Oscillations of cytosolic calcium in rat chromaffin cells: Dual modulation in frequency and amplitude

Rat chromaffin cells in primary culture have a high tendency to exhibit [Ca²⁺](i) oscillations, spontaneously or alter moderate stimulation with treatments that induce polyphosphoinositide hydrolysis or mild depolarization. Previous studies in a variety of cell systems had shown that strengthening of the above treatments increases the frequency and not the amplitude of the oscillations. We now demonstrate that in cultured chromaffin cells either one of these oscillation reinforcements can be elicited, depending on whether the Ca²⁺ influx induced by the applied stimulus is asynchronous with or timed by the [Ca²⁺](i) spikes of the oscillations. In excitable cells the encoding of the oscillation activity appears therefore to operate according to not only digital (modulation in frequency) but also analog (modulation in amplitude) models.