Optical studies of biochemical events in the electric organ ofElectrophorus

Abstract

When slices of the main electric organ of Electrophorus are stimulated electrically, three different effects can be detected optically. These are: (1) A large decrease in absorption evidently due to a decrease of light scattering within the tissue; this change increases gradually with decreasing wavelength. (2) A decrease in absorption which has a definite peak at about 420 nm and is interpreted as arising from oxidation of a haemoprotein. (3) A diphasic (under some conditions triphasic) change in fluorescence emission, interpreted as arising from oxidation/reduction of diphosphopyridine nucleotide. This paper is mainly concerned with an examination of the third of these effects. Identification of the fluorescence response with reduction of DPN was supported by determination of excitation and emission spectra of resting tissue at room temperatures and at the temperature of liquid nitrogen. The emission spectrum of the fluorescence change after stimulation was also determined with a differential spectrofluorometer. The results of the fluorometry agreed well with those obtained by direct chemical analysis. The time course of the fluorescence response and the effect on it of various factors such as amount of stimulation, interval between periods of stimulation, direction of observation, electrical load, temperature, exclusion of oxygen and inhibitors of oxidative metabolism and glycolysis, are described in some detail. A combination of these observations with the results of chemical analyses and thermal studies supports the view that the sequence of events on stimulation of the electric organ is: (1) changes in internal ionic concentrations resulting from the flow of electric current: (2) activation of the sodium pump, driven by phosphate-bond energy and drawing initially on the reservoir provided by creatine phosphate; (3) activation of glycogenolysis to restore the ATP/ADP ratio. The bearing of the changes observed in the DPNH/DPN ratio on the mechanism by which glycogenolysis is controlled is discussed briefly.