ONE-POOL MODEL FOR CA2-TRISPHOSPHATE AS CO-AGONISTS FOR CA2+ RELEASE(OSCILLATIONS INVOLVING CA2+ AND INOSITOL 1,4,5)

Experimental observations indicate that Ca2+-induced Ca2+ release (CIC R) may underlie Ca2+ oscillations in a variety of cells. In its origin al version, a theoretical model for signal-induced Ca2+ oscillations b ased on CICR assumed the existence of two types of pools, one sensitiv e to inositol 1,4,5-trisphosphate (IP3) and the other one sensitive to Ca Recent experiments indicate that Ca2+ channels may sometimes be se nsitive to both IP3 and Ca2+. Such a regulation may be viewed as Ca2+- sensitized IP3-induced Ca2+ release or, alternatively, as a form of IP 3-sensitized CICR. We show that sustained oscillations can still occur in a one-pool model, provided that the same Ca2+ channels are sensiti ve to both Ca2+ and IP3 behaving as co-agonists. This model and the tw o-pool model based on CICR both account for a number of experimental o bservations but differ in some respects. Thus, while in the two-pool m odel the latency and period of Ca2+ oscillations are of the same order of magnitude and correlate in a roughly linear manner, latency in the one-pool model is always brief and remains much shorter than the peri od of oscillations. Moreover, the first Ca2+ spike is much larger than the following ones in the one-pool model. These distinctive propertie s might provide an explanation for the differences in Ca2+ oscillation s observed in various cell types.