Key result
Increasing internal (pipette) sodium (Napip) in adult rat cardiac myocytes increased both the maximal Na-K pump current and the apparent affinity for external potassium binding.
Why the study?
Does varying internal sodium concentration influence the external potassium dependence of the Na-K pump current in adult rat cardiac myocytes?
Does varying internal sodium concentration influence the external potassium dependence of the Na-K pump current in adult rat cardiac myocytes?
In adult rat cardiac myocytes, the apparent affinity for external potassium binding to the Na-K pump increases as internal sodium concentration increases.
Internal Na effects on Na-K pump K affinity in rat myocytes warrant clinical caution; leaves open human relevance.
To determine if environmental factors influence the external K (K0) dependence of Na-K pump current (Ip), we systematically varied internal (pipette) Na (Napip) and Na-K pump activity while measuring the K0 dependence in adult rat cardiac myocytes. For each Napip, reactivation of Ip by K0 was dose dependent. The maximal Ip (Ipmax) and apparent affinity for K0 binding to the Na-K pump (K0.5) increased as Napip increased. The results of making an equimolar substitution of tetramethylammonium for K and Cs, and partial Ip inhibition with ouabain, also showed that Ipmax and K0.5 increased as Napip increased. We simulated pump activity as a function of intracellular Na (Nai) and K0 using a cyclic model of the Na-K pump and found that the model predicts K0.5 for K0 binding increases as Na increases, even when the conditions are adjusted by removing pipette K and partial pump inhibition with ouabain.
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Kinard et al. (1994) studied this question. Internal (pipette) Na (Napip) was evaluated on K0 dependence of Na-K pump current (Ip). Increasing internal (pipette) sodium (Napip) in adult rat cardiac myocytes increased both the maximal Na-K pump current and the apparent affinity for external potassium binding.
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