ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Delayed potassium channels were studied in internally perfused neurone somata from land snails. Relaxation and fluctuation analysis of this class of ion channels revealed Hodgkin-Huxley type K channels with an average single channel conductance (γ K) of 2.40±0.15 pS. The conductance of open channels is independent of voltage and virtually all K channels seem to be open at maximum K conductance (g K) of the membrane. Voltage dependent time constants of activation ofg K, calculated from K current relaxation and from cut-off frequencies of power spectra, are very similar indicating dominant first-order kinetics. Ion selectivity of K channels was studied by ion substitution in the external medium and exhibited the following sequence: T1+〉K+〉Rb+〉Cs+〉NH 4 + 〉Li+〉Na+. The sequence of the alkali cations does not conform to any of the sequences predicted by Eisenman's theory. However, the data are well accommodated by a new theory assuming a single rate-limiting barrier that governs ion movement through the channel.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01868997
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