Simple fluctuation of Ca2+ elicits the complex circadian dynamics of cyclic AMP and cyclic GMP in Paramecium.
The circadian dynamics of cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) were simulated in Paramecium multimicronucleatum. The mathematical functions determined closely mimic the Ca2+ dependence of adenylate cyclase (AC) and guanylate cyclase (GC) activities as documented in P. tetraurelia. Patterns of cAMP concentration ([cAMP]), cGMP concentration ([cGMP ]), and the ratio [cGMP]/[cAMP] were calculated with respect to Ca2+ concentrations ([Ca2+]) fluctuating sinusoidally with a period of 24 hours at three different levels: low, medium, and high. The functions displayed varying patterns of [cAMP] characteristic for [Ca2+] fluctuating at each level, while patterns of [cGMP] and [cGMP]/[cAMP] almost paralleled [Ca2+] fluctuations. Similar patterns were observed for actual [cAMP] and [cGMP] measured during the light/dark cycle in P. multimicronucleatum, grown in axenic media additionally containing [Ca2+] at 25 (low), 100 (medium), or 400 (high) microM, respectively. The coincidence between simulated and measured fluctuations of [cAMP] and [cGMP] suggests that the circadian fluctuations of intracellular [Ca2+] primarily stimulate activities of AC and GC via their different degrees of Ca2+ dependence, which are ultimately responsible for the circadian spatiotemporal organization of various physiological functions in Paramecium.
Hasegawa
K
K
Division of Brain Sciences, Graduate School of Medicine, Kitasato University, Sagamihara, Kanagawa 228-0829, Japan. khase@medcc. kitasato-u.ac.jp.
Kikuchi
H
H
Ishizaki
S
S
Tamura
A
A
Tsukahara
Y
Y
Nakaoka
Y
Y
Iwai
E
E
Sato
T
T
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002940:Circadian Rhythm / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D003624:Darkness; D006162:Guanylate Cyclase / Q000378:metabolism; D008027:Light; D008954:Models, Biological; D010247:Paramecium / Q000378:metabolism*
D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D002118:Calcium