Abstract
The P 2 purinoceptor antagonist suramin reverses skeletal muscle paralysis evoked by non-depolarizing neuromuscular blocking agents in vitro and in vivo. To further study the action of suramin on neuromuscular transmission, (miniature) endplate potentials ((m.)e.p.ps), motor nerve terminal currents and the release of radiolabeled acetylcholine was measured in isolated nerve-muscle preparations. In preparations paralysed by low Ca 2+ high Mg 2+ conditions, suramin (10 μM-1 mM) induced a concentration-dependent decrease in quantal content of the e.p.ps without affecting m.e.p.ps. Suramin reversed neuromuscular block by d-tubocurarine in these preparations. In erabutoxin paralysed preparations, suramin (40 μM-1 mM) inhibited the motornerve terminal currents related to Ca 2+ influx concentration-dependently, but did not affect Na + currents. Suramin-induced inhibition of Ca 2+ currents was not antagonized by ATPγS. Suramin (300 μM) reduced [ 14C]acetylcholine outflow in non-paralysed rat phrenic nerve-hemidiaphragm preparations by 32%. As suramin did not chelate Ca 2+, these results indicate that suramin inhibits neuromuscular transmission by blocking prejunctional Ca 2+ channels, thereby decreasing acetylcholine release upon nerve stimulation.
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