Pharmacology of K+ channels in the plasmalemma of the green alga Chara corallina

Mark Tester*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

The outer membranes of plant cells contain channels which are highly selective for K+. However, many of their properties and their similarities to K+ channels found in animal cells had not previously been established. The channels open when the cells are depolarized in solutions with a high K+/Ca2+ ratio. In this work, the pharmacology of a previously identified plant K+ channel was examined. This survey showed that the channels have many properties which are similar to those of high-conductance Ca2+-activated K+ channels (high G K+(Ca2+)). K+ currents in Chara were reduced by TEA+, Na+, Cs+, Ba2+, decamethonium and quinine, all inhibitors of, among other things, high G K+(Ca2+) channels. Tetracaine also inhibited K+ currents Chara, but its effect on most types of K+ channels in animal tissues is unknown. The currents were not inhibited by 4-aminopyridine (4AP), caffeine, tolbutamide, dendrotoxin, apamin or tubocurarine, which do not inhibit high G K+(Ca2+) channels, but affect other classes of K+ channels. The channels were "locked open" by 4AP, in a remarkably similar manner to that reported for K+(Ca2+) channels of a molluscan neuron. No evidence for the role of the inositol cycle in channel behavior was found, but its role in K+ channel control in animal cells is obscure. Potassium conductance was slightly decreased upon reduction of cytoplasmic ATP levels by cyanide + salicylhydroxamic acid (SHAM), consistent with channel control by phosphorylation. The anomalously strong voltage dependence of blockade by some ions (e.g. Cs+) is consistent with the channels being multiion pores. However, the channels also demonstrate some differences from the high G K+(Ca2+) channels found in animal tissues. The venom of the scorption, Leiurus quinquestriatus (LQV), and a protein component, charybdotoxin (CTX), an apparently specific inhibitor of high G K+(Ca2+) channels in various animal tissues, had no effect on the K+ channels in the Chara plasmalemma. Als,, pinacidil, an antihypertensive drug which may increase high G K+(Ca2+) channel activity had no effect on the channels in Chara. Although the described properties of the Chara K+ channels are most similar to those of high conductance K+(Ca2+) in animal cells, the effects of CTX and pinacidil are notably different; the channels are clearly of a different structure to those found in animal cells, but are possibly related.

Original languageEnglish (US)
Pages (from-to)159-169
Number of pages11
JournalThe Journal of Membrane Biology
Volume103
Issue number2
DOIs
StatePublished - Jul 1988
Externally publishedYes

Keywords

  • 4-aminopyridine
  • apamin
  • Ca
  • charybdotoxin
  • decamethonium
  • dendrotoxin
  • inositol
  • pinacidil
  • quinine
  • tetracaine

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology

Fingerprint

Dive into the research topics of 'Pharmacology of K<sup>+</sup> channels in the plasmalemma of the green alga Chara corallina'. Together they form a unique fingerprint.

Cite this