Ca2+ entry modulates oscillation frequency by triggering Ca2+ release.

As in many cells, the frequency of agonist-induced cytosolic Ca2+ concentration ([Ca2+]1) oscillations in exocrine avian nasal gland cells is dependent on the rate of Ca2+ entry. Experiments reveal that the initiation of each oscillatory spike is independent of the relative fullness of the stores and, furthermore, the oscillating pool is normally fully refilled by the end of each [Ca2+]1 spike. Therefore, contrary to current models, the interspike interval (which essentially sets the frequency) does not reflect the time taken to recharge the oscillating stores. Instead, the data show that it is the previously demonstrated 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+ entry rate on oscillation frequency.