The actions of 3,4-diaminopyridine in bullfrog sympathetic ganglia
1982; Elsevier BV; Volume: 252; Issue: 2 Linguagem: Inglês
10.1016/0006-8993(82)90395-x
ISSN1872-6240
AutoresBrian Apatoff, William K. Riker,
Tópico(s)Nicotinic Acetylcholine Receptors Study
ResumoThe effects of 3,4-diaminopyridine (3,4-DAP) on isolated sympathetic ganglia were studied by means of intracellular and extracellular recording techniques. 3,4-DAP in micromolar concentrations caused a single orthodromic stimulus to generate a brief burst of repetitive postganglionic discharges. Such stimulus-bound repetition (SBR) appeared to represent a presynaptic action of 3,4-DAP, as no repetitive firing could be evoked by antidromic or direct stimulation of ganglion cells. 3,4-DAP also increased the latency to the onset of the synaptic potential at concentrations paralleling those responsible for SBR. The actions of 3,4-DAP on synaptic transmission extended over a 10,000-fold concentration range, beginning with synaptic facilitation at micromolar concentrations (1–500 μM), and proceeding to depressant effects at millimolar concentrations (0.5–10 mM). The postganglionic repetitive discharges (SBR) induced by 3,4-DAP could be selectively suppressed by d-tubocurarine (d-Tc) or tetraethylammonium (TEA), at concentrations of these antagonists below those required to block transmission. 3,4-DAP had significant anti-curare effects, producing a four-fold shift of the d-Tc concentration-effect curve for transmission block. In contrast, 3,4-DAP neither antogonized nor enhanced the transmission block produced by TEA. These results are incompatible with traditional concepts of ganglionic blockade by d-Tc and TEA, and suggest the possibility of presynaptic sites of action in ganglion block.
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