The emerging role of Ca2+ sensitivity regulation in promoting myogenic vasoconstriction.
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.
Schubert
Rudolf
R
University of Rostock, Institute of Physiology, PSF 100888, D-18055 Rostock, Germany. rudolf.schubert@medizin.uni-rostock.de
Lidington
Darcy
D
Bolz
Steffen-Sebastian
SS
D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006801:Humans; D008564:Membrane Potentials; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D009218:Myosins / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D017382:Reactive Oxygen Species; D015398:Signal Transduction; D014661:Vasoconstriction; D020742:rhoA GTP-Binding Protein / Q000502:physiology
D000199:Actins; D024681:Potassium Channels, Calcium-Activated; D017382:Reactive Oxygen Species; D011493:Protein Kinase C; D009218:Myosins; D020742:rhoA GTP-Binding Protein; D002118:Calcium