Decreased susceptibility of cultured smooth muscle cells from SHR rats to growth inhibition by heparin

Smooth muscle cell proliferation is regulated through the coordinated action of growth inhibitors and growth factors/mitogens; a specific heparin‐epidermal growth factor (EGF) complementation has been proposed (Reilly et al., 1987, J. Cell. Physiol., 131:149–157). In culture, vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) proliferate more rapidly than VSMC from control Wistar Kyoto rats (WKY). We observed that, compared with WKY‐derived VSMC, cells from SHR were markedly less susceptible to growth inhibition both by heparin and its homopolysaccharide analogue pentosan polysulphate (PPS). SHR‐derived VSMC exhibited a reduced capacity for binding of [3H]heparin to specific extracellular surface receptors, whereas affinities for heparin were comparable between both VSMC isolates. The early (0–2 hr at 37°C) kinetics of internalization did not differ between SHR‐ and WKY‐derived VSMC, but both internalized equivalent proportions (∼ 10%) of initially surface‐bound heparin. VSMC from SHR exhibited a greater capacity, without a changed affinity, for [I125]EGF binding than VSMC from WKY. Pre‐exposure of VSMC to heparin or PPS decreased, in a time‐dependent manner, the EGF binding capacity for both SHR and WKY (by 40–50% after 72 hr). However, in absolute terms, the EGF‐binding capacity of VSMC from SHR exposed to heparinoids was similar to that of nonexposed VSMC from WKY.