Phase shifting of the circadian rhythm in the eye of Bulla by inhibition of chloride conductance.

Inhibition of Cl- conductance has been previously found to shorten the free-running period of the circadian eye rhythm of the marine snail Bulla gouldiana. In this study, we describe a phase-response curve for 6-h pulses of Cl(-)-free seawater, consisting only of phase advances with the largest in the late subjective night (1.5 h) and smaller phase shifts in the late subjective day. Intracellular recordings revealed that at both circadian times retinal pacemaker neurons hyperpolarized in response to the removal of extracellular chloride. Since previous studies indicate that membrane potential generates both phase advances and delays it seems unlikely that the action of chloride removal is mediated exclusively by the change in membrane potential.