Constitutively active G-protein-gated inwardly rectifying K+ channels in dendrites of hippocampal CA1 pyramidal neurons.

A diversity of ion channels contributes to the active properties of neuronal dendrites. From the apical dendrites of hippocampal CA1 pyramidal neurons, we recorded inwardly rectifying K+ channels with a single-channel conductance of 33 pS. The inwardly rectifying K+ channels were constitutively active at the resting membrane potential. The amount of constitutive channel activity was significantly larger in the apical dendrites than in the soma. Activities of these inwardly rectifying K+ channels were inhibited by Ba2+ (200 microM) and tertiapin (10 nM), both of which are believed to block G-protein-coupled inwardly rectifying K+ (GIRK) channels. Intracellularly applied GTPgammaS (20 microM) during dual dendritic recordings significantly increased constitutive channel activity. Baclofen (20 microM), an agonist for the G-protein-coupled GABA(B) receptor, also significantly increased the level of channel activity. Therefore, these channels are GIRK channels, which are constitutively active at rest in the apical dendrites of CA1 pyramidal neurons and can be further activated via G-protein-coupled neurotransmitter receptors.