Mechanical control of cation channels in the myogenic response.

Microcirculatory vessel response to changes in pressure, known as the myogenic response, is a key component of a tissue's ability to regulate blood flow. Experimental studies have not clearly elucidated the mechanical signal in the vessel wall governing steady-state reduction in vessel diameter upon an increase in intraluminal pressure. In this study, a multiscale computational model is constructed from established models of vessel wall mechanics, vascular smooth muscle (VSM) force generation, and VSM Ca(2+) handling and electrophysiology to compare the plausibility of vessel wall stress or strain as an effective mechanical signal controlling steady-state vascular contraction in the myogenic response. It is shown that, at the scale of a resistance vessel, wall stress, and not stretch (strain), is the likely physiological signal controlling the steady-state myogenic response. The model is then used to test nine candidate VSM stress-controlled channel variants by fitting two separate sets of steady-state myogenic response data. The channel variants include nonselective cation (NSC), supplementary Ca(2+) and Na(+), L-type Ca(2+), and large conductance Ca(2+)-activated K(+) channels. The nine variants are tested in turn, and model fits suggest that stress control of Ca(2+) or Na(+) influx through NSC, supplementary Ca(2+) or Na(+), or L-type Ca(2+) channels is sufficient to produce observed steady-state diameter changes with pressure. However, simulations of steady-state VSM membrane potential, cytosolic Ca(2+), and Na(+) with pressure show only that Na(+) influx through NSC channel also generates known trends with increasing pressure, indicating that stress-controlled Na(+) influx through NSC is sufficient to generate the myogenic response.