Expression of Smooth Muscle Myosin Heavy Chain B in Cardiac Vessels of Normotensive and Hypertensive Rats

From Humboldt University (Charité), Department of Physiology, Berlin (I.M.), and Max Delbrück Center for Molecular Medicine, Berlin-Buch (U.W., G.L., H.H., U.G., I.M.), Germany.

Correspondence to Prof Ingo Morano, Max Delbrück Center for Molecular Medicine, Robert-Rössle-Straße 10, 13122 Berlin-Buch, Germany. E-mail imorano{at}orion.rz.mdc-berlin.de

Abstract—We investigated expression of the 5'-spliced isoform of smooth muscle myosin heavy chain (SM-MHC-B) in smooth muscle cells of cardiac vessels of the left ventricle of normotensive (Wistar-Kyoto) and spontaneously hypertensive rats of the stroke-prone strain by immunofluorescence microscopy. In parallel, liver and bladder were studied for characterization of the nature of vessels expressing SM-MHC-B and for semiquantitative evaluation of its abundance. Smooth muscle cells were detected by staining with a monoclonal antibody specific for -smooth muscle actin. Abundance of the SM-MHC-B isoform in these cells was evaluated by using an antibody raised against the seven–amino acid insert at the 25K/50K junction of the myosin head (a25K/50K) that specifically recognized SM-MHC-B. In the ventricle, a25K/50K immunoreactivity was observed in smooth muscle cells of precapillary arterioles but not in larger vessels or aorta. The a25K/50K immunoresponse of those vessels with the highest expression level of SM-MHC-B closely resembled the signal observed in the smooth muscle layer of urinary bladder known to preferentially express SM-MHC-B. Interestingly, in left ventricles of stroke-prone spontaneously hypertensive rats, there was a significantly reduced fraction of a25K/50K-positive precapillary arterioles compared with normotensive control rats.

Key Words: smooth muscle • myosin heavy chain • hypertrophy • hypertension • cardiac vessel

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