Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes

Zheng Fan, Tetsushi Furukawa, Tohru Sawanobori, Jonathan C. Makielski, Masayasu Hiraoka

Research output: Contribution to journalArticle

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Abstract

We studied the effect of cytoplasmic acidosis on the ionic conducting states of ATP-sensitive potassium channels in heart ventricular cells of guinea pigs and rabbits by using a patch-clamp technique with inside-out patch configuration. Under normal conditions (pH 7.4), the channel alternated between a closed state and a main open state in the absence of nucleotides on the cytoplasmic side. As internal pH was reduced below 6.5, the single channel current manifested distinct subconductance levels. The probability of the appearance of these subconductance levels was pH dependent with a greater probability of subconductance states at lower pH. A variance-mean amplitude analysis technique revealed two subconductance levels approximately equally spaced between the main open level and the closed level (63 and 33%). A current-voltage plot of the two subconductance levels and the main level showed that they had similar reversal potentials and rectification properties. An intrinsic flickering gating property characteristic of these ATP-sensitive channels was found unchanged in the 63% subconductance state, suggesting that this subconductance state and the main conductance state share similar ion pore properties (including ion selection and block) and similar gating mechanisms. The appearance of the subconductance states decreased as ionic strength was increased, and the subconductance states were also slightly voltage dependent, suggesting an electrostatic interaction between the protons and the negative surface charge in the vicinity of the binding sites, which may be close to the inner entrance of the ion pore. Proteolytic modification of the channel on the cytoplasmic side with trypsin did not abolish the subconductance levels. External acidosis did not induce subconductance levels. These results suggest that protons bound to the negatively charged group at the inner entrance of the channel ion pore may induce conformational changes, leading to partially reduced conductance states.

Original languageEnglish (US)
Pages (from-to)169-179
Number of pages11
JournalThe Journal of Membrane Biology
Volume136
Issue number2
DOIs
StatePublished - Nov 1 1993
Externally publishedYes

Fingerprint

KATP Channels
Acidosis
Cardiac Myocytes
Ions
Protons
Patch-Clamp Techniques
Static Electricity
Ion Channels
Osmolar Concentration
Trypsin
Guinea Pigs
Nucleotides
Adenosine Triphosphate
Binding Sites
Rabbits

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Physiology
  • Cell Biology

Cite this

Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes. / Fan, Zheng; Furukawa, Tetsushi; Sawanobori, Tohru; Makielski, Jonathan C.; Hiraoka, Masayasu.

In: The Journal of Membrane Biology, Vol. 136, No. 2, 01.11.1993, p. 169-179.

Research output: Contribution to journalArticle

Fan, Zheng ; Furukawa, Tetsushi ; Sawanobori, Tohru ; Makielski, Jonathan C. ; Hiraoka, Masayasu. / Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes. In: The Journal of Membrane Biology. 1993 ; Vol. 136, No. 2. pp. 169-179.
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