David S. Campion

Decreased drug binding by serum albumin during renal failure

Abstract By means of an ultrafiltration technique, the capacity of serum from normal subjects and patients with acute and chronic renal failure to bind the azo-dye o -methyl red under physiological conditions was determined. In 29 patients with chronic renal failure the amount of dye bound was 75.0% (SE ± 1.8) compared to 82.5% (SE ± 3.0) in 5 patients with acute reversible renal failure and 89.9% (SE ± 1.0) in 9 healthy volunteers. To examine whether the observed decrease in binding was purely quantitative and due to a concomitant decrease in serum albumin, or was qualitative and due to decreased binding capacity of the albumin molecule, a Scatchard plot of pooled normal sera was established, and individual patient sera were compared to this. In this way molecular interaction was studied and in 20 of the 29 patients with chronic renal failure a qualitative decrease in binding was demonstrable. This was shown not to be due to retained metabolites.

Experimental myotonia and hypocholesterolemic agents

Abstract Three hypocholesterolemic agents which inhibit cholesterol biosynthesis at different stages were administered to rats, and changes in plasma and muscle sterols, erythrocyte membrane (Na + + K + )-ATPase activity and electromyography were measured. Myotonia was induced in rats treated with triparanol (MER-29) and 20,25-diazacholesterol. These drugs block Δ 24 -reductase and cause the accumulation of desmosterol in plasma and muscle. The (Na + + K + )-ATPase activity of the erythrocyte membranes isolated from rats treated with 20,25-diazacholesterol or triparanol was increased. Rats treated with AY9944, a drug which inhibits Δ 7 -reductase and causes the accumulation of 7-dehydrocholesterol but not desmosterol, did not become myotonic. No significant changes in the erythrocyte membrane ATPase activities of these rats were observed. These results support the hypothesis that desmosterol accumulation in muscle is the cause of myotonia induced by 20,25-diazacholesterol and triparanol.

Resting Membrane Potential and Ionic Distribution in Fast- and Slow-Twitch Mammalian Muscle

The resting membrane potential and intracellular potassium and sodium concentration of three guinea pig hind limb muscles were studied. These properties are related to the gross color, the speed of contraction, and the biochemically defined fiber type composing the muscle. The resting membrane potential and intracellular content were: white vastus (grossly white, fast-twitch glycolytic) -85.3 mV. potassium 171.9 meq/liter; soleus (grossly red, slow-twitch oxidative) -69.7 mV, potassium 137.5 meq/liter; and red vastus lateralis (grossly red, fast-twitch oxidative glycolytic) -71.7 mV, potassium 139.6 meq/liter. In soleus and red vastus lateralis, the relative permeability of sodium to potassium was 0.041 and 0.036, while in white vastus it was 0.015. These results give us the first exception to the hypothesis that fast-twitch fibers have higher intracellular potassium and higher resting membrane potential than slow-twitch fibers.

Uric Acid: CHARACTERIZATION OF ITS INTERACTION WITH HUMAN SERUM ALBUMIN

Binding of sodium urate to human serum albumin (HSA) was measured by continuous ultrafiltration at pH 7.4 and ionic strength 0.16 over the concentration range 1-13 mg/100 ml. The percent sodium urate bound to 5 g/100 ml HSA was constant over this concentration range: 30.3 (SE+/-0.6)% being bound at 4 degrees C, 22.6+/-0.3% at 22.5 degrees C, and 19.6+/-0.3% at 37 degrees C. Derived association constants, assuming one binding site were 6.0 x 10(2) M(-1) (4 degrees C), 4.47 x 10(2) M(-1) (22.5 degrees C), and 3.88 x 10(2) M(-1) (37 degrees C).

