RESUMEN
Small-conductance Ca(2+)-activated K(+) (KCa2) channels control neuronal excitability and synaptic plasticity, and have been implicated in substance abuse. However, it is unknown if genes that encode KCa2 channels (KCNN1-3) influence alcohol and drug addiction. In the present study, an integrative functional genomics approach shows that genetic datasets for alcohol, nicotine, and illicit drugs contain the family of KCNN genes. Alcohol preference and dependence QTLs contain KCNN2 and KCNN3, and Kcnn3 transcript levels in the nucleus accumbens (NAc) of genetically diverse BXD strains of mice predicted voluntary alcohol consumption. Transcript levels of Kcnn3 in the NAc negatively correlated with alcohol intake levels in BXD strains, and alcohol dependence enhanced the strength of this association. Microinjections of the KCa2 channel inhibitor apamin into the NAc increased alcohol intake in control C57BL/6J mice, while spontaneous seizures developed in alcohol-dependent mice following apamin injection. Consistent with this finding, alcohol dependence enhanced the intrinsic excitability of medium spiny neurons in the NAc core and reduced the function and protein expression of KCa2 channels in the NAc. Altogether, these data implicate the family of KCNN genes in alcohol, nicotine, and drug addiction, and identify KCNN3 as a mediator of voluntary and excessive alcohol consumption. KCa2.3 channels represent a promising novel target in the pharmacogenetic treatment of alcohol and drug addiction.
Asunto(s)
Alcoholismo/genética , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/genética , Trastornos Relacionados con Sustancias/genética , Alcoholismo/etiología , Análisis de Varianza , Animales , Apamina/toxicidad , Depresores del Sistema Nervioso Central/toxicidad , Conducta de Elección/efectos de los fármacos , Biología Computacional , Condicionamiento Operante/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Etanol/administración & dosificación , Femenino , Humanos , Técnicas In Vitro , Modelos Lineales , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Análisis por Micromatrices/estadística & datos numéricos , Microinyecciones , Núcleo Accumbens/citología , Núcleo Accumbens/efectos de los fármacos , Técnicas de Placa-Clamp , Bloqueadores de los Canales de Potasio/toxicidad , Sitios de Carácter Cuantitativo , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/clasificación , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Transmisión Sináptica/efectos de los fármacos , Transmisión Sináptica/genéticaRESUMEN
The effects of low intracellular pH (pH(i) 6.4) on cloned small-conductance Ca2+-activated K+ channel currents of all three subtypes (SK1, SK2, and SK3) were investigated in HEK293 cells using the patch-clamp technique. In 400 nM internal Ca2+ [Ca2+]i, all subtypes were inhibited by pH(i) 6.4 in the order of sensitivity: SK1>SK3>SK2. The inhibition increased with the transmembrane voltage. In saturating internal Ca2+, the inhibition was abolished for SK1-3 channels at negative potentials, indicating a [Ca2+]i-dependent mode of inhibition. Application of 50 microM 1-ethyl-2-benzimidazolone was able to potentiate SK3 current to the same extent as at neutral pH(i). We conclude that SK1-3 all are inhibited by low pH(i). We suggest two components of inhibition: a [Ca2+]i-dependent component, likely involving the SK beta-subunits calmodulin, and a voltage-dependent component, consistent with a pore-blocking effect. This pH(i)-dependent inhibition can be reversed pharmacologically.