The Swelling of Rat Liver Mitochondria by Thyroxine and its Reversal

Abstract

The in vitro swelling action of L-thyroxine on rat liver mitochondria as examined photometrically represents an acceleration of a process which the mitochondria are already inherently capable of undergoing spontaneously, as indicated by the identical kinetic characteristics and the extent of thyroxine-induced and spontaneous swelling, the nearly identical pH dependence, and the fact that sucrose has a specific inhibitory action on both types of swelling. However, thyroxine does not appear to be a "catalyst" or coenzyme since it does not decrease the temperature coefficient of spontaneous swelling. The temperature coefficient is very high, approximatNy 6.0 near 20 °.Aging of mitochondria at 0 ° causes loss of thyroxine sensitivity which correlates closely with the loss of bound DPN from the mitochondria, but not with loss of activity of the respiratory chain or with the efficiency of oxidative phosphorylation. Tests with various respiratory chain inhibitors showed that the oxidation state of bound DPN may be a major determinant of thyroxine sensitivity; the oxidation state of the other respiratory carriers does not appear to influence sensitivity to thyroxine. These facts and other considerations suggest that a bound form of mitochondrial DPN is the "target" of the action of thyroxine.The thyroxine-induced swelling is not reversed by increasing the osmolar concentration of external sucrose, but can be "passively" or osmotically reversed by adding the high-particle weight solute polyvinylpyrrolidone. The mitochondrial membrane becomes more permeable to sucrose during the swelling reaction. On the other hand, thyroxine-induced swelling can be "actively" reversed by ATP in a medium of 0.15 M KC1 or NaC1 but not in a 0.30 ~ sucrose medium. The action of ATP is specific; ADP, Mn +*, and ethylenediaminetetraacetate are not active. It is concluded that sucrose is an inhibitor of the enzymatic relationship between oxidative phosphorylation and the contractility and permeability properties of the mitochondrial membrane.Occurrence of different types of mitochondrial swelling, the intracellular factors affecting the swelling and shrinking of mitochondria, as well as the physiological significance of thyroxine-induced swelling are discussed.

Exchange of potassium ions across a concentration difference by isolated rat-liver mitochondria

“…About half the protein of mitochondria is released in soluble form on disrupting the particles (Hogeboom & Schneider, 1950;Spector, 1953). Furthermnore, the swelling of mitochondria can be prevented or reversed by adding colloids to the medium, whereas sucrose is ineffective (Lehninger, Ray & Schneider, 1959). Therefore isolated mitochondria may tend to swell if their limiting membranes become permeable to sucrose and salts while remaining impermeable to colloids.…”

Studies of copper ion-induced mitochondrial swelling in vitro

“…At this concentration of ATP, Mg2+, EDTA or bovine serum albumin did not potentiate, though at ATP concentrations less than 3-3mM Mg2+ or serum albumin+EDTA slightly enhanced the ATP-induced contraction. Lehninger (1959), in a detailed study ofthe action of ATP in causing the reversal of thyroxine-induced swelling of rat liver mitochondria, observed that sucrose added to the basal tris-potassium chloride medium inhibited the swelling and ATP reversal, suggesting a common denominator in these two events. Fig.…”

An Electron Microscopic Study on the Morphological Changes of Isolated Rat Liver Mitochondria by Aging

“…Measurement of swelling of the mitochondria with absorbance at 520 mg The swelling of the mitochondria in the course of aging in 0.25 M sucrose (pH 7.4) at 4°C was measured by absorbance changes at 520 mg using Beckman model DU spectrophotometer every 24 hours until 20 days. The stock suspension was diluted with 0.25 M sucrose (pH 7.4) to yield an initial absorbance between 0.80 and 1.00 (10). Fig.…”