3 alpha-Hydroxy-5 beta-pregnan-20-one sulfate: a negative modulator of the NMDA-induced current in cultured neurons.
We have shown previously that the neurosteroid pregnenolone sulfate acts as a positive allosteric modulator at the N-methyl-D-aspartate (NMDA) receptor while inhibiting the kainate, the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), the glycine, and the gamma-aminobutyric acid (GABA) responses of chick spinal cord neurons. Here, we report that 3 alpha-hydroxy-5 beta-pregnan-20-one sulfate (5 beta 3 alpha S), a sulfated form of naturally occurring 5 beta 3 alpha, inhibits both the NMDA and the non-NMDA receptor-mediated responses as measured by whole cell voltage clamp recordings. 100 microM 5 beta 3 alpha S rapidly and reversibly inhibits the response to 30 microM NMDA by 66%, 50 microM kainate by 37%, and 25 microM AMPA by 29%. Application of 50 microM nonsulfated 5 beta 3 alpha does not produce any significant effect on the NMDA response, demonstrating that the sulfate moiety is important for the effect of 5 beta 3 alpha S on the NMDA response. The effect of 5 beta 3 alpha S on the NMDA response is concentration dependent, with an EC50 of 62 microM. 5 beta 3 alpha S reduces the maximum NMDA response with little effect on the NMDA EC50, indicating that antagonism of the NMDA response by 5 beta 3 alpha S is noncompetitive. The fact that 5 beta 3 alpha S inhibition of the NMDA response is neither agonist nor voltage dependent demonstrates that 5 beta 3 alpha S does not act as an open channel blocker. Furthermore, inhibition of the NMDA response by 5 beta 3 alpha S is not reduced by the addition of a maximal concentration (10 microM) of glycine, indicating that 5 beta 3 alpha S does not act via the glycine recognition site. The inhibitory action of 5 beta 3 alpha S on the NMDA and non-NMDA receptors may provide a basis for inhibiting glutamate receptor-induced seizures and excitotoxic cell death.
Park-Chung
M
M
Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Massachusetts 02118.
Wu
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D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D016291:Dizocilpine Maleate / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects; D007536:Isomerism; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D011280:Pregnanolone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects*
D007473:Ion Channels; D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate; C019427:3-hydroxypregnan-3-one 3-sulfate; D011280:Pregnanolone