MODULATION OF FUNCTION IN LIMULUS COMPOUND EYE PHOTORECEPTORS BY OCTOPAMINE ENANTIOMERS

Octopamine has been identified as a circadian neurotransmitter in Limu lus photoreceptor organs, which can increase photoreceptor response to light. Here we report that the naturally occurring D(-)-octopamine is much more effective in increasing the response to light in Limulus la teral eye photoreceptor cells in vitro than its L(+) enantiomer, which appears to act as an antagonist of D(-)-octopamine. The effect of bot h enantiomers on the response to light is slow to develop, and slow to disappear following their removal. Such behavior is appropriate for a system which produces a long-term, steady change of state in the phot oreceptor organs.