Anti-NPPB monoclonal antibody, clone 29G9

GABAergic inhibition in the central nervous system (CNS) can occur via rapid, transient postsynaptic currents and via a tonic increase in membrane conductance, mediated by synaptic and extrasynaptic GABA(A) receptors (GABA(A)Rs) respectively. Retinal bipolar cells (BCs) exhibit a tonic current mediated by GABA(C)Rs in their axon terminal, in addition to synaptic GABA(A)R and GABA(C)R currents, which strongly regulate BC output. The tonic GABA(C)R current in BC terminals (BCTs) is not dependent on vesicular GABA release, but properties such as the alternative source of GABA and the identity of the GABA(C)Rs remain unknown. Following a recent report that tonic GABA release from cerebellar glial cells is mediated by Bestrophin 1 anion channels, we have investigated their role in non-vesicular GABA release in the retina. Using patch-clamp recordings from BCTs in goldfish retinal slices, we find that the tonic GABA(C)R current is not reduced by the anion channel inhibitors NPPB or flufenamic acid but is reduced by DIDS, which decreases the tonic current without directly affecting GABA(C)Rs. All three drugs also exhibit non-specific effects including inhibition of GABA transporters. GABA(C)R rho subunits can form homomeric and heteromeric receptors that differ in their properties, but BC GABA(C)Rs are thought to be rho 1-rho 2 heteromers. To investigate whether GABA(C)Rs mediating tonic and synaptic currents may differ in their subunit composition, as is the case for GABA(A)Rs, we have examined the effects of two antagonists that show partial rho subunit selectivity: picrotoxin and cyclothiazide. Tonic and synaptic GABA(C)R currents were differentially affected by both drugs, suggesting that a population of homomeric rho 1 receptors contributes to the tonic current. These results extend our understanding of the multiple forms of GABAergic inhibition that exist in the CNS and contribute to visual signal processing in the retina.

Wang L, Ma W, Zhu L, Ye D, Li Y, Liu S, Li H, Zuo W, Li B, Ye W, Chen L. ClC-3 is a candidate of the channel proteins mediating acid-activated chloride currents in nasopharyngeal carcinoma cells. Am J Physiol Cell Physiol 303: C14-C23, 2012. First published April 11, 2012; doi:10.1152/ajpcell.00145.2011.-Acid-activated chloride currents have been reported in several cell types and may play important roles in regulation of cell function. However, the molecular identities of the channels that mediate the currents are not defined. In this study, activation of the acid-induced chloride current and the possible candidates of the acid-activated chloride channel were investigated in human nasopharyngeal carcinoma cells (CNE-2Z). A chloride current was activated when extracellular pH was reduced to 6.6 from 7.4. However, a further decrease of extracellular pH to 5.8 inhibited the current. The current was weakly outward-rectified and was suppressed by hypertonicity-induced cell shrinkage and by the chloride channel blockers 5-nitro-2-3-phenylpropylamino benzoic acid (NPPB), tamoxifen, and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt hydrate (DIDS). The permeability sequence of the channel to anions was I- > Br- > Cl- > gluconate(-). Among the ClC chloride channels, ClC-3 and ClC-7 were strongly expressed in CNE-2Z cells. Knockdown of ClC-3 expression with ClC-3 small interfering (si) RNA prevented the activation of the acid-induced current, but silence of ClC-7 expression with ClC-7 siRNA did not significantly affect the current. The results suggest that the chloride channel mediating the acid-induced chloride current was volume sensitive. ClC-3 is a candidate of the channel proteins that mediate or regulate the acid-activated chloride current in nasopharyngeal carcinoma cells.