CA2+ ENTRY MODULATES OSCILLATION FREQUENCY BY TRIGGERING CA2+ RELEASE

As in many cells, the frequency of agonist-induced cytosolic Ca2+ conc entration ([Ca2+](i)) oscillations in exocrine avian nasal gland cells is dependent on the rate of Ca2+ entry. Experiments reveal that the i nitiation of each oscillatory spike is independent of the relative ful lness of the stores and, furthermore, the oscillating pool is normally fully refilled by the end of each [Ca2+](i) spike. Therefore, contrar y to current models, the interspike interval (which essentially sets t he frequency) does not reflect the time taken to recharge the oscillat ing stores. Instead, the data show that it is the previously demonstra ted role that Ca2+ entry plays in triggering the repetitive release of Ca2+ from the oscillating stores, rather than the recharging of those stores, that provides the basis for the observed effects of Ca2+ entr y rate on oscillation frequency.