Inward rectifier potassium current in dopaminergic periglomerular cells of mouse olfactory bulb.

Inward rectifier potassium (Kir) channels are important for neuronal signalling and membrane excitability. In this work, patch-clamp techniques were used to characterize Kir channels in mouse dopaminergic (DA) periglomerular (PG) cells. These interneurons are critically placed at the entry of the bulbar circuitry, in contact with terminals of olfactory sensory neurons and with dendrites of projection neurons. Perforated-patch configuration was adopted to record Kir current in DA-PG cells in thin slice. IKir could be distinguished from the hyperpolarization-activated current by showing full activation in < 10 ms, no inactivation, suppression by Ba2+ in a typical voltage-dependent manner and reversal potential nearly coincident with EK. DA-PG cells are autorhythmic and are target of numerous afferents releasing a variety of neurotransmitters, although their properties and role remain elusive. Depolarization induced by Ba2+ blocks spontaneous activity, although the Kir current is not an essential component of the pacemaker machinery. The current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin. Several neuromodulatory effects were tested on the Kir current of DA-PG cell. Activation of metabotropic receptors - known to be present on these cells - shows that the current can be modulated by a multiplicity of pathways. The Kir current can be increased, as observed with agonists of muscarinic, α1 noradrenergic and GABAA receptors, or IKir modulation can caused the opposite effect, i.e. agonists of D2, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for additional flexibility of DA-PG cells signaling and function.