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.
Department of Pharmacology, University of Alberta, Edmonton, Canada.
B S
BS
Jassar
P S
PS
Pennefather
P A
PA
Smith
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