Tetrodotoxin-resistant sodium and calcium components of action potentials in dorsal root ganglion cells of the adult mouse.

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Abstract
The ionic requirements and the tetrodotoxin (TTX) sensitivity of the action potential of dorsal root ganglion (DRG) cells dissected from an adult mouse were studied with intracellular microelectrodes. The DRG cells were classified into 3 groups as below (3-5) according to the 2 physiological properties: capability of producing a Ca-dependent regenerative response in Na-free solution and TTX sensitivity of the spike in normal solution. The neurons generating a TTX-resistant (10-6 g/ml) spike with Na and Ca components are named H-neurons because of showing a hump on the falling phase of the action potential. Only 5% of the cells studied belong to this group. The neurons eliciting a TTX-resistant Na spike are named A-neurons for displaying a large and long-lasting after hyperpolarization. The neurons of this type amount to 27% of the cells examined. The neurons producing a TTX-sensitive (10-8 g/ml) Na spike are named F-neurons for the fast time course of the spike. Most cells (68%) were of this type. Time-dependent inward-going rectification (anomalous rectification) was observed both in F- and A-neurons. F-neurons showed a stronger rectification than A-neurons. A decrease of active Ca channels and an increase of the TTX sensitivity of Na channels may occur in the developmental course of the DRG cells.