Inactivation of Octopamine in Larval Firefly Light Organs by a High-affinity Uptake Mechanism

1. Uptake studies using radioactive octopamine have revealed that the larval lantern of the Photuris firefly possesses a concentrative, high-affinity uptake system for octopamine. This compound has been shown previously to be the neurotransmitter of the photomotor neurones. 2. Imipramine is a potent inhibitor of the uptake of octopamine in the lantern. At 10~moll~', it reduces specific uptake of radioactive octopamine with a K, of 5-8xlO~moll~. Incubation of lanterns in 2-5xlO~moll~' imipramine induces an increase in sensitivity of the luminescent response to endogenously released and exogenously applied octopamine. Release of endogenous octopamine is potentiated in imipramine-treated lanterns, which also show a significant reduction of octopamine content with this treatment. 3. Uptake of octopamine does not appear to be affected by denervation of the lanterns, suggesting that nerve terminals are not the principal sites of octopamine uptake.