Regulation of Intravesicular pH and Development of Botulinum Intoxication.
Abstract
Botulinum and tetanus toxins are thought to enter cells through endocytotic vesicles where acidification is required for release of these toxins into the cytoplasm. The role of vesicular acidification in the development of botulinum intoxication was studied n the isolated mouse phrenic nerve/diaphragm muscle preparation. A number of compounds that reportedly block acidification by the vesicular H+-ATPase were tested for their inherent toxicity and their ability to block botulinum-induced synaptic failure. ATP uncoupling agents (CCCP and FCCP) and a protein modifying agent (NBD-Cl) caused muscle rigor and synaptic failure in isolated muscle tissue. The least toxic compounds tested were two ionophores, nigericin and monensin, that increase membrane permeability to H(+) and K(+) or H(+), Na(+) and K(+) respectively. These ionophores block vesicle acidification by acting as H(+) shunts to neutralize pH gradients across vesicular and other membranes. Of the two drugs, nigericin showed the least toxicity with no loss of muscle contractility and only a slow block of synaptic transmission when applied at concentrations below 100 nM. Concentrations of nigericin < or = 10 nM showed no inherent toxicity. Nigericin treatment (40 nM) of a botulinum type A or B (10(-10) to 10(-9) M) exposed diaphragm delayed development of blockade 2- to 3-fold over onset times in unprotected muscles. This delay in onset was roughly equivalent to a 10-fold reduction in the effective concentration of botulinum toxin. Neutralization of endocytotic vesicles was thus able to delay onset and reduce the effective concentration across botulinum toxin serotypes.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 13, 1993
- Accession Number
- ADP008891
Entities
People
- R. E. Sheridan
Organizations
- United States Army Medical Research Institute of Chemical Defense