Evidence for the involvement of Na +-K + pump and K + conductance in the post-tetanic hyperpolarization of the tetrodotoxin-resistant C-fibers in the isolated bullfrog sciatic nerve

Abstract

The post-tetanic hyperpolarizations (PTHPs) were recorded from the isolated bullfrog sciatic nerves using a modified vaseline gap method. Repetitive stimulation of tetrodotoxin-resistant (TTX-R) C-fibers produced frequency- and activity-dependent PTHPs. The ouabain solutions (0.1 mM), the solutions (0.1 mM ouabain+2 mM tetraethylammonium (TEA)) and 5 mM TEA solutions reduced the PTHP amplitude to 56.2±10.7% (mean±SD, n=9), to 37.0±12.3% ( n=8), to 76.0±10.9% ( n=5) of the control value, respectively. Each pair of the three solutions revealed a significant difference in their effects on the PTHP ( P<0.01). Furthermore, the Li–Ringer solutions and the solutions (Li–Ringer+2 mM TEA) reduced the PTHP amplitude as well, thus resembling ouabain effects. These results strongly suggest that the repetitive stimulation of TTX-R C-fibers activates the membrane Na +-K + pump resulting in a major part of the PTHP and induces TEA-sensitive K + conductance composing a minor part of the PTHP, which might modulate repetitive firing of TTX-R C-fibers.