ABSTRACT
We have cloned P2X4, a member of the P2-purinoceptor family, which has a new pharmacological profile. Rat P2X4 is distantly related to P2X1, P2X2 and P2X3 and is expressed in brain, spinal cord, lung, thymus, bladder, adrenal, testis and vas deferens. This ligand gated ion channel is activated by ATP and analogs with the potency order of ATP > ATP gamma S > 2-methylthio ATP > ADP approximately alpha beta-methylene ATP. However, none of the currently used P2X purinoceptor antagonists suramin, reactive blue 2 and PPADS blocked ATP evoked currents; in contrast their application resulted in potentiation of the agonist response. Due to lack of any known antagonist for P2X4 it is unlikely that native P2X4 has previously been recognized as a P2X purinoceptor.
Subject(s)
Adenosine Triphosphate/analogs & derivatives , Adenosine Triphosphate/pharmacology , Brain/metabolism , Ion Channels/physiology , Receptors, Purinergic P2/physiology , Spinal Cord/metabolism , Adrenal Glands/metabolism , Amino Acid Sequence , Animals , Conserved Sequence , Cysteine , DNA, Complementary , Female , Hippocampus/metabolism , In Situ Hybridization , Ion Channel Gating , Ion Channels/biosynthesis , Ion Channels/drug effects , Kinetics , Lung/metabolism , Male , Membrane Potentials/drug effects , Molecular Sequence Data , Oocytes/drug effects , Oocytes/physiology , Organ Specificity , Rats , Receptors, Purinergic P2/biosynthesis , Receptors, Purinergic P2/drug effects , Receptors, Purinergic P2X4 , Sequence Homology, Amino Acid , Suramin/pharmacology , Testis/metabolism , Thymus Gland/metabolism , Vas Deferens/metabolismABSTRACT
The N-methyl D-aspartate (NMDA) receptor subtype of glutamate-gated ion channels possesses high calcium permeability and unique voltage-dependent sensitivity to magnesium and is modulated by glycine. Molecular cloning identified three complementary DNA species of rat brain, encoding NMDA receptor subunits NMDAR2A (NR2A), NR2B, and NR2C, which are 55 to 70% identical in sequence. These are structurally related, with less than 20% sequence identity, to other excitatory amino acid receptor subunits, including the NMDA receptor subunit NMDAR1 (NR1). Upon expression in cultured cells, the new subunits yielded prominent, typical glutamate- and NMDA-activated currents only when they were in heteromeric configurations with NR1. NR1-NR2A and NR1-NR2C channels differed in gating behavior and magnesium sensitivity. Such heteromeric NMDA receptor subtypes may exist in neurons, since NR1 messenger RNA is synthesized throughout the mature rat brain, while NR2 messenger RNA show a differential distribution.