Sodium and Proton effects On Inward Proton Transport through Na/K Pumps (LB848)

Abstract

The Na/K pump (NKA) exports 3Na in exchange for 2K, across animal plasma membranes. Ion binding sites I&II can bind Na or K but site‐III exclusively binds Na in a voltage (V)‐dependent fashion. Without external Na or K the NKA imports H generating a current (IH). To crack IH relationship to ion interaction at their sites we investigated the characteristics of IH in ventricular myocytes and in Xenopus oocytes expressing ouabain‐resistant pumps. Lowering pH enlarged IH in both systems. In oocytes at pH 蠄5.6 a rapid increase in IH was followed by a slower inhibition (80% at pH 5). H‐activation was V‐dependent whilst H‐inhibition was V‐independent. In myocytes at pH 6 Nao stimulated IH at [Na] 蠄5 mM and inhibited at higher [Na]. In oocytes, only V‐independent Nao‐dependent inhibition was observed at pH 6 or 7.6 (K0.5~7 mM), but at pH 5 Na induced a nearly identical biphasic response than in myocytes at pH 6. Affinity for Ko was reduced (~10 fold) by pH 5 compared to pH 7.6. Our results suggest that H+ leak through site‐III, that binding of 2Na or 2H to sites‐I&II inhibit permeation and that NKA with mixed Na/H occupancy of sites‐I&II are also permeable to H. Supported by NSF MCB‐1243842.Grant Funding Source: NSF MCB‐1243842