A CLASS OF PARAMETRICALLY EXCITED CALCIUM OSCILLATION DETECTORS

Intracellular Ca2+ oscillations are often a response to external signa ls such as hormones. Changes in the external signal can alter the freq uency, amplitude, or form of the oscillations suggesting that informat ion is encoded in the pattern of Ca2+ oscillations. How might a cell d ecode this signal? We show that an excitable system whose kinetic para meters are modulated by the Ca2+ concentration can function as a Ca2oscillation detector. Such systems have the following properties: (1) They are more sensitive to an oscillatory than to a steady Ca2+ signal . (2) Their response is largely independent of the signal amplitude. ( 3) They can extract information from a noisy signal. (4) Unlike other frequency sensitive detectors, they have a flat frequency response. Th ese properties make a Ca2+-sensitive excitable system nearly ideal for detecting and decoding Ca2+ oscillations. We suggest that Ca2+ oscill ations, in concert with these detectors, can act as cellular timekeepe rs to coordinate related biochemical reactions and enhance their overa ll efficiency.