DIFFERENTIAL EXPRESSION OF MEMBRANE CURRENTS IN DISSOCIATED MOUSE PRIMARY SENSORY NEURONS

The whole cell configuration of the patch clamp technique has been applied to identify the membrane currents expressed by populations of dissociated mouse primary sensory neurons. Three discrete populations of cells were distinguished on the basis of cell size and the array of currents expressed. Group 1 cells (capacitance 10-30 pF) expressed a Na+ current resistant to tetrodotoxin (1 mu M) and a prominent, low threshold, inactivating, K+ current sensitive to 4-aminopyridine (I-A). A population (53%) of these small cells responded to capsaicin (10 mu M) with an inward current, suggesting a functional correlate with nociceptive ''C''-cells. The cells of Group 2 (capacitance 55-85 pF) were characterized by the expression of a Na+ current sensitive to tetrodotoxin and a prominent inward current activated by hyperpolarization (I-H). They also showed a variant of the A-type K+ current, which was a low threshold, but sustained K+ current, sensitive to dendrotoxin (30 nM). Group 3 cells, of intermediate size (capacitance 30-55 pF) were similar to Group 2 cells, in that they expressed a tetrodotoxin-sensitive Na+ current and (though reduced in amplitude), I-H. The most notable feature of Group 3 cells was the expression of a transient, low threshold Ca2+ current. The differential expression of these conductances was reflected in the behaviour of cells under current clamp control. Each group of cells could thus be distinguished by the selective expression of specific ionic conductances which correlated clearly with cell size, suggesting a correlation with well recognised functional differentiation of sensory neurons. The selective expression of specific subsets of membrane channels may provide valuable markers in studying the developmental regulation of phenotype in this population of cells.