Circadian rhythm in intracellular Cl− activity of acutely dissociated neurons of suprachiasmatic nucleus

A link between the circadian rhythm and the function of Cl−-permeable γ-aminobutyric acid (GABA) type A (GABAA) receptors on suprachiasmatic nucleus (SCN) neurons was studied by measuring intracellular activity of Cl−(aCl i − ) at different times during a circadian cycle in SCN neurons acutely dissociated from rat brains. To measure aCl i − , the voltage-clamp mode of the gramicidin-perforated patch-clamp technique was used, and reversal potential of GABA-induced currents (E GABA) was converted to aCl i − . MeasuredaCl i − was significantly higher at around noon (20.1 ± 1.4 mM) than at three other time zones of a circadian cycle (means ranging from 11.6 to 14.3 mM). Chord conductance of GABA-induced currents showed no circadian changes, indicating a lack of circadian changes in the number or single-channel conductance of GABAA receptors. These results suggest thataCl i − participates in modulating GABAA receptor functions on SCN neurons during the circadian rhythm.