Active Ca Transport of Sarcoplasmic Reticulum during Experimental Uremia. Changes in Kinetics and Lipid Composition

Abstract

The Ca-transport system of sarcoplasmic vesicles of rabbits is altered by experimental uremia. 1. The influx rate constant of the experimental membranes decrease with a resulting decrease of the calcium influx rate.2. The experimental membranes transport a smaller amount of Ca2+ per mol of ATP split than the controls, i.e. their transport ratio is decreased.3. The calcium permeability of the experimental membranes increases with a resulting decreased concentrating ability.4. The phosphatide content but not the cholesterol content of the experimental membranes dccreases with a consequent increase of the cholesterol/phosphatide ratio.5. The fatty acid pattern of total phosphatides of the experimental membranes changes. A relative decrease of palmitic acid and oleic acid occurs and a relative increase of stearic, arachidonic and higher unsaturated fatty acids.6. The altered lipid composition of the membranes does not change the temperature dependence of the kinetics, In recent years it was shown that function and membrane composition of the fragment sarcoplasmic reticulum are affected by different models of disease showed kinetic changes of the sarcoplasmic reticulum during experimental uremia. In the following study these changes are analyzed in detail. Alterations of the lipid-protein interactions of the membrane were found which might be relevant for the understanding of disturbances of active transport processes during uremia.The changed lipid-protein interactions, correlated with kinetic changes, represent a new model of these interactions within intact membranes of fragmented sarcoplasmic reticulum which until now was not available in vifro and thus might allow some more insight into the lipid-protein interactions of the membrane. MATERIALS AND METHODSRabbits (2 -2.5 kg) of either sex were made uremic by 516 nephrectomy (removal of the right kidney, ligation of pole arteries of the left kidney under nembutal anaesthesia in one session. Control animals were sham operated. After the operation the rabbits were kept on pair-feeding conditions and sacrified after 7 days. During this time the serum urea level rose from 41.2 k 5.8 mg% to above 80 m g x .The vesicles were prepared from the psoas muscle and the white muscles of the hind legs according to Nagai et al. [9]. Neither a higher degree of protein nor of mitochondria1 impurities of the pathological preparations could be detected by gel-electrophoresis (Fig. I), electron microscopy (courtesy of D r Agostini) or by means of sodium azide, 5 mM of which showed no depressive action on the ATPase activity in both preparations.The ATPase activity of the vesicles was recorded by a pH stat instrument (Radiometer, Copenhagen) which was standardized by parallel P, measurements according to Rockstein and Herron [lo]. The Catransport activity was measured by the millipore filtration technique. For special conditions of the different kinetic measurements see legends.The vesicle lipids were extracted with a 20-fold amount of chloroform/methanol (2/1) and washed according t...

Effect of Chronic Renal Failure on Respiratory Muscle Strength

“…This, too, was reversed by vitamin D replenish ment. That these abnormalities also apply to uremia has been demonstrated by Heimberg et al [10] and others [8] in uremic rabbits. In these studies the reduc tion in all parameters of calcium transport by the sarcoplasmic reticulum reversed on the administration of l,25(OH)D3 and was unrelated to the nutritional status or level of parathyroid hormone.…”

“…It has recently been confirmed that res piratory muscle weakness occurs in under nourished patients [1] and in certain sys temic disorders, such as systemic lupus erythematosus [2], myasthenia gravis [3], and hypothyroidism [4], Respiratory mus cle weakness was also reported by Aubier et al [5] in patients with hypophospha temia and in dogs with hypocalcemia [6], Although skeletal muscle weakness and myopathies have been reported in patients [7][8][9] and in experimental animals [10,II] with chronic renal failure, respiratory muscle function in patients with chronic renal failure has not been investigated. Therefore, the purpose of this study was to assess the effects of chronic renal failure (C'RF) in patients with normal pulmonary function undergoing hemodialysis on re spiratory muscle strength and maximum voluntary ventilation (M W ), an index of muscle endurance [1 ].…”

Reversal of decreased phosphorylation of sarcoplasmic reticulum calcium transport ATPase by 1,25-dihydroxycholecalciferol in experimental uremia

“…The calcium uptake was studied at room temperature using the following standard conditions as described before [15]: 5 mM ATP" 10 mM MgCI2; 20 mM histidine, pH 7.0; 40 mM KCI; 5 mM oxalate; 0.1 mM CaCI.2 ( + 4'5CaC12); 0.05 mg vesicular protein/ml. Under these conditions, calcium uptake is optimally activated and is not affected by small variations of the concentrations of ionized calcium in the medium.…”

“…Calcium uptake in sarcoplasmic reticulum vesicles isolated from vitamin D-deficient muscle was found to be diminished [12][13][14]. Impaired calcium kinetics in the SR of skeletal muscle [15] and myocardium [16] were previously observed in uremia, a state of presumed absolute deficiency of 1,25(OH)2D3. This effect was not related to increased blood urea concentrations, metabolic acidosis, secondary hyperparathyroidism, or malnutrition.…”

Uraemic Myopathy: Fact or Fiction

“…Impaired excitation-contracting coupling has been suggested by Brautbar (3) on the basis of the work of Heimberg et al (4), who found markedly reduced calcium ion transport by the sarcoplasmic reticulum. As calcium release from the sarcoplasmic reticulum is of critical importance in the sequence leading from excitation to contraction, these findings led Brautbar to conclude, from biochemistry and not physiological measurements, that dialysis patients have excitation-contraction coupling abnormalities.…”