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      Phorbol Ester-Induced Contractions of Swine Carotid Artery Are Supported by Slowly Cycling Crossbridges Which Are Not Dependent on Calcium or Myosin Light Chain Phosphorylation

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          This study determined if phorbol ester-induced contraction of vascular smooth muscle requires calcium-dependent myosin light chain (MLC) phosphorylation and, if not, whether the mechanical characteristics of the contraction in terms of stiffness and crossbridge cycling are similar to those during a calcium- and MLC phosphorylation-dependent contraction. Carotid arterial strips were exposed to 1.0 µ M phorbol 12, 13-dibutyrate (PDBu) in the presence of normal physiological salt solution (PSS) or after calcium depletion in calcium-free PSS and compared with contraction elicited by calcium-containing 110 m M KCl-PSS. PDBu induced maximal stress in both the presence and absence of calcium. While there was a temporal correlation between MLC phosphorylation and shortening velocity during KC1 depolarization, shortening velocity was dissociated from MLC phosphorylation during PDBu stimulation. The stress-stiffness relationship was not different during KC1 and PDBu stimulation, suggesting similar crossbridge interactions even though MLC phosphorylation levels were significantly different. These results demonstrate that PDBu-induced contraction of the swine carotid artery is not dependent on calcium or MLC phosphorylation. We suggest the possibility that activation of a calcium-independent PKC isoform may result in the expression of an inherent level of actin-activated myosin ATPase activity resulting in the slow development of stress.

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          Author and article information

          J Vasc Res
          Journal of Vascular Research
          S. Karger AG
          23 September 2008
          : 30
          : 6
          : 315-322
          aBockus Research Institute, and bDepartment of Surgery, Graduate Hospital, Philadelphia, Pa., and cWeis Center for Research, Geisinger Clinic, Danville, Pa., USA
          159012 J Vasc Res 1993;30:315–322
          © 1993 S. Karger AG, Basel

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          Pages: 8
          Research Paper


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