Integrin Beta(1A) Subunit and the Beta(1A) Cytoplasmic Domain Modifies the Beta-adrenergic Regulation of the Cardiac L-type Ca(2+)current

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 beta(1) subunit in regulating cardiac L-type Ca(2+) channel function. Neonatal rat ventricular myocytes were cultured on collagen membranes and infected with adenovirus expressing either the human beta(1A) integrin (Adbeta(1A)) or a chimeric protein consisting of the cytoplasmic tail domain of the beta(1A) integrin and the extracellular/transmembrane domain of the interleukin-2 receptor (AdTAC-beta(1)). Expression of the free beta(1) integrin tail (TAC-beta(1)), but not the full-length beta(1A) integrin, altered cell morphology and disrupted normal cell adhesion. When compared with myocytes infected with control virus, neither Adbeta(1A) nor AdTAC-beta(1) infection produced any significant change in the current vs. voltage relationship of the whole-cell Ca(2+) current (I(Ca)) or the kinetics of I(Ca) decay. Expression of TAC-beta(1), but not beta(1A), induced a negative shift in the Ca(2+) channel steady-state inactivation curve. Application of the beta-adrenergic receptor agonist isoproterenol produced over a 90% increase in I(Ca) in control cells, but caused only an 18% increase in myocytes overexpressing the full-length beta(1A) integrin. In addition, beta-adrenergic stimulation resulted in a 5-10-fold increase in intracellular cAMP levels in control cells, but produced no significant response in Adbeta(1A)-infected cells. In contrast, expression of TAC-beta(1) was associated with an augmentation in the Ca(2+) channel response to isoproterenol (160% increase) and the Ca(2+) channel agonist BayK8644. Thus, integrin/ECM interactions may be critical in the regulation of I(Ca)