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 gamma-aminobutyric acid (GABA) type A (GABA(A)) 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)(-). Measured aCl(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 GABA(A) receptors. These results suggest that aCl(i)(-) participates in modulating GABA(A) receptor functions on SCN neurons during the circadian rhythm.