Inhibition by suramin and reactive blue 2 of GABA and glutamate receptor channels in rat hippocampal neurons

Abstract

Effects of suramin and reactive blue 2 (RB2), compounds known as antagonists at P2-purinoceptors, on ionic currents mediated through GABA and glutamate receptor channels were investigated in rat hippocampal neurons. Under whole-cell voltage-clamp, suramin (30 to 300 microM) and RB2 (10 to 100 microM) inhibited a current activated by 10 microM GABA in a concentration-dependent manner. Suramin (100 and 300 microM) and RB2 (10 and 30 microM) also inhibited an inward current activated by kainic acid (100 microM), an agonist at non-NMDA type glutamate receptor channels, and an inward current activated by N-methyl-D-aspartate (NMDA; 100 microM), an agonist at NMDA type glutamate receptor channels. The inhibition by suramin or RB2 did not exhibit voltage-dependence between -30 and -90 mV in the case of the GABA- or the kainate-evoked current. In contrast, the inhibition by these compounds of the NMDA-evoked current exhibited voltage-dependence and was enhanced by hyperpolarization. When the concentration of agonists was increased by 5- or 10-fold, the magnitude of the inhibition by suramin of the kainate-evoked current and the magnitude of the inhibition by RB2 of the NMDA-evoked current were attenuated. alpha,beta-Methylene ATP (100 microM) did not affect the GABA-, kainate- or NMDA-activated current. The results suggest that suramin and RB2 inhibit GABA receptor channels and glutamate receptor channels. The blockade of these channels must be taken into account when these compounds are used as pharmacological tools to examine an involvement of P2-purinoceptors, especially in preparations where GABAergic or glutamatergic neurotransmission is expected.

Evidence for the involvement of purinergic signalling in the control of respiration

“…However, this does not alter our interpretations, as we did not observe a consistent or signi¢cant augmentation of the e¡ects of ATP when suramin was microinjected into the VLM. Although non-speci¢c e¡ects of suramin have been reported in rat hippocampal neurones in culture (Nakazawa et al, 1995), suramin did not block responses to glutamate in the present study.…”

Molecular Physiology of P2X Receptors

“…The first remains the inadequacy of the antagonists available. It must be stressed that, at the concentrations used in many experiments (Ͼ30 M), suramin, PPADS, and reactive blue 2 have been shown to block currents elicited by kainate, NMDA, and GABA in dissociated cells (328) and to slow the rate of rise of currents elicited by AMPA (165). A second complication is that evoked synaptic currents are often observed in only a fraction of neurons tested, and this may make it difficult to carry out the critical comparative studies in tissues from mice in which P2X receptor subunits have been knocked out.…”

Divergent Effects of the Purinoceptor Antagonists Suramin and Pyridoxal-5′-phosphate-6-(2′-naphthylazo-6′-nitro-4′,8′-disulfonate) (PPNDS) on α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors

“…There are also reports that suramin inhibits glutamatergic synaptic transmission (Motin and Bennett, 1995;Gu et al, 1998) and whole-cell currents mediated by AMPA receptors (Nakazawa et al, 1995;Zona et al, 2000) and NMDA receptors (Ong et al, 1997;Peoples and Li, 1998). Suramin was observed to inhibit binding of radioligands to NMDA receptors (Balcar et al, 1995) but not kainate receptors (Ong et al, 1997), which suggested some selectivity among glutamate receptors.…”