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The Na pump is examined in sheep cardiac Purkinje fibres using a two micro-electrode voltage clamp technique.2. After reducing the external K concentration, K(o), to zero for 2 min or more, subsequent addition of an ;activator cation' (known to activate the Na pump in other preparations) produces a transient increase of outward current. This outward current transient is abolished by 10(-5)M-strophanthidin (cf. Gadsby activator cations', the outward current transient is relatively voltage independent over a wide range of potentials (-90 to +10 mV). It is concluded that, following the addition of Rb(o) or Cs(o), the transient increase of outward current is a direct measure of the transient increase of the electrogenic Na pump current.5. Increasing Rb(o) or Cs(o) over the range of 0-40 mM increases the rate of decay of the electrogenic Na pump current transient. Using a simple model (cf. Rang activator cations'. This measure can be used in the intact preparation to investigate the relationship between Na pump rate and other cellular events such as the regulation of tension (Eisner & Lederer, 1980).
Eisner et al. (Sun,) studied this question.