Salpeter MM. Electron microscope radioautography as a quantitative tool in enzyme cytochemistry. II. The distribution of DFP-reactive sties at motor endplates of a vertebrate twitch muscle.
J Biophys Biochem Cytol 1969;
42:122-34. [PMID:
5786978 PMCID:
PMC2107572 DOI:
10.1083/jcb.42.1.122]
[Citation(s) in RCA: 63] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The distribution of diisopropylfluorophosphate (DFP)-sensitive enzyme sites at the neuromuscular junction was determined quantitatively by electron microscope radioautography after incubation of muscle fragments in DFP-(3)H. Most of the sensitive sites were located in the subneural apparatus at a concentration of 90,000 sites per micro(3) of cleft tissue or 12,000 sites per micro(2) of postjunctional membrane surface area. A considerable concentration is also present in the teloglial cap. It has previously been demonstrated (Rogers et al., 1966) that one-third of the DFP-sensitive sites at the endplate can be reactivated by pyridine-2-aldoxime methiodide (2-PAM)-a compound which selectively reactivates phosphorylated acetylcholinesterase. In the present study, it was found that this ratio of 1:2 holds also on a fine-structural level. Muscle mast cells were found to have a heavy concentration of bound DFP.
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