Circadian rhythm of extracellular pH in crayfish at different levels of oxygenation.
The extracellular pH regulation was studied in the crayfish Astacus leptodactylus (a night animal) as a function of circadian rhythm. The venous acid-base balance (ABB) was determined in the morning (10 a.m.-12 a.m.) and in the evening (10 p.m.-12 p.m.) at PO2 ranging from 29 to 6 kPa and constant ABB in the water at 13 degrees C. In the morning the venous pH (pHv) was maintained constant by metabolic means independently of PO2 from 29 to 10 kPa. In the evening pHv again was constant and independent of PO2 but it was more alkaline by 0.1 unit corresponding to a shift along the in vitro buffer line. At that time, the ventilation required for providing a unit quantity of O2 (i.e. the ventilatory requirement) increased more than for simply providing O2. The related circadian changes of sensitivity of the ventilatory control system were assessed by comparing morning and evening ventilatory responses to 1-h periods of hypoxia and then hypercapnia. In the evening, the amplitude of the responses to both O2 and CO2 increased but the increase in CO2 sensitivity was proportionally more important. This is consistent with the increase of ventilatory requirement and the related decrease of hemolymph PCO2 during this period. It is concluded that in this animal there exists a circadian rhythm of extracellular pH that is achieved by controlling the CO2 partial pressure in the hemolymph. Results are discussed in terms of O2 transport processes and metabolic modulation through pH adjustments.
Sakakibara
Y
Y
Laboratoire d'Etude des Régulations Physiologiques, associé à l'Université Louis Pasteur, Centre National de la Recherche Scientifique, Strasbourg, France.
Burtin
B
B
Massabuau
J C
JC
D000136:Acid-Base Equilibrium; D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D002940:Circadian Rhythm; D005110:Extracellular Space / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D008297:Male; D010101:Oxygen Consumption