CHANGES IN POTASSIUM CHANNEL ACTIVITY FOLLOWING AXOTOMY OF B-CELLS IN BULLFROG SYMPATHETIC-GANGLION

1. Whole-cell and microelectrode voltage-clamp techniques were used to investigate the changes in ionic currents and action potential shape that follow axotomy of bullfrog paravertebral sympathetic ganglion B-cells. 2. Axotomy increased M-conductance (g(M); muscarine-sensitive, voltage- and time-dependent K+ conductance) by 35% at -30 mV and slowed its deactivation kinetics. 3. The delayed rectifier K+ current (I-K; at +50 mV) was reduced in axotomized neurones to 61% of control without any change in activation or deactivation kinetics. Steady-state intracellular Ca2+ levels and leak conductance were unchanged. 4. The fast, voltage-sensitive, Ca2+-activated K+ current (I-C), evoked from -40 mV, was decreased to about 71% of control (at +30 mV) in axotomized neurones, whereas that evoked from -80 mV was largely unaffected. I-C kinetics were also similar in control and axotomized neurones. This suggests that I-C channels are not changed after axotomy. 5. In axotomized neurones, commands to +10 from -40 mV had to be extended by 16 ms to evoke voltage-insensitive Ca2+-dependent K+ current (I-AHP) responses that were similar in magnitude to those observed in control cells. 6. The previously documented, axotomy-induced decrease in Ca2+ current (I-Ca) due to increased resting inactivation can account for the reduction in I-C and I-AHP and for the change in the shape of the action potential.