Variations of glycogen: I. Following stimulation of Knollenorgan sensory cells,a lateral line electroreceptor of mormyrid fish

The metabolism of glycogen was studied in sensory cells of the mormyrid fish, Gnathonemus petersii. Knollenorgans, specific cutaneous electroreceptor organs of the lateral line system, have a spontancous electrical activity and their resting discharge in the absence of stimulation is about 0.04 kHz. Various types of stimulation can produce an increase in frequency; the highest frequency (1.30 kHz) is obtained by moving the Knollenorgan above water level. Glycogen was visualized in ultrathin sections after fixation in a solution of potassium ferricyanide and osmium tetroxide. The density of glycogen particles was determined morphometrically in sensory cells before stimulation, after high-frequency activity, and after reimmersion in water. An increase in the electrical activity of the Knollenorgan resulted in a decrease of the glycogen content of sensory cells. The glycogen store was replenished to about 85% of control within 40 min after stimulation and subsequent reimmersion. The results demonstrate that glycogen in the sensory cells of the Knollenorgan represents an energy source which can be catabolized during high electrical activity and replenished during rest.