Voltage-dependent stimulation of Na+/K+-pump current by external cations: selectivity of different K+ congeners

Change of Na+ pump current reversal potential in sheep cardiac Purkinje cells with varying free energy of ATP hydrolysis.

“…However, it is helpful to realize that the mean values of the measured I,p are not significantly different from zero between -20 and -95 mV (Fig. 5) (Rakowski, Vasilets, La Tona & Schwarz, 1991;Omay & Schwarz, 1992) and freshly isolated rabbit cardiac Purkinje cells (Bielen et al 1993 …”

Apoptotic insults impair Na+, K+-ATPase activity as a mechanism of neuronal death mediated by concurrent ATP deficiency and oxidant stress

“…The Na + , K + -ATPase can be stimulated by external K + in a voltage-dependent manner (Vasilets et al, 1991;Omay and Schwarz, 1992). It is expected that following an excessive K + efflux and accumulation of extracellular K + , the Na + , K + -pump would be stimulated at least during some early period of apoptosis.…”

Na+ pump current‐voltage relationships of rabbit cardiac Purkinje cells in Na(+)‐free solution.

“…The concentrations for half-maximal Ip activation at zero membrane potential (KO.5(vc-mv)) differ by a factor of -30; TlV being the most potent, Cs+ the least potent pump activator (Table 1). Compared to the data obtained in Na+-containing media at -20 mV (Bielen et al 1991 Rakowski, Gadsby & DeWeer, 1989;Bielen et al 1991 a;review: Gadsby, 1984) or in Na+-free media (Rakowski et al 1989;Omay & Schwarz, 1992;Vasilets & Schwarz, 1992). The conclusion of the authors is that the electrogenic fraction is most probably independent of the external concentration of monovalent cations and the membrane potential.…”

“…Other experimental results are also in keeping with the idea of an 'ion well' within the membrane. They include the observations on the binding of K+ and its congeners to the Na+-K+ pump in Xenopus oocytes by Rakowski et al (1991) and Omay & Schwarz (1992). The latter authors pointed out that the apparent affinities of the binding site for the pump activator cations display the same sequence as does the permeability of the delayed rectifying K+ channels of neurons towards cations.…”

“…The negative slope of the Ip-Vm curve indicates a second voltage-dependent step in the pump cycle. Several observations suggest that binding of external K+ or other activator cations to the Na+-K' pump is the step involved (Rakowski, Vasilets, La Tona & Schwarz, 1991;Omay & Schwarz, 1992;Vasilets & Schwarz, 1992). In Na+-containing solution the cardiac Ip-Vm relationship exhibits a negative slope at positive potentials only if the activation of the Na+-K+ pump by extracellular activator cations is less than half-maximal.…”