Induction of endogenous channels by high levels of heterologous membrane proteins in Xenopus oocytes

Biophys J. 1995 Sep;69(3):904-8. doi: 10.1016/S0006-3495(95)79964-7.

Abstract

Xenopus oocytes are widely employed for heterologous expression of cloned proteins, particularly electrogenic molecules such as ion channels and transporters. The high levels of expression readily obtained permit detailed investigations without interference from endogenous conductances. Injection of min K mRNA into Xenopus oocytes results in expression of voltage-dependent potassium-selective channels. Recent data show that injections of high concentrations of min K mRNA also induce a chloride current with very different biophysical, pharmacological, and regulatory properties from the min K potassium current. This led to the suggestion that the min K protein acts as an inducer of endogenous, normally silent oocyte ion channels. We now report that high levels of heterologous expression of many membrane proteins in Xenopus oocytes specifically induce this chloride current and a hyperpolarization-activated cation-selective current. The current is blocked by 4,4'-diisothiocyanostilbene-2-2'-disulphonic acid and tetraethylammonium, enhanced by clofilium, and is pH-sensitive. Criteria are presented that distinguish this endogenous current from those due to heterologous expression of electrogenic proteins in Xenopus oocytes. Together with structure-function studies, these results support the hypothesis that the min K protein comprises a potassium-selective channel.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / analogs & derivatives
  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / pharmacology
  • Animals
  • Calcium / pharmacology
  • Chloride Channels / antagonists & inhibitors
  • Chloride Channels / biosynthesis
  • Chloride Channels / physiology*
  • Cloning, Molecular
  • Cross-Linking Reagents / pharmacology
  • Female
  • Gene Expression
  • Membrane Potentials
  • Membrane Proteins / biosynthesis*
  • Oocytes / physiology*
  • Potassium Channels / biosynthesis
  • Potassium Channels / physiology*
  • Recombinant Proteins / biosynthesis
  • Xenopus

Substances

  • Chloride Channels
  • Cross-Linking Reagents
  • Membrane Proteins
  • Potassium Channels
  • Recombinant Proteins
  • dihydro-DIDS
  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid
  • Calcium