Biochemical and morphological characterization of subcellular fractions isolated from rabbit colon muscle

Methods of determining plasma and tissue binding of drugs. Pharmacokinetic consequences

The available techniques for the investigation of drug binding to plasma and tissues protein are reviewed and the advantages and disadvantages of the various techniques stated. A comparison of different plasma protein binding techniques is made which shows that the size of the unbound fraction of drug may be influenced by the method used. Protein binding may be assayed by methods including equilibrium dialysis, ultrafiltration, ultracentrifugation, gel filtration, binding to albumin microspheres and circular dichroism. Tissue binding techniques can involve testing binding to isolated organs, tissue slices, homogenates and isolated subcellular particles. Details of the available methods to compute pharmacokinetic constants are given. Stereoselective binding has been investigated for a limited number of drugs and the difference in the binding of 2 enantiomers is usually modest. The measurement of the binding constants is often required to characterise the drug-protein interaction. Mathematical and graphical methods to compute the pharmacokinetic parameters are discussed. The implications of binding on the volume of distribution and clearance of drugs are examined.

Effect of DDE on the Ca metabolism of the duck eggshell gland and its subcellular fractions; relation to the functional stage

Administration of DDE to Indian Runner ducks (Anas platyrhynchos var.) reduced the eggshell index by 28% and the calcium content of the secreted fluid in the shell gland by 25%. DDE inhibited the functional decrease of the calcium content of the gland cells that occurred during eggshell formation. DDE reduced the functional increase in the ATP-dependent binding of Ca2+ to a microsomal subfraction FIII prepared from Ca-secreting glands forming an eggshell. In subfraction FI the Ca2+ binding was decreased by DDE even when the gland contained a mature shell. FIII probably contained calcium-secreting granules, whereas FI contained plasma membrane fragments of the gland cells.

Activation of phosphorylase by anoxia and dinitrophenol in rabbit colon smooth muscle: relation to release of calcium from mitochondria

The effect of anoxia or 2,4-dinitrophenol (DNP) on the phosphorylase a activity and the calcium content in subcellular fractions from rabbit colon smooth muscle was studied. Anoxia for 15 min. as well as DNP (6.6 X 10(-5) M) for 5 min. increased the phosphorylase a activity. The calcium content in the mitochondrial subfraction, prepared from the anoxic- or DNP-treated intact muscle and determined by atomic absorption spectroscopy, was reduced. The calcium content in the nuclear and the microsomal fractions was not changed in preparations with a normal Ca-content. When the muscle was incubated for 60 min. in a Ca2+-free medium containing 2.0 mM EGTA, the calcium content in the mitochondrial fraction was reduced to 38% of the control. This calcium level was still further reduced and the phosphorylase a activity was increased by DNP in this "Ca-poor" muscle. In these preparations the Ca-content of the microsomal + supernatant fraction increased. Only when the muscle was incubated, initially, in an anoxic medium containing 0.1 mM Ca2+ for 120 min. and, subsequently, in an oxygenated medium containing 0.1 mM Ca2+ for 20 min., DNP failed to activate phosphorylase and to decrease the calcium content in the mitochondrial fraction. These results indicate that mitochondrial Ca2+ release is one of the regulatory factors of the anoxic-induced glycogenolysis.

Effect of p-p'-DDE administered in vivo and in vitro on Ca2+ binding and Ca2+-Mg2+-ATPase activity in egg shell gland mucose of ducks

Thinning of the egg shell is produced by p-p'-DDT and DDE in several species of birds. A study was made of the effect of DDE administered in vitro and in vivo on the Ca2+ binding and Ca2+-Mg2+-activated ATPase of a homogenate of the egg shell gland of ducks (Anas platyrhynchos var.). The concentration of Ca2+ was 1 X 10(-4) M and that of MgATP 1 X 10(-3) M. In vitro, DDE in concentrations of 2-16 micrograms/ml of incubation medium inhibited the Ca2+-Mg2+-activated ATPase in a concentration-dependent manner, whereas Mg2+-activated ATPase was not affected by these concentrations. The Ca2+ binding by the homogenate was reduced by DDE in the same concentrations. The sodium azide sensitive Ca2+ binding was most sensitive. In vivo, DDE administered in a concentration of 40 mg/kg dry weight of the food for 45 days reduced the egg shell index by 18% in comparison to controls. After 45 days of treatment the DDE concentrations in the egg shell gland mucosa was 1.20 +/- 0.16 micrograms/g of wet weight, while no DDE was detected in the controls. The Ca2+-Mg2+-activated ATPase was reduced by 32%, whereas the Mg2+-ATPase was not changed. The Ca2+ binding by the homogenate was reduced by 29%, the sodium azide sensitive part being most vulnerable, DDE increased the total Ca content of the egg shell gland mucosa by 44%. Since Ca is transported against a concentration gradient between blood plasma, and the lumen of the shell gland, it is suggested that DDE, by inhibiting the Ca2+-Mg2+-activated ATPase, decreased the Ca translocation over the egg shell gland mucosa.

Comparison of p-p'-DDE and o-p'-DDE on eggshell thickness and Ca binding activity of shell gland in ducks

One of the main ecotoxicological effects of DDT and its stable metabolite DDE is to reduce the reproductive success in several species of birds by decreasing the thickness of the eggshell. In two different strains of ducks (Anas platyrhynchos var.) addition of 40 mg/kg dry weight of p-p'-DDE to the diet for 45 days produced a significant and long-lasting reduction of the shell thickness, measured as eggshell index. The reduction was more marked in Indian Runner Ducks (IRD; 30 +/- 3%) than in a Swedish X Rouen breed (SR; 10 +/- 2%. The p-p'-DDE residues in the egg yolk + egg white were almost similar in the two strains; 38 +/- 2 and 51 +/- 6 p.p.m. (wet weight) respectively. In the IRD 40 mg/kg of o-p'-DDE in the diet for 45 days was much less potent in reducing the eggshell index (8 +/- 3%) than the p-p' isomer; the amount of residue of the o-p' isomer in the eggs (2.2 +/- 0.1 p.p.m.) was also smaller. A homogenate of the shell gland from the SR breed accumulated 45Ca2+ in the presence of ATP. The accumulation was inhibited about 50% by 5 mM sodium azide and 100% by 3 mM mersalyl. p-p'- and o-p'-DDE in the incubation medium both reduced the Ca2+ binding, in a similar and dose-dependent manner. The threshold concentration was about 20 p.p.m.; 40 p.p.m. reduced the accumulation by about 40%. DDE may reduce eggshell thickness by inhibiting the Ca binding to the membranes of the cells of the eggshell gland.