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+ (Ca(o)). 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 Ca(o); (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).