Changes in the phospholipid content of intact mitochondria under mitochondrial swelling in hypotonic sucrose solutions]

Mitochondrial swelling in hypotonic sucrose solutions is accompanied by a decrease of the amount of phosphatidyl ethanolamines, cardiolipids and their lyso-derivatives. An addition of dicaine (inhibitor of phospholipase) to the incubation medium results in a considerable decrease of mitochondrial swelling and prevents the decay of phosphatidyl ethanolamines and cardiolipids. This effect is due to the inhibition of corresponding phospholipases. The data obtained suggest that the passive mitochondrial swelling is accompanied by activation of endogenous phospholipases and by a hydrolysis of cardiolipids, phosphatidyl ethanolamines and their lyso-derivatives.     

Characteristics of thyroxine swelling in skeletal muscle mitochondria: Relationship to valinomycin swelling and swelling in the absence of Mg2+

Summary Divalent cation-depleted skeletal muscle mitochondria undergo energy-dependent swelling in the presence of thyroxine analogues+Mg²⁺, as well as in the presence of valinomycin or the absence of Mg²⁺. ATP-supported swelling shows a K⁺-specificity in the presence of thyroxine analogues or valinomycin, in contrast to a Na⁺-specificity in the absence of Mg²⁺. Substrate-supported swelling shows a K⁺-specificity in the presence of valinomycin but fails to show an alkali metal cation specificity under the other two swelling conditions. All three kinds of swelling show a permeant anion dependency. Although Mg²⁺ inhibits the swelling which occurs in its absence and also inhibits uncoupling of respiration, even in the presence of valinomycin, nevertheless Mg²⁺ does not inhibit the energy-dependent swelling which occurs in the presence of valinomycin or thyroxine analogues. The findings show that thyroxine does not promote swelling simply because it chelates Mg²⁺. Rather, they show that thyroxine promotes a selective change in accessibility of monovalent cations. They suggest that thyroxine in the presence of Mg²⁺ acts at the first coupling site as an electron ccepptor. An observed inhibition of oxygen uptake would appear to be explained on the basis of thyroxine in higher concentration acting as an electron sink. The findings suggest that, as with the lipid-soluble K⁺ carrier, valinomycin, in the presence of Mg²⁺, a change in the status of electrical gradients in the membrane can account for the osmotic swelling observed in the presence of thyroxine analogues.Contribution No. 346 from the Animal Research Institute, Canada Department of Agriculture, Ottawa, Canada.     

Role of swelling in muscle contraction

The two types of volume change occurring in muscle and in contractile protein systems have been defined. Theoretical examination has been made of the influence of hydrophobic group interactions upon these two volume changes. Three different contractile mechanisms have been proposed in which osmotic changes can occur. The most plausible mechanism for striated muscle does not require a cell membrane and can effect a load-sensitive division of energy between direct pull and lateral swelling.     

The swelling of biocolloids

Summary Illumination with ultraviolet rays of agar-agar in the dry state, was found to influence considerably the swelling of agar-agar in distilled water.     

Unusual swelling of elastin

The swelling behavior of the elastin network has been investigated by comparing the linear expansion of samples of purified elastin with the volume expansion of the network, calculated on the basis of composition. Elastin sample dimensions and sample masses were measured under three conditions in which volume changes: thermal expansion at fixed water contents, deswelling due to dehydration, and swelling to greater than normal levels due to the swelling agent, sodium dodecyl sulfate. Isotropic network swelling usually changes length in proportion to the cube root of network volume, but length was found to be directly proportional to volume, showing a greater increase in length than expected. This unusual swelling behavior is attributed to an unusual elastin structure at the subfiber level, but there is insufficient detail on elastin's molecular organization to identify a mechanism to explain how it occurs. Assuming the network swells homogeneously, we describe two models that correctly predict swelling behavior, but these models imply a significant deviation from the structure generally assumed for an elastomeric polymer network of kinetically free molecular chains. Assuming that the network swells heterogeneously removes part of the difficulty with the models, but the observed direct proportionality between length and network volume remains to be explained.     

Ammonia-induced astrocyte swelling in primary culture

The effect of ammonia on water space of astrocytes in culture was determined as a means of studying the neurotoxicity of ammonia in fulminant hepatic failure (FHF). Treatment of primary astrocyte cultures obtained from neonatal rat cortices with 10 mM NH₄Cl for 4 days resulted in a 29% increase in astrocytic water space, as measured by an isotopic method utilizing 3-O-methyl-[³H]-glucose. this effect was time- and dose-dependent. The ammonia-induced swelling was reversible as the water space in cultures treated with 10 mH NH₄Cl for 3 days, and then returned to normal culture media for 1 day, was similar to control cultures. These findings suggest that elevated levels of ammonia lead to astrocyte swelling and may contribute to the brain edema in FHF.Special issue dedicated to Dr. Santiago Grisolia     

The temperature-dependent swelling of elastin

It is suggested that the temperature-dependent swelling behavior of water-swollen elastin is due entirely to the interaction of the numerous nonpolar groups in the elastin protein wiht the aqueous swelling solvent (i.e., ahydrophobic interaction). Flory-Rehner theory for network swelling was used to test this hypothesis. Calculated values for the solvent–polymer interaction parameter, χ1, derived from swelling data indicate that water is a very poor solvent for elastin at all temperatures over the range 0–70° C. Comparison of the calculated _χ1 values with theoretical values for the free energy of interaction of nonpolar solutes and water strongly suggests that the swelling behavior of elastin can be attributed quantitatively to hydrophobic interactions. The implications of these results for the structure and elastic mechanism of elastin are discussed.