RESEARCH ON THE GLUTAMATE GATED CHANNELS IN THE NEUROSECRETORY CELLS OF MTXO IN THE EYESTALKS OF ERIOCHEIR SINENSIS

The X-organ sinus gland is a major peptidergic neurosecretory system in crustacean,analogous to the vertebrate hypothalamoneurohypophyseal system.Chinese mitten-handed crab ( Eriocheir sinensis )X-organ located on the ventral surface of terminalia in the eyestalk,named MTXO.Three types of neurosecretory cells dissociated from MTXO had been identified on the basis of shape,size and outgrowth fashion.The cell type A and cell type B were immunoactive to anti-CHH and anti-MIH serum respectively.In the present paper,the whole-cell patch clamp technique was used to examine the responses of MTXO neurosecretory cells to rapid application of glutamic acid(Glu)and the Glu receptor characteristics.The results suggested that glutamate activated a ionotropic Cl- channel receptor and evoked depolarization or hyperpolarization in the type A and type B neurosecretory cells in response to the Glu (1mmol/L)depending on the [Cl-]0/[Cl-] i ratio.Under voltage clamp mode,the transient inward Cl- channel currents(IGlu )were resolved in responses to Glu(0.01—5mmol/L).The size of Glu currents were related to the Glu concentration,Dose-responses curve showed line shape,with a just-discernable effect at 0.01mmol/L and near-saturation at 5mmol/L. During continued Glu perfusion, the responses declined more quickly for higher concentration.When the desensitization had occurred,it could not be overcome by application of higher concentration.The recovery required 20s for type A and type B cells after washing with standard extracellular solution.The Glu currents had reversal potentials that followed Nernst Cl- potentials when [Cl-] was varied.The pharmacological results revealed that the GABA receptor of the crab neurosecretory cells were sensitive to the Cl- channel blocker picrotoxin(0.5mmol/L),insensitive to ionotropic Glu receptor agonist,Quisqualate、Kainate、NMDA、AMPA.Ibotenic acid (IA)was proved to be an effective agonist on the cell type A and B,producing inward currents that showed rapid desensitization similar to the Glu responses.The responses to Glu were attenuated after application of IA,showed cross-desensitization between IA and Glu.No response was observed in the crab MTXO cells after application of Glycine.Some evidence revealed that Glu and GABA activated different receptors.This suggests that the neurosecretory cells were regulated by CNS through different Glu and GABA system.