THE EFFECTS OF ALTERING EXTRACELLULAR POTASSIUM-ION CONCENTRATION ON THE MEMBRANE-POTENTIAL AND CIRCADIAN CLOCK OF PARAMECIUM-BURSARIA

In some neural models of circadian rhythmicity, membrane potential and transmembrane flux of potassium and calcium ions appear to play impor tant roles in the entrainment and central mechanisms of the biological clock. We wondered whether these cellular variables might be generall y involved in circadian clocks, even non-neural clocks. Therefore, we tested the impact of changing extracellular potassium level on the cir cadian rhythm of photoaccumulation of Paramecium cells, whose membrane potential responds to changes of extracellular potassium in a manner similar to that of neurones. We found that pulse or step changes of ex tracellular potassium concentration did not phase-shift the circadian clock of P. bursaria cells in a phase-specific manner. Furthermore, mo difying the extracellular concentration of calcium did not affect the magnitude of light-induced phase resetting. Therefore, while membrane potential and calcium fluxes may be crucial components of the circadia n clock system in some organisms, especially in neural systems that in volve intercellular communication, the P. bursaria data indicate that membrane potential changes are not necessarily an intrinsic component of circadian organization at the cellular level.