Properties of the Na + /K + pump current in small neurons from adult rat dorsal root ganglia

The present investigation was undertaken to characterize the Na + /K + pump current in small (25 μ m in soma diameter) dorsal root ganglion (DRG) neurons isolated from lumbar L4‐6 segments of adult rats. The Na + /K + pump current was identified as an ouabain‐sensitive current during square voltage steps to membrane potentials between +40 and −120 mV, using the whole‐cell patch‐clamp technique in which Ca 2+ and K + channel currents and Na + /Ca 2+ exchange currents were minimized. The Na + /K + pump current was practically time‐independent over the entire voltage range examined and exhibited a voltage‐dependence; its current – voltage ( I–V ) relationship displayed a positive slope at potentials between −120 and 0 mV but nearly plateau levels at positive membrane potentials. The concentration‐dependent block of Na + /K + pump current (activated by 30 m M pipette Na + ) by ouabain at concentrations between 0.1 μ M and 5 m M was biphasic and was well described using a two‐binding site model with dissociation constants for high‐ and low‐affinity binding sites of 0.20 and 140.1 μ M , respectively. The relative amplitude of the Na + /K + pump current produced by low‐ and high‐affinity sites (probably α 1 β 1 and α 3 β 1 isozymes, respectively) was estimated to be 13 : 1 in the presence of 30 m M Na + in the pipette solution. Additionally, the activation of Na + /K + pump current by pipette Na + at concentrations ranging from 5 to 100 m M also exhibited a biphasic concentration dependence which can be reasonably well fitted by assuming the existence of two isozymes having high and low affinities for Na + (6.7 and 67.6 m M , respectively). Thus, the present investigation provides functional evidence to suggest that the Na + /K + ATPase comprises two functionally distinct isozymes as expected for α 1 β 1 and α 3 β 1 in rat small DRG neurons.British Journal of Pharmacology (2003) 138 , 1517–1527. doi: 10.1038/sj.bjp.0705170