Processing of digestive vacuoles in Tetrahymena and the effects of dichloroisoproterenol

Abstract

The digestive-lysosomal system in Tetrahymena has been extensively studied; however, the various vacuole stages and the existence of a required processing period prior to defecation have not been clearly defined. In this study the presence of such a required processing period and the rate of DV defecation in Tetrahymena thermophila were determined. Like the cycle in Paramecium, a digestive cycle in Tetrahymena consisted of two periods: the processing period was 45 min and the defecation period was approximately 2 h, making the complete cycle approximately 3 h. During the defecation period vacuole egestion followed the kinetics of a first-order rate reaction and had a rate constant of 0.0187/min and a t1/2 of 37 min (82 min into the cycle). Using the naphthol AS-TR phosphate-hexazotized rosanilin method to visualize acid phosphatase activity at the light microscopic level, DVs became positive beginning at 10 min. The number of positive DVs increased to a maximum of 13% when DVs were 20-min old and declined to 5-7% beyond 30 min. Although dichloroisoproterenol (DCI) has been reported by others to stimulate vacuole defecation, we found it inhibited the defecation rate. The extent of inhibition depended on the age of the DVs when exposed to DCI. Vacuole formation was completely blocked in cells preexposed to 40 microM DCI for only 10 min; however, upon further exposure, cells could recover from this inhibition. The time required for complete recovery increased with increasing DCI concentrations. If DCI was given to cells simultaneously with latex beads, it was found to exert a dose-dependent inhibitory effect on DV formation.(ABSTRACT TRUNCATED AT 250 WORDS)