Chaetochromin A has been studied in detail with regard to the swelling-inducing effect on mitochondria in vitro to gain insight into the interrelationship between its respiration-impairing and swelling-inducing activities. Chaetochromin A elicited very rapid swelling of mitochondria in isotonic CsCl, RbCl, KCl, NaCl, and LiCl solutions, showing eminent differences in the magnitude and rate of swelling. The swelling amplitude was prominently larger in the KCl medium than those in the other kind of alkali metal chloride media, showing a distinct cation selectivity in the order of K+>>Cs+, Na+, Rb+>>Li+, and a sharp predominant K+-selectivity was observed in the initial rate of swelling. Chaetochromin A was tested for the induction of swelling in the isotonic KCl medium at various pH between pH 5 and 9. The amplitude and velocity of swelling were markedly increased corresponding to the decrease of the pH in the test system. A pH optimum for the swelling induction seemed to locate at much lower pH than the physiological pH range.
