Photic Stimulation of Intracellular cAMP-Dependent Protein Kinase in Paramecium

The cellular concentration of Paramecium protein kinase A (PKA) exhibits a bi-modal pattern in a 12-h light and 12-h dark cycle, with peaks around midday and immediately after dusk, in contrast to that measured in constant darkness (DD) which exhibits a mono-phasic pattern with a trough after subjective midday and a peak around subjective midnight. The bi-modal increases in PKA concentration caused by the onset (dawn) and offset (dusk) of illumination might contribute discrete phase-advances of the motility rhythm in P. multimicronucleatum. Fluctuation of PKA concentrations in DD is significantly related to that of frequency of changing moving-direction, on which PKA concentrations elevated during illumination may be additively observed to cause the bi-modal pattern.