对虾的慢与快牵张感受器的放电型式与镁离子浓度的关系

对虾的慢适应和快适应感受器的放电型式可因环境中 Mg~( )浓度的改变而发生转变:在用蔗糖代替全部 Mg~( )的海水(无镁海水)中,当感受器肌肉受到持续性牵拉时,两种感受器都发出持续性节律放电,即快感受器也给出了慢适应型放电;反之,在 Mg~( )浓度加倍的海水(高镁海水)中,两者都只在感受器肌肉受到牵拉的瞬时给出短暂的放电,即慢感受器也给出了快适应型放电。这种放电型式的转变只有当无镁或高镁海水接触感受器细胞体时才出现。在正常海水中,10~(-3)M 的γ-氨基丁酸(GABA)即可完全抑制由牵拉引起的对虾牵张感受器的放电,但在无镁海水中,必需10~(-2)M GABA 方能达到同样的抑制效果。若在无镁亦无钙海水中,即使用1M 的 GABA 亦不能抑制感受器的牵拉放电。不仅如此,在这种海水中抑制神经对感受器细胞放电的抑制作用也消失。

DEPENDENCE OF DISCHARGE PATTERNS OF SLOW AND FAST STRETCH RECEPTORS OF Penaeus orientalia ON Mg~( )CONCENTRATION

During maintained stretch,both slow and rapid adapting stretch receptors of sea shrimp Penaeus orientalis showed continuously rhythmic or tonic dischargepattern when normal sea water was replaced by Mg~( )-free medium.When theMg~( )concentration of the perfusion sea water was doubled both types of stretchreceptors showed rapid adapting or phasic discharge.Such changes of dischargepattern could also be observed in the in vivo preparation when filter paper soakedwith modified sea water was placed on the receptor cells.Gamma-Aminobutyric acid(GABA)concentration of 10~(-3)M completelyinhibited stretch discharge of the receptors,but more than 10~(-2)M of GABA wasneeded to suppress stretch discharge when the preparation was maintained inMg~( )-free sea water.Even at concentration of 1 M no inhibitory effect of GABAcould be observed when the receptor preparation was perfused with both Mg~( )and Ca~( )-free sea water.In this medium reflex inhibition of the receptors wasalso abolished completely.