INWARD RECTIFIER POTASSIUM CURRENT IN DOPAMINERGIC CELLS OF THE MOUSE OLFACTORY BULB

Dopaminergic (DA) periglomerular (PG) cells are autorhythmic interneurons strategically located at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons. In these cells, we have kinetically and functionally characterized the inward rectifier potassium (Kir) current. Perforated-patch configuration was adopted to record the Kir current in DA-PG cells in thin slices. IKir could be distinguished from another hyperpolarization-activated current, Ih, by showing full activation in < 10 ms, no inactivation, voltage-dependent suppression by Ba2+ and reversal potential coincident with EK. Ba2+ blockage produces an increase of the input resistance and a large depolarization of DA-PG cells, leading to a block of the spontaneous activity. However, the Kir current is not essential for the pacemaker machinery but controls the resting potential. The Kir current is inhibited by intracellular cAMP, as shown by the effects of forskolin and of 8-Br-cAMP. We have also tested the neuromodulatory effects of several neurotransmitters known to be released onto these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current (agonists of muscarinic, agonists of D2 and GABAA receptors), whereas in other cases has the opposite effect (agonists of a1 noradrenergic, 5-HT and histamine receptors). These characteristics of the Kir current provide the basis for an unexpected plasticity of DA-PG cells function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.