A patch-clamp analysis of membrane currents in salamander olfactory receptor cells

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Abstract
Isolated olfactory receptor cells were obtained from salamander olfactory epithelium and kept in short term culture conditions. They were studied by means of the whole cell patch-clamp technique associated with ionic substitutions and channel blockers. Under physiological ionic gradients, these cells had a resting potential of −39±10 mV and an input resistance above 2 GΩ. Using different channel blockers and ion substitutions, we could separate several distinct components in the overall whole cell current. In most cells, inward current reflected the activation of a TTX resistant conductance which was blocked by cobalt ions. This inward current lasted only for about 5 min of whole cell recording. In a minority of cells, a TTX sensitive sodium current was also observed. The outward K+ current was blocked when the cells were loaded with cesium and tetraethylammonium. It inactivated slowly and incompletely and could act as a depolarization limiter in case of intense odour stimulations. Single channel analysis from outside out patches suggested that it corresponded to the activity of 34 pS channels. In some cells a rapidly inactivating K+ current was also present. Single channel activities (27±6 pS) were commonly recorded with KCl-filled pipettes, at resting or hyperpolarized membrane potentials but not at depolarized potentials. Membrane hyperpolarization increased the open-state probability. A preliminary study with odorant stimulations indicated the existence of a stimulus-induced current probably corresponding to the activation of the chemoreceptive membrane.