Effect of the putative cognitive enhancer, linopirdine (DuP 996), on quantal parameters of acetylcholine release at the frog neuromuscular junction.
1. The subcellular mechanism and site of action of linopirdine or DuP 996 (3,3-bis(4-pyridinylmethyl)-1-phenylindolin-2-one) was investigated at the frog neuromuscular junction, using miniature endplate potential (m.e.p.p.) counts and a new method for obtaining unbiased estimates of n (number of functional release sites), p (probability of release), and varsp (spatial variance in p). 2. DuP 996 produced an increase in m (no. of quanta released), which was due to an increase in n and p. The increase in m was concentration-dependent over a range of 0.1-100 microM and completely reversible with 15 min of wash. There was a saturation in the increase in p, but not in the increase in m and n, for [DuP 996] > 10 microM. By contrast, there was no major change in varsp. 3. Block of presynaptic Na(+)- and Ca(2+)-channels with 3 microM tetrodoxin and 1.8 mM Co2+ prevented the m.e.p.p. frequency increase to DuP996, and this effect was completely reversed by washing. 4. Application of the neuronal Ca(2+)-channel blocker, omega-conotoxin GVIA (1 microM) brought about a rapid and profound decrease in the m.e.p.p. frequency increased produced by DuP996. The effect of the toxin was not reversed by prolonged washing. 5. Block of voltage-gated K(+)-channels with 100 microM 4-aminopyridine (4-AP) resulted in only a small (28%) increase in m. The combination of 4-AP (100 microM) and DuP996 (10 microM) produced an increase in m (189%) which was much greater than the sum of the responses to each agent alone.(ABSTRACT TRUNCATED AT 250 WORDS)[1]References
- Effect of the putative cognitive enhancer, linopirdine (DuP 996), on quantal parameters of acetylcholine release at the frog neuromuscular junction. Provan, S.D., Miyamoto, M.D. Br. J. Pharmacol. (1994) [Pubmed]
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