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 (gM; muscarine-sensitive, voltage- and time-dependent K+ conductance) by 35% at -30 mV and slowed its deactivation kinetics. 3. The delayed rectifier K+ current (IK; 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, Ca(2+)-activated K+ current (IC), 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. IC kinetics were also similar in control and axotomized neurones. This suggests that IC 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 Ca(2+)-dependent K+ current (IAHP) responses that were similar in magnitude to those observed in control cells. 6. The previously documented, axotomy-induced decrease in Ca2+ current (ICa) due to increased resting inactivation can account for the reduction in IC and IAHP and for the change in the shape of the action potential.
Jassar
B S
BS
Department of Pharmacology, University of Alberta, Edmonton, Canada.
Pennefather
P S
PS
Smith
P A
PA
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001369:Axons / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000378:metabolism*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D008839:Microelectrodes; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D011892:Rana catesbeiana; D011976:Receptors, Muscarinic / Q000378:metabolism
D015221:Potassium Channels; D011976:Receptors, Muscarinic; D002118:Calcium