The emerging role of Ca2+ sensitivity regulation in promoting myogenic vasoconstriction
1 University of Rostock, Institute of Physiology, PSF 100888, D-18055 Rostock, Germany
2 University of Toronto, Department of Physiology and Heart and Stroke/Richard Lewar Centre of Excellence in Cardiovascular Research, Medical Sciences Building, Rm 3326, 1 King's College Circle, Toronto, Canada ON M5S 1A8
* Corresponding author. Tel: +49 381 4948016; fax: +49 381 4948002.E-mail address: rudolf.schubert{at}medizin.uni-rostock.de (R. Schubert).
Growing evidence suggests that mechanisms which regulate the Ca2+ sensitivity of the contractile apparatus in vascular smooth muscle cells form the backbone of pressure-induced myogenic vasoconstriction. The modulation of Ca2+ sensitivity is suited to partially uncouple intracellular Ca2+ from constriction, thereby allowing the maintenance of tone with fully conserved function of other Ca2+-dependent processes. Following a brief review of ‘classical’ Ca2+-dependent signalling pathways involved in the myogenic response, the present review describes the emerging mechanisms that promote myogenic vasoconstriction via modulation of Ca2+ sensitivity. For the purpose of this review, Ca2+ sensitivity reflects the dynamic equilibrium between myosin light-chain kinase and myosin light-chain phosphatase activities in terms of its impact on vascular tone. Several signalling pathways (PKC, RhoA/Rho kinase, ROS) which have been identified as prominent regulators of Ca2+ sensitivity will be discussed. Although Ca2+ sensitivity modulation is clearly an important component of the myogenic response, attempts to integrate it into existing mechanistic models resulted in a two-phase model, with a predominant Ca2+-dependent ‘initiation/trigger’ phase followed by a Ca2+-independent ‘maintenance’ phase. We propose that the two-phase model is rather simplistic, because the literature reviewed here demonstrates that Ca2+-dependent and -independent mechanisms do not operate in isolation and are important at all stages of the response. The regulation of Ca2+ sensitivity, as an equal and complimentary partner of Ca2+-dependent processes, significantly enhances our understanding of the complex array of signalling pathways, which ultimately mediate the myogenic response.
KEYWORDS Myogenic response; Small arteries; Calcium sensitivity
Time for primary review: 21 days
This article was published online by Elsevier on 3 August, 2007.
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