Chloride conductance contributes to period determination of a neuronal circadian pacemaker.

The isolated eye of Bulla gouldiana, a marine mollusc, is a circadian pacemaker. Previous studies have shown that membrane potential changes of neurons at the base of the Bulla retina play a critical role in the expression of the circadian rhythm and that the free-running period can be modified by chronic alteration of the resting membrane potential. We now report that treatments which inhibit CI- conductance shorten the free-running period. Substitution of CI- with the anions SO4(2-), isethionate and glutamate significantly shorten the period of the ocular rhythm in vitro. Furthermore, addition of the CI- channel blocker 9-anthracene-carboxylic acid (9-AC) is also effective at shortening the period of the circadian rhythm. These data suggest that a CI- conductance participates in determining the free-running period of the circadian pacemaker cells. This is the first report of CI- conductance involvement in a circadian system and the effect is remarkable in that few treatments are known which reliably shorten the period of circadian clocks.