Local anesthetics-induced inhibition of chloroplast electron transport

The effects of local anesthetics on photosynthetic activity of pea chloroplasts were investigated in order to elucidate the role of Ca2+ in photosynthetic electron transport. Dibucaine, benzocaine and tetracaine were found to inhibit the O2-evolving activity. The inhibitory effect decreases in the order dibucaine greater than benzocaine greater than tetracaine greater than trimecaine similarly as does the potency to inhibit propagation of excitation in nerve fibre. As demonstrated in experiments with artificial donors and acceptors, the site of inhibition is the water-splitting site of PSII. The inhibitory power of the anesthetics grows with increasing ionic strength of the incubating mixture (by adding NaCl or MgCl2) and with pH; this is explained by occurrence of the neutral form of amine. At low concentrations the charged anesthetic acts as a protonofore; however, the inactivation of water splitting is not due to the protonophoric effect. The incubation is followed by the disappearance of ESR signal IIs. The role of Ca2+ and Ca2+-binding protein in PSII electron transport and its localization are discussed.