Connexin expression in cultured neonatal rat myocytes reflects the pattern of the intact ventricle

Objective: Primary cultures of neonatal rat ventricular myocytes have become a widely used model to examine a variety of functional, physiological and biochemical cardiac properties. In the adult rat, connexin43 (Cx43) is the major gap junction protein present in the working myocardium. In situ hybridization studies on developing rats, however, showed that Cx40 mRNA displays a dynamic and heterogeneous pattern of expression in the ventricular myocardium around birth. The present studies were performed to examine the expression pattern of the Cx40 protein in neonatal rat heart, and to examine the connexins present in cultures of ventricular myocytes obtained from those hearts. Methods: Cryosections were made of hearts of 1-day-old Wistar rats. Cultures of ventricular myocytes obtained from these hearts by enzymatic dissociation were seeded at various densities (to obtain >75, ∼50%, and 75% confluency) Cx43 and Cx40 immunoreactivity could be detected. In contrast to Cx43 immunolabeling which showed a homogeneous distribution pattern, Cx40 staining was heterogeneous, i.e. in some clusters of cells abundant labeling was present whereas in others no Cx40 staining could be detected. The pattern of Cx43 immunoreactivity was not altered by the culture density. In contrast, in isolated ventricular myocytes cultured at low density (