Intracellular injections of BAPTA block induction of enhancement in Hermissenda type B-photoreceptors.

Light paired with serotonin (5-HT) in vivo produces both short- and long-term enhancement of generator potentials in identified B-photoreceptors in Hermissenda. The role of intracellular Ca2+ in the induction of enhancement in B-photoreceptors was assessed by buffering intracellular Ca2+ with the iontophoretic injection of BAPTA. Blocking light-elicited photoreceptor desensitization with BAPTA loading prior to applying 5-HT was used as an indication of the effectiveness of Ca2+ buffering. Enhancement was blocked in preparations that received BAPTA loading prior to the application of 5-HT while typical enhancement was elicited by light and 5-HT in control preparations. These results indicate that enhancement involves a Ca(2+)-dependent process.