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The binding of snake venom cardiotoxins to heart cell membranes
Abstract:
Cobra venom cardiotoxins have the effect, inter alia, of causing systolic arrest of the heart. We have observed significant binding in vitro of 35S-labelled cardiotoxins to mouse heart cell membranes. Part of the binding was saturable and could be displaced with homologous unlabelled cardiotoxins but not by neurotoxins or cardiotoxins inactivated by chemical modification. The specifically bound component represented more than 70% of total binding at saturation. Inclusion of Triton X-100 and NaCl in the phosphate-buffered incubation medium prevented nonspecific adsorption to centrifuge tube walls, and gave lower but more reproducible specific binding results, respectively. An apparent dissociation constant of 5 . 10(-7) M and a binding density of 500 pmol toxin/mg membrane protein were derived from the saturation isotherms.
Insights
Cobra cardiotoxins bind specifically to mouse heart cell membranes, suggesting a direct mechanism for their cardiotoxic effects. This binding is saturable and specific, indicating a receptor-like interaction.
Area of Science:
- Biochemistry
- Toxicology
- Cardiovascular Research
Background:
- Cobra venom cardiotoxins are known to induce cardiac arrest.
- The precise molecular mechanisms underlying cardiotoxin activity require further investigation.
Purpose of the Study:
- To investigate the in vitro binding of cobra cardiotoxins to mouse heart cell membranes.
- To characterize the specificity and affinity of this binding interaction.
Main Methods:
- Incubation of 35S-labelled cardiotoxins with mouse heart cell membranes.
- Displacement assays using homologous and heterologous toxins, as well as chemically modified cardiotoxins.
- Optimization of binding conditions using Triton X-100 and NaCl.
- Analysis of binding saturation isotherms to determine binding parameters.
Main Results:
- Significant in vitro binding of cardiotoxins to mouse heart cell membranes was observed.
- A substantial portion (>70%) of this binding was specific, saturable, and displaceable by homologous cardiotoxins.
- Neurotoxins and chemically modified cardiotoxins did not effectively displace the bound cardiotoxins, confirming specificity.
- Optimized conditions yielded reproducible specific binding data.
- An apparent dissociation constant (Kd) of 5 x 10(-7) M and a binding density of 500 pmol toxin/mg membrane protein were determined.
Conclusions:
- Cobra cardiotoxins exhibit specific binding to mouse heart cell membranes.
- This specific binding suggests a potential receptor-mediated interaction contributing to cardiotoxicity.
- The characterized binding parameters provide quantitative insights into the toxin-membrane interaction.