Acta Univ Latv (2007) 723: 21–26

Investigation of ion selectivity in membranes of muscle cells

Abstract

The sequences of conductance ratios (GX/GK) and permeability ratios (PX/PK) for monovalent cations (X = Rb⁺, Cs⁺, Na⁺, Li⁺, NH₄⁺) were 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 before gramicidin treatment was K⁺ > Rb⁺ > Cs⁺ > NH₄⁺ > Na⁺ > Li⁺. In gramicidin channels of the same muscle fibre after addition of 5 × 10^–7 M or 1 × 10^–6 M gramicidin both the permeability and the conductance ratios had the sequence NH₄⁺ > Cs⁺ > Rb⁺ > K⁺ > Na⁺ > Li⁺.