INWARD RECTIFIER POTASSIUM CURRENT IN DOPAMINERGIC NEURONES OF MOUSE OLFACTORY BULB

Inwardly rectifying potassium (Kir) channels are important for neuronal signalling and membrane excitability. In the present work, we used patch-clamp techniques to characterize Kir channels in mouse dopaminergic (DA) periglomerular (PG) cells, interneurons located at the entry of the bulbar circuitry whose role is not yet well defined. Perforated-patch configuration was adopted to record the current mediated by Kir channels in DA-PG cells in thin slice; IKir could be distinguished from the hyperpolarization-activated current (Ih) by showing full activation in < 10 ms, no inactivation, suppression by Ba2+ in a typical voltage-dependent manner (IC50 208 µM) and reversal potential nearly coincident with EK. The Ba2+ blockage of IKir depolarizes the cell enough to block the spontaneous activity, although the Kir current is not an essential component of the pacemaker machinery; furthermore, Ba2+ (2 mM) also induces a significant increase in input resistance . The current is negatively modulated by intracellular cAMP, as shown by a 16% decrease of its amplitude induced by forskolin (10 µM). We have also tested the neuromodulatory effects of the activation of several metabotropic receptors which are known to be present on these cells, showing that the current can be modulated in both directions by a multiplicity of pathways, whose activation in some case increase the amplitude of the current, as it can be observed with agonists of muscarinic, α1 noradrenergic and GABAA receptors, whereas in other case have the opposite effect, as it can be observed with agonists of D2, 5-HT and histamine receptors.