EFFECT OF COLLAGENASE ON SURFACE EXPRESSION OF IMMUNOREACTIVE FIBRONECTIN AND LAMININ IN FRESHLY ISOLATED CARDIAC MYOCYTES

The extracellular glycoproteins fibronectin (FN) and laminin (LMN) are ubiquitously expressed in myocardial tissue. These glycoproteins are important for cellular attachment and differentiation of the cardiac m yocytes. Utilizing specific antibodies for the detection of FN and LMN , respectively, the distribution of these extracellular proteins was e xamined in enzymatically isolated adult cardiac myocytes. Immunofluore scence staining of rod-shaped cardiac myocytes revealed only remnants of immunoreactive FN on the cellular surface and in the transverse tub ular membrane system. LMN expression, however, was preserved in a rast er-like pattern in the cardiac myocytes. In order to study the distrib ution of these glycoproteins at high resolution, scanning electron mic roscopy using the backscattered electron mode was combined with immuno gold staining and silver-enhancement. In addition, to confirm the immu nofluorescence microscopic observations it was shown that FN labelling was restricted to ill-defined extracellular material and that LMN was absent from the intercalated discs of the cardiac myocytes. The hyper contracted cells were characterized by numerous surface protrusions de void of immunoreactive LMN. Thus, these results indicate that FN and L MN are differently affected by collagenase treatment, and that these c hanges of glycoprotein expression may influence the normal function of the cardiac myocytes as well as the membrane stability during the dev elopment of irreversible cellular lesions. (C) 1998 Academic Press Lim ited.