Specific atrial overexpression of G protein coupled human β1 adrenoceptors in transgenic mice

Objective: The aim was to develop a transgenic mouse model of atrial β1 adrenoceptor overexpression in order to create atrial alteration of the receptor transduction system. Methods: Transgenic founders were generated after microinjection of the transgene construct into the pronucleus of fertilised mouse eggs. Heterozygous progeny were screened for RNA expression of the human β1 adrenoceptor gene under the control of a 0.56 kb proximal promoter of the human atrial natriuretic factor. One line, out of the three obtained, was selected and further characterised for overexpression of the human β1 adrenoceptor. Polymerase chain reaction was employed to detect β1 adrenoceptor mRNA, and 125I-cyanopindolol (ICYP) binding assays were used to quantify receptors in heart membranes. A quantitative autoradiographic ICYP binding technique was also used to visualise atrial and ventricular β adrenoceptors in heart sections. Results: The human β1 adrenoceptor was overexpressed specifically in the atria of transgenic mice. The level of the β1 adrenoceptor was 5-10-fold higher in transgenic mice compared to basal murine β1 adrenoceptors in non-transgenic control mice. Left and right atrial receptor overexpression was confirmed by in vitro autoradiography. The human receptors were able to couple to the murine stimulatory G proteins (Gs), as shown by high affinity binding site dosage using the β adrenoceptor agonist isoprenaline. Isoprenaline displacement studies allowed the determination of two different affinity sites, one of high affinity (KH = 5.8 nM), and one of low affinity (KL = 520 nM). When expressed in terms of protein density (fmol·mg−1), atrial transgenic β1 adrenoceptors displayed a threefold increase in high affinity sites (KH) as compared to control mice. Preliminary electrocardiographic data showed supraventricular premature beats in 6/14 transgenic mice v 2/16 control mice. Conclusions: These transgenic mice may provide a useful pharmacological tool to investigate the pathophysiological consequences of the overactivation of atrial β1 adrenoceptor-adenylyl cyclase signalling system. Cardiovascular Research 1993; 27 :1606-1612