Phase-shifts of the Bulla ocular circadian pacemaker in the presence of calmodulin antagonists.

Previous work has shown that light-induced phase shifts of the Bulla ocular circadian pacemaker require extracellular calcium, suggesting the possibility that the action of calcium as a second messenger via calmodulin is an element in the phase shifting mechanism. The calmodulin antagonists calmidazolium, trifluoperazine (TFP) and W7 were applied with phase shifting light pulses. Light phase shifts were not blocked by calmidazolium or TFP, suggesting that calmodulin does not mediate light-induced phase shifts. Period changes were observed with treatments of both TFP and W7, but not with calmidazolium and are probably not calmodulin-mediated.