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The decline of potassium permeability during extreme hyperpolarization in frog skeletal muscle
Author(s) -
Almers W.
Publication year - 1972
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1972.sp009929
Subject(s) - hyperpolarization (physics) , conductance , chemistry , membrane potential , time constant , permeability (electromagnetism) , potassium , biophysics , reversal potential , membrane permeability , voltage clamp , analytical chemistry (journal) , membrane , patch clamp , physics , chromatography , biology , biochemistry , condensed matter physics , stereochemistry , electrical engineering , engineering , organic chemistry , nuclear magnetic resonance spectroscopy , receptor
1. The voltage‐clamp technique was used to separate the effects of K depletion in the T‐system from the decline in K permeability during hyperpolarization, and to characterize the time‐ and voltage‐dependence of the latter. 2. K permeability due to the inward rectifier can be described as being proportional to a parameter which diminishes when the membrane is hyperpolarized beyond −120 mV. The parameter obeys first‐order kinetics. At 24° C, it can change with a time constant of 49 msec at −150 mV and 25 msec at −65 mV. At −200 mV the fall in membrane conductance due to the permeability change is to 30% of its initial value. The Q 10 for the rate of conductance change at that potential is about 2·8. 3. It is estimated that K inward current can lower the average K concentration in the T‐system by more than 50%, and that, on the average, the space enclosed by the T‐system should be less than 0·8% of the fibre volume. Assuming the T‐system space to be 0·3% of the fibre volume, it is calculated that on the average, and during hyperpolarization to about −150 mV, no more than 20% of the initial current should flow across the surface membrane.