Abstract
A mathematical model of calcium dynamics in vascular smooth muscle cell (SMC) was developed based on data mostly from rat mesenteric arterioles. The model focuses on (a) the plasma membrane electrophysiology; (b) Ca 2+ uptake and release from the sarcoplasmic reticulum (SR); (c) cytosolic balance of Ca 2+, Na +, K +, and Cl − ions; and (d) IP 3 and cGMP formation in response to norepinephrine (NE) and nitric oxide (NO) stimulation. Stimulation with NE induced membrane depolarization and an intracellular Ca 2+ ([Ca 2+] i) transient followed by a plateau. The plateau concentrations were mostly determined by the activation of voltage-operated Ca 2+ channels. NE causes a greater increase in [Ca 2+] i than stimulation with KCl to equivalent depolarization. Model simulations suggest that the effect of [Na +] i accumulation on the Na +/Ca 2+ exchanger (NCX) can potentially account for this difference. Elevation of [Ca 2+] i within a concentration window (150–300 nM) by NE or KCl initiated [Ca 2+] i oscillations with a concentration-dependent period. The oscillations were generated by the nonlinear dynamics of Ca 2+ release and refilling in the SR. NO repolarized the NE-stimulated SMC and restored low [Ca 2+] i mainly through its effect on Ca 2+-activated K + channels. Under certain conditions, Na +–K +-ATPase inhibition can result in the elevation of [Na +] i and the reversal of NCX, increasing resting cytosolic and SR Ca 2+ content, as well as reactivity to NE. Blockade of the NCX's reverse mode could eliminate these effects. We conclude that the integration of the selected cellular components yields a mathematical model that reproduces, satisfactorily, some of the established features of SMC physiology. Simulations suggest a potential role of intracellular Na + in modulating Ca 2+ dynamics and provide insights into the mechanisms of SMC constriction, relaxation, and the phenomenon of vasomotion. The model will provide the basis for the development of multi-cellular mathematical models that will investigate microcirculatory function in health and disease.
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