Chemical composition of sarcolemma isolated from rabbit skeletal muscle

Integrity of the alveolar-capillary barrier and alveolar surfactant system in smokers

BACKGROUND

The permeability of the alveolar-capillary barrier to technetium-99m labelled diethylenetriamine pentaacetate (99mTc DTPA) is known to be greatly increased in smokers, but the underlying mechanism is poorly understood. Abnormal permeability of the alveolar epithelium as well as impaired surfactant function has been suggested. The purpose of this study was to examine transudation of urea and albumin into the alveoli and alveolar surfactant function in smokers and non-smokers and to relate these variables to the rate of alveolar-capillary transfer of 99mTc DTPA.

METHODS

Standardised bronchoalveolar lavage was performed and the yield of urea and albumin measured in the lavage fluid. The integrity of the alveolar surfactant system was assessed by measurement of the surface activity and of the yield of phospholipids in alveolar lavage fluid.

RESULTS

The mean decay constant for the pulmonary clearance of 99mTc DTPA was 0.028/min in the smokers and 0.009/min in the non-smokers. The recovery of albumin and urea in alveolar lavage fluid was very similar in the two groups. The surface activity of alveolar lavage fluid was lower in smokers than in non-smokers (minimum surface tension 37.9 versus 28.6 mN/m) and the yield of phospholipids was reduced (2.08 versus 3.86 mg). The rate constant for the pulmonary clearance of 99mTc DTPA correlated with the yield of phospholipids at bronchoalveolar lavage.

CONCLUSIONS

The study shows that increased alveolar-capillary transfer of 99mTc DTPA in smokers is not accompanied by increased transudation of small or large molecules into the alveoli. The findings support the hypothesis that increased clearance of 99mTc DTPA in smokers is related to surfactant dysfunction.

Recoveries of phosphatidylcholine and alveolar macrophages in lung lavage from healthy light smokers

Twenty-one healthy volunteers, 11 light smokers and 10 non-smokers, were studied by broncho-alveolar lavage. The levels of the phosphatidylcholine (PC) in broncho-alveolar lavage were measured and used as an index of surfactant. The PC levels in broncho-alveolar lavage obtained from the smokers were significantly lower than in lavage fluid from the non-smokers. There was an inverse correlation between PC levels and cumulated tobacco smoke exposure, as estimated by the number of pack-years, and to current smoking habits as estimated by the number of cigarettes smoked per day. The number of alveolar macrophages was significantly higher in broncho-alveolar lavage obtained from smokers, and there was a significant inverse correlation between PC levels and numbers of alveolar macrophages in the lavage fluids. The potential role of alveolar macrophages in the elimination of surfactant lipids is discussed.

The membrane lipid and fatty acid composition of erythrocyte ghosts from three patients with paramyotonia congenita

The membrane lipid and fatty acid composition of red blood cell ghosts from three paramyotonia patients was investigated. Cholesterol and total phospholipid contents were not different from the controls, but the sphingomyelin content was reduced, and this was compensated for by an increase in phosphatidylcholine. Thus, the molar ratios of phosphatidylcholine/sphingomyelin and phophatidylcholine/phosphatidylethanolamine were greater than normal. The saturated fatty acids in the total phospholipids were increased so that the ratio of saturated/unsaturated fatty acids was 1.4-1.6 versus 1.1-1.2 in the controls. The polyunsaturated fatty acids comprised only 22-26% of the fatty acids versus 31-32% in controls. The reduction in content of unsaturated fatty acids concerned all phospholipid classes in one patient and only the choline phospholipids in the tow other patients who were related to each other. The pattern of the fatty acids in the C2-position of the glycerophospholipids reflected the finding in the total phospholipids. Thus, an alteration of the activity of the acyl-CoA: 1-mono-acylphosphoglyceride-acyltransferase seems unlikely. The results support the notion of a generalized membrane defect in paramyotonia congenita, although the degree of abnormality in the fatty acid pattern was not correlated with the severity of the clinical symptoms.

