Effects of gossypol acetate on neuromuscular transmission
Abstract
The effects of gossypol acetate on neuromuscular transmission were studied on rat phrenic nerve-diaphragm and frog sciatic nerve-sartorius preparations. Gossypol acetate 15 μg/ml blocked the neuromuscular transmission without affecting the nerve conduction. The amplitude of muscle contraction elicited by direct stimulation was gradually reduced with an elevation of the baseline (tone) by gossypol acetate. The resting membrane potential was not affected by gossypol acetate 25 μg/ml but was reduced to about 84% of the control level by 100 μg/ml. Neostigmine did not antagonize the gossypol neuromuscular blockade. The sensitivity to acetylcholine of the rat chronic denervated diaphragms was not much changed by gossypol acetate. These results supported that gossypol acetate was mainly a presynaptic blocking agent.
Gossypol acetate reduced progressively the amplitude of the end-plate potential (EPP) and its quantal content in Krebs solution with high Mg concentration. But, in curarized preparations, gossypol acetate increased the amplitude of EPP even restored the contractile response in some paralyzed muscle fibers. The frequency of miniature EPP (MEPP) was at first significantly increased and then decreased by gossypol acetate. The highest frequency of MEPP usually occurred after the neuromuscular transmission had already been completely blocked. Moreover, the changes in MEPP frequency induced by gossypol acetate were affected neither in Krebs solution with lower Na (30 mM) or higher Mg (15 mM) concentrations nor in Ca-free medium.
It is surmised that the action of gossypol acetate on the neuromuscular transmission might originate from inhibition of Ca uptake by mitochondria in presynaptic endings.
Keywords:
Gossypol acetate reduced progressively the amplitude of the end-plate potential (EPP) and its quantal content in Krebs solution with high Mg concentration. But, in curarized preparations, gossypol acetate increased the amplitude of EPP even restored the contractile response in some paralyzed muscle fibers. The frequency of miniature EPP (MEPP) was at first significantly increased and then decreased by gossypol acetate. The highest frequency of MEPP usually occurred after the neuromuscular transmission had already been completely blocked. Moreover, the changes in MEPP frequency induced by gossypol acetate were affected neither in Krebs solution with lower Na (30 mM) or higher Mg (15 mM) concentrations nor in Ca-free medium.
It is surmised that the action of gossypol acetate on the neuromuscular transmission might originate from inhibition of Ca uptake by mitochondria in presynaptic endings.