THE PARAMECIUM CIRCADIAN CLOCK - SYNCHRONY OF CHANGES IN MOTILITY, MEMBRANE-POTENTIAL, CYCLIC-AMP AND CYCLIC-GMP

The behavior of a ciliate protozoan, Paramecium, is known to represent the electrical state of the cell membrane, and regulation of the memb rane potential and ciliary motion are known to involve cAMP and cGMP. The present study shows the synchrony of circadian changes in motility , resting membrane potential and cyclic nucleotides in P. multimicronu cleatum. Using an automated system for tracking isolated single microo rganisms, the isolated Paramecium cells are confirmed to swim fast and straight during the day (and subjective day) and slowly, with frequen t turning, at night (and subjective night). The resting membrane poten tial is more negative during the day than at night. cAMP and cGMP conc entrations oscillate in a manner, such that both cAMP and cGMP are hig her during the day (or subjective day) than at night (or subjective ni ght). The ratio of cGMP to cAMP during the light and dark cycle (LD) f luctuates, paralleling the fluctuation of the resting membrane potenti al measured during the LD. These results suggest that the Paramecium w ill provide an excellent model to explore daily and circadian orchestr ation of second messengers mediating signals from ambient light/dark c ycles and circadian pacemaker to ion channels and cilia, directly invo lved in daily and circadian cellular outputs of resting membrane poten tial and motility.