Kinetics of monensin-induced swelling of Golgi apparatus cisternae of H-2 hepatoma cells

Abstract

In H-2 hepatoma cells grown in culture, a pattern of response to the sodium-selective ionophore, monensin, was observed in which cisternal swelling commenced at one pole of the Golgi apparatus and was accompanied by the accumulation of swollen vacuoles in the cytoplasm in the absence of a decrease in the number of cisternae per stack. The results suggest that the swollen vacuoles are formed from Golgi apparatus cisternae that are replaced by formation of new cisternae. Depending on monensin concentration, between 2 and 4 such vacuoles accumulated per Golgi apparatus stack within 12.5 min after monensin addition. The rate of vacuole formation was greatest at 10(-6) M monensin and least at 10(-8) M monensin over the range 10(-5) to 10(-8) M monensin. The general pattern of early response to the ionophore is that formation of normal secretory vesicles is blocked, after which the Golgi apparatus continues to function for a time to release membrane as swollen cisternal units that accumulate in the cytoplasm at or near the trans Golgi apparatus face. These phenomena all precede the general swelling response normally observed in glutaraldehyde-fixed animal material and illustrate that the early dynamic responses to monensin are not confined to plant cells.