Phosphorylation and dephosphorylation modulate a Ca(2+)-activated K+ channel in rat peptidergic nerve terminals

J Physiol. 1994 Mar 1;475(2):241-54. doi: 10.1113/jphysiol.1994.sp020065.

Abstract

1. Ca(2+)-activated K+ channels regulate the excitability of many nerve terminals. A Ca(2+)-activated K+ channel present in the membranes of rat posterior pituitary nerve terminals runs down following the formation of excised patches. This run-down process reflects enzymatic dephosphorylation. 2. Both Mg-ATP and the protein phosphatase inhibitor okadaic acid prevented run-down of channel activity in excised patches. The okadaic acid sensitivity suggests that run-down resulted from dephosphorylation by a type 1 protein phosphatase. 3. Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) accelerated run-down by accelerating okadaic acid-sensitive dephosphorylation. GTP gamma S had no effect on the activity of the protein kinase in these patches. These results suggest a direct coupling between a G-protein and a protein phosphatase. 4. After run-down, channel activity could be restored by Mg-ATP; restoration depended on ATP hydrolysis, but did not require Ca2+ or a second messenger. Restoration of channel activity by ATP was blocked by staurosporine and 1-(5-isoquinolinylsulphonyl)-3-methylpiperizine, but not by more specific inhibitors of protein kinases. 5. Restoration of channel activity by phosphorylation was very sensitive to membrane potential; increasing the voltage by as little as 10 mV could dramatically enhance recovery. 6. Ca2+ and voltage acted synergistically to enhance phosphorylation; higher [Ca2+] permitted phosphorylation at more negative potentials. 7. During trains of high frequency stimulation under current clamp, action potentials were influenced by both the protein phosphatase and protein kinase, indicating that enzymatic modulation of channel gating occurs under physiological conditions. An important implication of these results is that voltage-dependent phosphorylation could play a role in use-dependent depression of secretion from nerve terminals.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Action Potentials
  • Adenosine Triphosphate / metabolism
  • Adenosine Triphosphate / pharmacology
  • Animals
  • Brain / metabolism
  • Calcium / metabolism*
  • Enzyme Activation
  • Ethers, Cyclic / pharmacology
  • GTP-Binding Proteins / metabolism
  • Guanosine 5'-O-(3-Thiotriphosphate) / pharmacology
  • In Vitro Techniques
  • Membrane Potentials
  • Nerve Endings / drug effects
  • Nerve Endings / metabolism*
  • Okadaic Acid
  • Phosphoprotein Phosphatases / antagonists & inhibitors
  • Phosphoprotein Phosphatases / metabolism
  • Phosphorylation
  • Pituitary Gland, Posterior / drug effects
  • Pituitary Gland, Posterior / metabolism
  • Potassium Channels / metabolism*
  • Protein Kinase Inhibitors
  • Protein Kinases / metabolism
  • Rats

Substances

  • Ethers, Cyclic
  • Potassium Channels
  • Protein Kinase Inhibitors
  • Okadaic Acid
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Adenosine Triphosphate
  • Protein Kinases
  • Phosphoprotein Phosphatases
  • GTP-Binding Proteins
  • Calcium