The effect of a high cholesterol diet on 20,25-diazacholesterol-induced myotonia

Abstract Myotonia induced by 20,25-diazacholesterol may be related to the accumulation of desmosterol which results when 20,25-diazacholesterol inhibits Δ 24 reductase; the increased (Na + + K + )-ATPase observed in this type of myotonia may also be involved. Rats were fed a high cholesterol diet (which inhibited cholesterol and hence desmosterol biosynthesis) and were dosed daily with 20,25-diazacholesterol or water. Corresponding groups were fed a normal diet and dosed with 20,25-diazacholesterol or water. Electromyography, plasma and muscle sterols, and erythrocyte membrane ATPase were measured serially for each group. Drug-treated rats on the normal diet became myotonic within 3 weeks; their plasma and muscle desmosterol were 84 and 69% of the total sterols, respectively. Their (Na + + K + )-ATPase was not significantly increased until 8 weeks of treatment. In contrast, drug-treated rats on the high cholesterol diet never became myotonic; the plasma and muscle desmosterol never exceeded 15%, and the (Na + + K + )-ATPase never exceeded the control level. Changing the high cholesterol diet to normal after 100 days resulted in myotonia within 10 days in the drug-treated rats; while their plasma and muscle desmosterol increased rapidly, no increased ATPase was seen. Reinstituting the high cholesterol diet reversed these sterol changes and abolished myotonia in 2 weeks. We conclude that 20,25-diazacholesterol-induced myotonia can be prevented or reversed by a high cholesterol diet, that the time course of desmosterol accumulation is similar and may be related to the appearance and degree of myotonia, and that the increased (Na + + K + )-ATPase is probably a secondary effect.

Displacement by uricosuric agents of sodium urate bound to human serum albumin.

Abstract The displacement of sodium urate by uricosuric agents from binding sites on human serum albumin (HSA) and normal serum has been demonstrated under physiological conditions in vitro (pH 7.4, ionic strength 0.16) over he oncentration range 1–13 mg/100 ml. At 37°, 0.5 mM sodium salicylate reduced urate bound to 5 g/100 ml of HSA from 19.6 to 9.7 per cent. At 22.5°, 22.6 per cent urate was bound to 5 g/100 ml of HSA, and this was reduced to 12.3 per cent by 0.5 mM salicylate, to 9.2 per cent by 0.5 mM phenylbutazone, to 14.6 per cent by 0.2 mM diflumidone, and to 17.9 per cent by 0.2 mM sulfaethidole. At 22.5°, pooled normal human serum (4.8 g/100 ml of albumin) bound 23.5 per cent urate; with 0.5 mM salicylate present 12.6 per cent urate was bound.

Myotonia induced by single doses of 20,25 diazacholesterol: Increased muscle and plasma desmosterol levels, unaltered (Na+ + K+)-ATPase activity of erythrocyte ghosts☆

Electromyographic myotonia was induced in rats 9 to 12 days after the administration of single doses of 20 to 160 mg/kg 20,25-diazacholesterol. Muscle and plasma desmosterol levels together with the (Na+ + K+)-ATPase activities of the erythrocyte ghosts of these rats were determined at various intervals up to 26 days following drug administration. There was a significant correlation (P < 0.02) between the electromyographic changes and the desmosterol levels in the plasma and muscles of the rats between the ninth and 16th day when myotonia was present. Previous reports have demonstrated that multiple doses of 20,25-diazacholesterol caused an increase in erythrocyte (Na+ + K+)-ATPase activity, but this was not observed in the rats treated with single doses of 20,25-diazacholesterol.

Alteration of muscle and red cell sodium and potassium in 20,25-diazacholesterol-induced myotonia.

Myotonia was induced in rats by a single oral dose of 20,25-diazacholesterol. Myotonia as determined by electromyography developed in 12 days, and was maintained for 20 days. Accompanying the myotonia there was a significant decrease in intracellular sodium that, when compared with controls, was most marked in white glycolytic muscles such as white vastus lateralis [24.6 (se ± 4.3) percentage of decrease (P < 0.005)], and the paraspinal muscles [18.0 (se ± 4.4) percentage of decrease (P < 0.01)], and least in red oxidative muscles such as soleus (3.8 (se ± 4.4) percentage of decrease, not significant). No change in intracellular potassium was observed. The changes in muscles are probably the result of a decreased membrane permeability for sodium. No alteration in serum, or red cell sodium, potassium, or chloride was observed, and (Na+ + K+)ATPase of the red cells remained constant.

The binding of urate to plasma proteins.

Although the etiologic role of microcrystalline monosodium urate monohydrate in the pathogenesis of acute gouty arthritis has been well established, the mechanism by which urate precipitates in joints, soft tissues and the kidneys remains unclear. Some studies have suggested that the solubility of urate is the key factor and that when the solubility of urate in blood synovial fluid and urine is exceeded, urate then precipitates. The question is more complex than this, however, since only approximately 25 per cent of patients with hyperuricemia develop acute gouty arthritis. Furthermore, there is poor correlation between uric acid concentration and the frequency of acute gouty attacks. This has led to speculation that there are factors in serum which are partially responsible for solubilization of urate and that alterations in these factors could be responsible for urate deposition.