Bioenergetics and the biochemical control of ciliary beating
Suphatra Adulrattananuwat, Jureepan Saranak and Kenneth Foster
Physics Department, Syracuse University, Syracuse, NY 13244-1130 USA
Most studies of ciliary beating report that the electrical signals generated by activation of rhodopsin photoreceptors control the beating. However, there are also chemical control signals from the cell body to the cilia. These can be elicited by stimulating the cell with 670 nm light which activates receptors in the chloroplast. We have monitored the ciliary responses of Chlamydomonas reinhardtii to the red light stimulus yielding information on the signal processing of this chemical control and the bioenergetics of the cilia. 806, a negative phototaxis strain, wild-type with respect to ciliary beating, and cpc1, a strain missing in the cilium the glycolytic pathway from 3-phosphoglycerate (3PG) to pyruvate, have been studied. Normally the beating frequency of cpc-1 cilia is only about ~60% of wild type, but with adequate ATP its cilia beats at the same frequency. The 3PG transported to the cilium makes additional ATP in the cilium as fuel for the dyneins. Step and sinusoidal (0.006 to 100 Hz) stimulation has been used. The responses to sine waves of both strains are full-wave rectified. The 806 beating frequency response can be written as a sin2(2*pi*freq.*time), while the cpc1 responses are negative transients. Therefore, the response shape must be determined within the cilia. The cpc1 has a shorter delay to response (0.37 ± 0.02 s) compare to that of the 806 (1.18s ± 0.02 s). It seems likely the extra 800 ms delay is used to synthesize the ATP from the 3PG. Unlike with green light stimulation the responses of each cilium are the same. The stroke velocity response is also marked but is quite independent from that of the beating frequency so that the signals that control them must also be different.
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