Selectivity for cations in potassium and gramicidin channels of the muscle fibre membrane.
The sequences of conductance ratios (GX/GK) and permeability ratios (PX/PK) for monovalent cations (X = Rb+, Cs+, Na+, Li+, NH4+) have been studied in frog skeletal muscle before and after addition of the channel-forming antibiotic gramicidin A. The experiments were carried out under current clamp conditions using a double sucrose gap technique. For inwardly rectifying potassium channels the selectivity measured by membrane conductance ratios was K+ greater than Rb+ greater than Cs+ greater than NH4+ greater than Na+ greater than Li+. In gramicidin channels of the same muscle fibre both the permeability and the conductance ratios had the identical sequence NH4+ greater than Cs+ greater than Rb+ greater than K+ greater than Na+ greater than Li+. However, after external addition of Tl+ (2.5 x 10(-3) M to 20 x 10(-3) M) conductance and permeability ratios were different. The effect may result from specific binding of Tl+ in gramicidin channels.
Shvinka
N E
NE
Institute of Cytology, Academy of Sciences of the USSR, Leningrad.
Caffier
G
G
D000818:Animals; D002414:Cations, Monovalent; D002463:Cell Membrane Permeability; D004553:Electric Conductivity; D006096:Gramicidin / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008433:Mathematics; D008564:Membrane Potentials; D008962:Models, Theoretical; D009132:Muscles / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011893:Rana esculenta
D002414:Cations, Monovalent; D007473:Ion Channels; D015221:Potassium Channels; D006096:Gramicidin