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Some properties of the external activation site of the sodium pump in crab nerve
Author(s) -
Baker P. F.,
Connelly C. M.
Publication year - 1966
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.1966.sp007987
Subject(s) - ouabain , sodium , potassium , chemistry , ion , oxygen , biophysics , organic chemistry , biology
1. Methods are described for using the changes in respiration of intact Libinia nerve to follow the rate of energy utilization by the sodium pump in this tissue. 2. Short tetani in 10 K(Na)ASW (artificial sea water in which Na is the major cation and the potassium concentration is 10 m M ) increased the oxygen uptake which then declined exponentially. From the net influx of Na during the tetanus and the associated oxygen uptake, values between 1·9 and 3·4 were calculated for the Na: ∼ P ratio. After longer tetani, the recovery curve was S‐shaped. 3. The pump was activated by potassium ions in the external medium and this activation was competitively inhibited by external sodium ions. The data are consistent with a Michaelis constant ( K m ) for external potassium of 1 m M and an inhibitor constant ( K i ) for external sodium of 60 m M . 4. In activating the pump, K could be replaced by Tl + , Rb, NH 4 and Cs ions; but, of the monovalent ions tested, sodium seemed to be unique in its inhibitory action. 5. In sea waters containing 460 m M ‐Na, ouabain behaved like a mixed inhibitor of the pump, reducing both the maximum velocity and the apparent affinity for external potassium. At a given ouabain concentration, reducing the sodium content of the medium was without effect on the maximum rate of pumping; but the apparent affinity for potassium increased more steeply than in a ouabain‐free solution. 6. The rate of energy utilization associated with pumping was unaffected by inclusion of quite high concentrations of sulphydryl‐blocking agents in the external medium.