Increased Alcohol Consumption in Mice Lacking Sodium Bicarbonate Transporter NBCn1

Abstract

christian Aalkjaer 5 , ebbe Boedtkjer 5 & inyeong choi 2 ✉ The previous reports on an addiction vulnerability marker in the human SLC4A7 gene encoding the na/Hco 3 transporter NBCn1 suggest that this pH-regulating protein may affect alcohol-related behavior and response. Here, we examined alcohol consumption and sensitivity to the sedative effects of alcohol in male NBCn1 knockout mice. These mice displayed lower pH in neurons than wildtype controls, determined by intracellular pH in hippocampal neuronal cultures. neurons from knockout mice had a higher action potential threshold and a more depolarized membrane potential, thus reducing membrane excitability. in a two-bottle free choice procedure, knockout mice consumed more alcohol than controls and consistently increased alcohol consumption after repeated alcohol deprivation periods. Quinine and sucrose preference was similar between genotypes. Knockout mice showed increased propensity for alcohol-induced conditioned place preference. In loss of righting reflex assessment, knockout mice revealed increased sensitivity to alcohol-induced sedation and developed tolerance to the sedation after repeated alcohol administrations. furthermore, chronic alcohol consumption caused NBCn1 downregulation in the hippocampus and striatum of mice and humans. These results demonstrate an important role of NBCn1 in regulation of alcohol consumption and sensitivity to alcohol-induced sedation. pH is a broad but important biological factor that can cause significant changes in brain function 1,2. pH can change activities of numerous proteins such as neurotransmitter receptors, ion channels, and synaptic transmission machinery proteins, and such changes perturb membrane excitability, firing properties, and intracellular signaling cascades 3,4. The physiological importance of pH in neurons has been documented 5,6 ; nonetheless, it is presently unclear whether pH affects reward, motivation and addiction. In the field of addiction research, pH disturbance has been viewed as the consequence of drug action or metabolism 7. For example, the risk of metabolic acidosis is increased by an overdose of drugs including cocaine, heroin, and ecstasy 8. Metabolic acidosis is also induced by chronic or heavy alcohol consumption 9,10. This metabolic complication is due to the conversion of alcohol to ketone bodies such as β-hydroxybutyrate, thus consuming HCO 3 −. For example, a study shows that about 25% of alcoholic admissions in hospitals have ketogenic acidosis 11 , which affects many organ functions. Nonetheless, little is known whether pH conversely affects drug consumption or drug-induced response. NBCn1 (SLC4A7) is a pH-regulating plasma membrane protein found in a variety of tissues 12. In most neurons, NBCn1 is predominantly localized to postsynaptic membranes 13 , where it transports Na + and HCO 3 − into neurons and buffers intracellular H +. Thus, the transporter regulates intracellular pH (pH i) in postsynaptic neurons and extracellular pH (pH o) in the synaptic cleft. Genome-wide assoc...

Decreased Brain pH and Pathophysiology in Schizophrenia

“…Knockouts of these neuronal NCBTs protect mice from seizures incidence and mortality in response to pentylenetetrazol, pilocarpine, or NMDA [14,20,22]. Among neuronal NCBTs, NBCn1 and NDCBE affect glutamate neurotransmission [20][21][22]149] and thus are of particular interest with respect to their potential involvement in schizophrenia. NBCn1 interacts with the NMDA receptor subunit GluN1 and constitutes a protein complex in the postsynaptic density [20,151].…”

“…This inhibition protects neurons from NMDA-mediated excitotoxicity [13]. Furthermore, mice with genetic deletion of some NCBTs such as NBCn1, NCBE, and NDCBE develop less excitable membranes, higher resting potential, or decreased glutamate release [20][21][22], and they are less susceptible to repetitive discharges in response to pentylenetetrazol, pilocarpine or NMDA [20,22]. Taken together, it is conceivable that the lowered brain pH in schizophrenia patients will influence synaptic activities involved in the pathophysiology of schizophrenia.…”

Antibodies toward Na+,HCO3–-cotransporter NBCn1/SLC4A7 block net acid extrusion and cause pH-dependent growth inhibition and apoptosis in breast cancer

“…Although NBCn1 has a broad expression profile in normal tissue [ 28 ], most non-cancerous cells experience a near-normal pH o and a moderate metabolic acid load that they can adequately eliminate even if NBCn1 is inhibited. Accordingly, global constitutive NBCn1 knockout mice show only modest phenotypes until they are challenged, for instance, by aging, augmented acid-loading, substance abuse, carcinogen treatment, or infusion with vasoactive agonists [ 28 – 33 ]. The multiple splice variants of SLC4A7 , with distinct tissue-specific expression profiles [ 34 , 35 ], may permit predominant targeting of NBCn1 in disease-affected tissue.…”

Sodium Bicarbonate Decreases Alcohol Consumption in Mice

“…We previously reported that alcohol consumption is high in mice with targeted inactivation of a pH-regulating protein found in many cells, including neurons [21]. These mice have low pH in neurons and display increased responses to alcohol due to the development of increased motivation to drink alcohol.…”