A model of calcium regulation in smooth muscle cell

A model of smooth muscle cell is proposed to describe the mechanisms by which intracellular calcium (Ca_i) is regulated when the cell is stimulated by noradrenaline (NA)/agonist (Ag) or depolarized. The intracellular Ca²⁺ store is comprised of two calcium pools: A-store which is sensitive to inositol 1,4,5 trisphosphate (IP₃) and C-store, insensitive to IP₃ but sensitive to Ca_i. The A-store is refilled by Ca²⁺ from C-store and reuptake of Ca_i. The uptake rate is dependent on the degree of filling in the A-store. The C-store, activated by Ca_i, is replenished by extracellular Ca²⁺ (Ca₀). IP₃ generated by NA or Ag changes the A-store permeability, discharging its Ca²⁺ into the cytosol. Depolarization activates Ca²⁺ current through the L-type channels. The following events are simulated and compared with experimental observations: (a) Ca_i transient stimulated by high K⁺; (b) Ca_i transient and Ca²⁺ efflux induced by shortlasting and longlasting NA in the absence of Ca₀; (c) effect of lanthanum on NA-induced Ca_i and Ca²⁺ efflux; and (d) effects of nifedipine, ryanodine, BAY K 8644 and cyclopiazonic acid on Ca_i.