Functional Na+/K+ pump in rat dorsal root ganglia neurons

Steady-state Na+/K+ pump current (I-p) in isolated adult rat dorsal root ganglia neurons was studied to determine if the plasma membrane Na+/K+ pump activity is uniform across the population of dorsal root ganglia neurons. Cells were voltage-clamped at -40 mV and holding current (I-h) was recorded using whole-cell patch-clamp techniques under conditions that stimulate the Na+/K+ pump (60 mM intracellular Na+ and 5.4 mM extracellular K+). I-p was defined as the 1 mM ouabain-sensitive fraction of I-h Data suggest the existence of three subpopulations of dorsal root ganglia neurons having mean steady-state I-p densities of 1.6 +/- 0.1, 3.8 +/- 0.2 and 7.5 +/- 0.4 pA/pF. Neurons with small I-p had an average soma perimeter of 95 +/- 3 mu m, while neurons with medium and large I-p density had significantly larger soma sizes (131 +/- 8 and 141 +/- 7 mu m, respectively). Neurons with a large I-p density had a significantly lower specific membrane resistance (R-m; mean 4.0 +/- 0.3 k Omega.cm(2)) than neurons with medium or small I-p density (19 +/- 6 and 31 +/- 6 k Omega.cm(2), respectively). Regardless of these differences, in all groups of neurons I-p had a low sensitivity to ouabain (I-p half inhibition by ouabain was observed at 80-110 mu M). These data suggest that the Na+/K+ pump site density and/or its activity is not uniform throughout the dorsal root ganglia neuron population; however, this non-uniformity does not appear to relate to the functional expression of the different alpha isoforms of the Na+/K+ pump. The major functional Na+/K+ pump in the dorsal root ganglia neuron plasma membrane appeared to be the low ouabain affinity (alpha(1)) isoform. (C) 1999 IBRO. Published by Elsevier Science Ltd.