Synchronization of Cellular Contractions in the Arteriolar Wall
With few exceptions all tissues in the mammalian body are invested by a highly branched microcirculatory network. The microcirculation serves to bring the blood into close contact with every part of the tissue. In this way the exchange between blood and t
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Synchronization of Cellular Contractions in the Arteriolar Wall Jens C.B. Jacobsen, Bjørn O. Hald, Jens C. Brasen, and Niels-Henrik Holstein-Rathlou
Smooth muscle cells can display different types of calcium dynamics, ranging from small localized events over waves of calcium release that propagate through the cell to global oscillations in which the calcium concentration in all regions of the cytoplasm oscillate in synchrony. The latter case typically also leads to synchronization with neighboring cells.
10.1 Introduction With few exceptions all tissues in the mammalian body are invested by a highly branched microcirculatory network. The microcirculation serves to bring the blood into close contact with every part of the tissue. In this way the exchange between blood and tissue of oxygen, nutrients, metabolic bi-products, etc. can be bridged efficiently by diffusion. Like most other hollow structures in the body, the wall of arterioles and small muscular arteries (resistance vessels) are invested with a specific kind of contractile cell known as the smooth muscle cell (SMC). The SMC is long and spindle shaped. Under the microscope its interior does not appear as highly organized as, for instance, the cells of skeletal muscle tissue. In the latter kind of cells the structure of the contractile machinery can be directly observed, but this is not the case for the SMC. In addition, contraction or relaxation of the SMC is involuntary, i.e. we cannot control it by will. For a number of reasons, however, the contractile characteristics of the SMC make it well suited to participate in the regulation of our internal milieu.
J.C.B. Jacobsen () B.O. Hald J.C. Brasen N.-H. Holstein-Rathlou Panum Institute, University of Copenhagen, Blegdamsvej 3B, DK-2200 Copenhagen, Denmark e-mail: [email protected]; [email protected]; [email protected]; [email protected] E. Mosekilde et al. (eds.), Biosimulation in Biomedical Research, Health Care and Drug Development, DOI 10.1007/978-3-7091-0418-7 10, © Springer-Verlag/Wien 2012
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First and most importantly, the SMC is capable of sustaining a certain level of contraction (normally denoted “tone”) of the vascular wall. The advantage of operating with a certain tone in the basal state is that the vessel diameter can be regulated both up and down. Hence, the flow through the lumen of the vessel can be regulated very efficiently. In this connection, it should be kept in mind that the laminar flow in a tube varies proportionally to the radius to the fourth power. A relatively modest change in diameter can thus have profound influence on the volume flow. Here it is important, of course, that the metabolic cost of sustaining a certain level of tone in SMC tissue is very low since the smooth muscle cells may enter a so-called “latch” state with low energy consumption despite a sustained contraction. Second, the vascular smooth muscle cells display an intrinsic reaction to changes in stress, following e.g. changes in luminal pressure. An increase in stre
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