Effects of external and internal K+ ions on magnesium block of inwardly rectifying K+ channels in guinea-pig heart cells

The Journal of Physiology
H Matsuda

Abstract

1. Block of the inwardly rectifying K+ channel by intracellular Mg2+ was studied in guinea-pig ventricular cells at varying external or internal K+ concentrations. Sucrose or glucose was mainly used as a substitute for K+. 2. The current-voltage (I-V) relation for the single channel, in the absence of internal Mg2+, was almost linear in 30 mM-external K+ and 150 mM-internal K+ (30 mM [K+]o) and in 45 mM-internal K+ and 150 mM-external K+ (45 mM [K+]i) as well as in 150 mM-external and internal K+ (the control condition). The channel conductance was 31.7 +/- 1.7 pS (mean +/- S.D., n = 36) in the control, 23.1 +/- 1.2 pS (n = 8) in 30 mM [K+]o and 29.7 +/- 1.3 pS (n = 16) in 45 mM [K+]i, respectively. 3. Mg2+ on the cytoplasmic side blocked the outward currents without affecting the inward currents. Outward mean open-channel currents were measured at different Mg2+ concentrations (0-100 microM) and voltages. The current-voltage relation rectified inwardly in the presence of internal Mg2+ in a voltage- and concentration-dependent manner. 4. Outward mean open-channel currents were normalized to that measured in the absence of Mg2+. The normalized current-voltage relation in 45 mM [K+]i was almost superimposable on that obtained in ...Continue Reading

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