Modulation by K+ Channels of Action Potential-Evoked Intracellular Ca2+ Concentration Rises in Rat Cerebellar Basket Cell Axons

J Physiol. 1999 Oct 1;520 Pt 1(Pt 1):65-78. doi: 10.1111/j.1469-7793.1999.00065.x.

Abstract

1. Action potential-evoked [Ca2+]i rises in basket cell axons of rat cerebellar slices were studied using two-photon laser scanning microscopy and whole-cell recording, to identify the K+ channels controlling the shape of the axonal action potential. 2. Whole-cell recordings of Purkinje cell IPSCs were used to screen K+ channel subtypes which could contribute to axonal repolarization. alpha-Dendrotoxin, 4-aminopyridine, charybdotoxin and tetraethylammonium chloride increased IPSC rate and/or amplitude, whereas iberiotoxin and apamin failed to affect the IPSCs. 3. The effects of those K+ channel blockers that enhanced transmitter release on the [Ca2+]i rises elicited in basket cell axons by action potentials fell into three groups: 4-aminopyridine strongly increased action potential-evoked [Ca2+]i; tetraethylammonium and charybdotoxin were ineffective alone but augmented the effects of 4-aminopyridine; alpha-dendrotoxin had no effect. 4. We conclude that cerebellar basket cells contain at least three pharmacologically distinct K+ channels, which regulate transmitter release through different mechanisms. 4-Aminopyridine-sensitive, alpha-dendrotoxin-insensitive K+ channels are mainly responsible for repolarization in basket cell presynaptic terminals. K+ channels blocked by charybdotoxin and tetraethylammonium have a minor role in repolarization. alpha-Dendrotoxin-sensitive channels are not involved in shaping the axonal action potential waveform. The two last types of channels must therefore exert control of synaptic activity through a pathway unrelated to axonal action potential broadening.

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Animals
  • Axons / metabolism*
  • Axons / ultrastructure
  • Calcium / metabolism*
  • Cerebellum / cytology
  • Cerebellum / metabolism*
  • Cerebellum / ultrastructure
  • Elapid Venoms / pharmacology
  • Electrophysiology
  • Excitatory Postsynaptic Potentials / drug effects
  • Excitatory Postsynaptic Potentials / physiology
  • In Vitro Techniques
  • Neurotoxins / pharmacology
  • Patch-Clamp Techniques
  • Potassium Channel Blockers
  • Potassium Channels / physiology*
  • Presynaptic Terminals / drug effects
  • Presynaptic Terminals / physiology
  • Purkinje Cells / drug effects
  • Purkinje Cells / physiology
  • Rats

Substances

  • Elapid Venoms
  • Neurotoxins
  • Potassium Channel Blockers
  • Potassium Channels
  • dendrotoxin
  • 4-Aminopyridine
  • Calcium