Quantitative and qualitative heterogeneity in smooth muscle myosin heavy chains

Previous studies have shown that smooth muscle myosin consists of two heavy chains (MHCs) of unequal molecular weight; however, it is not clear whether there are intermuscle, inter- and intraspecies differences in the MHCs. The purpose of these experiments was to quantitatively and qualitatively compare MHCs in different smooth muscles. Extracts of bovine aorta (BAo), dog saphenous vein (dSV) and femoral artery (dFA), and rat aorta (rAo), femoral artery (rFA), carotid artery (rCA), ileum (rGI) and uterus (rUt) were electrophoresed on 5% polyacrylamide-1% SDS gels. All tissues exhibited two MHCs with molecular weights of 207,000 (MHC1) and 204,000 (MHC2) daltons. In all cases the proportion of total MHC made up by MHC1 was greater than that by MHC2. Based on their relative proportions (MHC1:MHC2), the tissues fell into one of three groups: (1) 55:45 - rAo, rCA, dFA; (2) 60:40 - dSV, BAo, rGI; and (3) 65:35 - rUt, rFA. Group 1 differed significantly from group 3 in the proportion of each MHC. One dimensional peptide maps indicated that BAo, dSV and dFA were similar while subtle differences existed between rUt and rAo. Differences between rUt and rAo were also observed in their cross-reactivity to a monoclonal antibody to smooth muscle MHC, confirming the differences seen on peptide maps. These results indicate that there are intertissue and inter- and intraspecies differences in smooth muscle MHCs. The significance of these differences to muscle function remains to be determined.