EXPRESSION OF SMOOTH-MUSCLE MYOSIN HEAVY-CHAIN-B IN CARDIAC VESSELS OF NORMOTENSIVE AND HYPERTENSIVE RATS

We investigated expression of the 5'-spliced isoform of smooth muscle myosin heavy chain (SM-MHC-B) in smooth muscle cells of cardiac vessel s of the left ventricle of normotensive (Wistar-Kyoto) and spontaneous ly hypertensive rats of the stroke-prone strain by immunofluorescence microscopy. In parallel, liver and bladder were studied for characteri zation of the nature of vessels expressing SM-MHC-B and for semiquanti tative evaluation of its abundance. Smooth muscle cells were detected by staining with a monoclonal antibody specific for alpha-smooth muscl e actin. Abundance of the SM-MHC-B isoform in these cells was evaluate d by using an antibody raised against the seven-amino acid insert at t he 25K/50K junction of the myosin head (a25K/50K) that specifically re cognized SM-MHC-B. In the ventricle, a25K/50K immunoreactivity was obs erved in smooth muscle cells of precapillary arterioles but not in lar ger vessels or aorta. The a25K/50K immunoresponse of those vessels wit h the highest expression level of SM-MHC-B closely resembled the signa l observed in the smooth muscle layer of urinary bladder known to pref erentially express SM-MHC-B. Interestingly, in left ventricles of stro ke-prone spontaneously hypertensive rats, there was a significantly re duced fraction of a25K/50K-positive precapillary arterioles compared w ith normotensive control rats.