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 exhibi t [Ca2+](i) oscillations, spontaneously or after moderate stimulation with treatments that induce polyphosphoinositide hydrolysis or mild de polarization. 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 demontrate that in cult ured chromaffin cells either one of these oscillation reinforcements c an be elicited, depending on whether the Ca2+ influx induced by the ap plied stimulus is asynchronous with or timed by the [Ca2+](i) spikes o f 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) mod els. (C) 1994 Academic Press, Inc.