Partial characterization of specific cantharidin binding sites in mouse tissues
The mode of action of cantharidin, the natural vesicant of blister beetles, is examined by radioligand binding studies with mouse tissues. (3H)Cantharidin undergoes specific and saturable binding with the liver cytosol, which is characterized as follows: Kd and Bmax values of 30 nM and 1.8 pmol/mg of protein, respectively; linearity with respect to protein concentration; pH optimum of 6.5 to 7.5; association and dissociation half-times of 20 min and 12 hr, respectively; and 50% inhibition by Mg2+ at 70 microM, Ca2+ at 224 microM, pyrophosphate at 27 microM, and nucleotide triphosphates at 52-81 microM. The binding site undergoes a loss of activity at 45 degrees or higher. The toxicological relevance of this specific (3H)cantharidin binding site of mouse liver cytosol is established in three ways. First, the potency of 15 active cantharidin analogs for inhibiting (3H)cantharidin binding is correlated with their acute toxicity to mice (r = 0.829). Second, 26 related compounds that are inactive in inhibiting (3H)cantharidin binding are also of little or no toxicity to mice. Finally, the binding of (3H) cantharidin to liver cytosol from mice poisoned with increasing amounts of unlabeled cantharidin is inhibited in a dose-dependent manner. (3H)Cantharidin also specifically binds to cytosol fractions of blood, brain, heart, kidney, lung, pancreas, skin, spleen, and stomach. The characteristics of the specific binding site in brain are very similar to those determined in liver with respect to Kd, Bmax, association/dissociation kinetics, and sensitivity to inhibitors. It therefore appears that the toxicity of cantharidin and related oxabicycloheptanes, including the herbicide endothal, is attributable to binding at a specific site in liver and possibly other tissues.
- Research Organization:
- Univ. of California, Berkeley (USA)
- OSTI ID:
- 6924711
- Journal Information:
- Mol. Pharmacol.; (United States), Vol. 33:6
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PROTEINS
BIOCHEMICAL REACTION KINETICS
RECEPTORS
CHEMICAL COMPOSITION
BRAIN
DOSE-RESPONSE RELATIONSHIPS
LIGANDS
LIVER
MICE
RESPONSE MODIFYING FACTORS
STRUCTURE-ACTIVITY RELATIONSHIPS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ANIMALS
BODY
CENTRAL NERVOUS SYSTEM
DIGESTIVE SYSTEM
GLANDS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
NERVOUS SYSTEM
ORGANIC COMPOUNDS
ORGANS
REACTION KINETICS
RODENTS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques