Summary
The Na pump current (Ip) was measured at 30–33 °C as a function of the extracellular K+ or Cs+ concentrations ([K]0; [Cs]0) by means of whole cell recording from cardioballs isolated from sheep Purkinje fibres. The results show that the magnitude of Ip is an s-shaped, saturating function of [K]0 or [Cs]0, respectively. Half maximal Ip activation occurs at 1.2 mM K0 or 3.2 mM Cs0 (clamp potential: −20 mV). These values are appceciably lower than earlier measurements on sheep Purkinje fibres indicated. The Hill coefficients for Ip activation by external K+ or Cs+ were calculated to be 1.94 and 1.73, respectively. The numbers suggest that Ip activation requires at least two external activator cations.
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Supported by the Deutsche Forschungsgemeinschaft (Forschergruppe ‘Konzell’)
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Glitsch, H.G., Krahn, T. & Verdonck, F. Activation of the Na pump current by external K and Cs ions in cardioballs from sheep Purkinje fibres. Pflugers Arch. 414, 99–101 (1989). https://doi.org/10.1007/BF00585634
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DOI: https://doi.org/10.1007/BF00585634