Skeletal-muscle sarcolemma from normal and dystrophic mice. Isolation, characterization and lipid composition

1. Mouse skeletal-muscle sarcolemma was isolated, and the preparations obtained from normal mouse muscle and from muscle of mice with hereditary muscular dystrophy were characterized with respect to appearance under the optical and electron microscopes, distribution of marker enzymes, histochemical properties and biochemical composition. 2. The sarcolemmal membranes from normal and dystrophic muscle were subjected to detailed lipied analysis. Total lipid content was shown to increase in sarcolemma from dystrophic mice as a result of a large increase in neutral lipid and a smaller increase in total phospholipids. Further analysis of the neutral-lipid fraction showed that total acylglycerols increased 6-fold, non-esterified fatty acid 4-fold and cholesterol esters 2-fold, whereas the amount of free cholesterol remained unchanged in sarcolemma from dystrophic muscle. Significant increases were found in lysophosphatidylcholine, phosphatidylcholine and phosphatidylethanolamine in dystrophic-muscle sarcolemma; however, the relative composition of the phospholipid fraction remained essentially the same as in the normal case. 3. The overall result of alterations in lipid composition of the sarcolemma in mouse muscular dystrophy was an increase in neutral lipid compared with total phospholipid, and a 4-fold decrease in the relative amount of free cholesterol in the membrane. The possible impact of these changes on membrane function is discussed.

The different fatty acids composition of lecithins in the sarcoplasmic reticulum vesicles and the membranes of adrenal chromaffin granules

Calcium transporting membranes of sarcoplasmic reticulum (SR) and amine transporting membranes of chromaffin granules (AG) isolated from different animal species (ox, rabbit and rat) show similar values for their phospholipid phases (0.5 mumole phospholipids/mg protein). The AG-membranes, however, contain higher lysolecithin (LPC) (10 11%) than the SR-membranes (2-6%). In both types of membrane a characteristic distribution of fatty acids was found in the phosphatidylcholine (PC) fraction. In SR-membranes 18-carbon fatty acids are present in increasing order of unsaturation (18:0 less than 18:1 less than 18:2) and in AG-membranes in decreasing order (18:0 greater than 18:1 greater than 18:2). The fatty acid composition of PCs specific of each membrane seems to be dependent on the presence of different endogenous lysolecithins and suggest a fatty acid turnover in both positions of the PC by the de- and re-acylation cycle. The importance in membranes function with regard to the Ca2+ transport of SR and the amine transport of AG membranes as related to the typical lipid phase is discussed.

The acyltransferase activity of adrenal medulla and sacroplasmic reticulum of skeletal muscles

The presence of acyl-CoA-lysolecithin-acyltransferase was studied in ox adrenal medulla fractionated by sucrose gradient centrifugation. The highest activity of this enzyme is localized in the microsomes and not in the membranes of chromaffin granules. Estimation of acyltransferase activity in fragments of sarcoplasmic reticulum (SR) from rabbit skeletal muscles before and after sucrose gradient centrifugation shows that in these membranes acyltransferase is a membrane bound enzyme. Both enzyme preparations transfer 18-carbon fatty acids in increasing order of unsaturation to 1-acyl-sn-glycer-3-phosphorylcholine (1-acyl-GPC) (18:0 less than 18:1 less than 18:2) and in decreasing order to 2-acyl-sn-glycero-3-phosphorylcholine (2-acyl-GPC) (18:0 greater than 18:1 greater than 18:2). For the acyltransferase present in ox adrenal medulla and fragments of sarcoplasmic reticulum, 1-acyl-sn-glycero-3-phosphorylethanolamine (1-acyl-GPE) is not a good acyl acceptor. The importance of acyltransferase in the de- and re-acylation cycle for the neogenesis of membranes-specific lecithin is discussed.