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      Preferential Myosin Heavy Chain Isoform B Expression May Contribute to the Faster Velocity of Contraction in Veins versus Arteries

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          Smooth muscle myosin heavy chains occur in 2 isoforms, SMA (slow) and SMB (fast). We hypothesized that the SMB isoform is predominant in the faster-contracting rat vena cava compared to thoracic aorta. We compared the time to half maximal contraction in response to a maximal concentration of endothelin-1 (ET-1; 100 n M), potassium chloride (KCl; 100 m M) and norepinephrine (NE; 10 µ M). The time to half maximal contraction was shorter in the vena cava compared to aorta (aorta: ET-1 = 235.8 ± 13.8 s, KCl = 140.0 ± 33.3 s, NE = 19.8 ± 2.7 s; vena cava: ET-1 = 121.8 ± 15.6 s, KCl = 49.5 ± 6.7 s, NE = 9.0 ± 3.3 s). Reverse-transcription polymerase chain reaction supported the greater expression of SMB in the vena cava compared to aorta. SMB was expressed to a greater extent than SMA in the vessel wall of the vena cava. Western analysis determined that expression of SMB, relative to total smooth muscle myosin heavy chains, was 12.5 ± 4.9-fold higher in the vena cava compared to aorta, while SMA was 4.9 ± 1.2-fold higher in the aorta than vena cava. Thus, the SMB isoform is the predominant form expressed in rat veins, providing one possible mechanism for the faster response of veins to vasoconstrictors.

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          Most cited references 14

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          Myosins: a diverse superfamily

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              Regulation of force in vascular smooth muscle.

               O Ogut (2003)
              Vascular smooth muscle contraction plays a defining role in the regulation and maintenance of blood pressure, and its deregulation is associated with many clinical syndromes including hypertension, coronary vasospasm and congestive heart failure. Over the past 20 years, there has been a growing understanding of the regulation of 20 kDa myosin light chain phosphorylation by myosin light chain kinase and myosin light chain phosphatase, the role of splice-variant isoforms of both the myosin heavy chain and the essential myosin light chain, as well as the signaling pathways involved in smooth muscle contraction under normal and pathophysiological conditions. This review will attempt to recapitulate the data in the field, primarily focusing on the contractile response of smooth muscle, and the molecular determinants responsible for the regulation of vascular tone.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                June 2007
                21 March 2007
                : 44
                : 4
                : 264-272
                Departments of aPharmacology and Toxicology and bMedicine, Michigan State University, East Lansing, Mich., cDepartment of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vt., and dDepartment of Biological Sciences, Marquette University, Milwaukee, Wisc., USA
                100991 J Vasc Res 2007;44:264–272
                © 2007 S. Karger AG, Basel

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                Page count
                Figures: 5, References: 33, Pages: 9
                Research Paper


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