β₂-Adrenoceptor transfection enhances contractile reserve of isolated rat ventricular myocytes exposed to chronic isoprenaline stimulation by improving β₁-adrenoceptor responsiveness

Abstract

Context: Heart failure (HF) is a progressive deterioration in heart function associated with overactivity of the sympathetic nervous system. Elevated sympathetic nervous system activity down regulates the β-adrenergic signal system, suppressing β-adrenoceptors (β-ARs)-mediated contractile support in the failing heart.

Objective: We investigated the effects of β₂-AR gene transfer on shortening amplitude of isolated ventricular myocytes under chronic exposure to isoprenaline (ISO), and further determine the contributions of β₁-AR and β₂-AR to the contraction.

Materials and methods: Cardiomyocytes were isolated from adult rat hearts and then transfected with β₂-AR gene using an adenovirus vector. Four hours after the infection, cardiomyocytes were treated with ISO for another 24 hours to imitate high levels of circulating catecholamines in HF. Western blotting was performed to measure myocardial protein expression of β₂-AR. Video-based edge-detection system was used to evaluate basal and ISO-stimulated shortening amplitudes of cardiomyocytes.

Results: β₂-AR gene transfer increased β₂-AR protein content. Chronic ISO stimulation produced a negative inotropic response, whereas acute ISO stimulation showed a positive inotropic response. β₂-AR gene transfer had no significant effects on shortening amplitude of cardiomyocytes under normal conditions, but enhanced the blunted contraction of cardiomyocytes under pathological conditions induced by chronic ISO stimulation, and the effect was inhibited by β₁-AR antagonist, CGP 20712A, instead of β₂-AR antagonist, ICI 118,551.

Discussion and conclusions: We conclude that β₂-AR gene transfer in isolated ventricular myocytes under chronic ISO stimulation improves cellular contraction, and the beneficial effects might be mediated by improving β₁-adrenoceptor responsiveness.

Keywords::

• Gene therapy
• contraction
• heart failure

Acknowledgement

This study was supported by the Social Development Programme of Xuzhou (grant no. M08C063). We gratefully acknowledge the excellent technical assistance of Youjian Qi.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.