Electrophysiology of the Sodium-Potassium-ATPase in Cardiac Cells

Abstract

Like several other ion transporters, the Na(+)-K(+) pump of animal cells is electrogenic. The pump generates the pump current I(p). Under physiological conditions, I(p) is an outward current. It can be measured by electrophysiological methods. These methods permit the study of characteristics of the Na(+)-K(+) pump in its physiological environment, i.e., in the cell membrane. The cell membrane, across which a potential gradient exists, separates the cytosol and extracellular medium, which have distinctly different ionic compositions. The introduction of the patch-clamp techniques and the enzymatic isolation of cells have facilitated the investigation of I(p) in single cardiac myocytes. This review summarizes and discusses the results obtained from I(p) measurements in isolated cardiac cells. These results offer new exciting insights into the voltage and ionic dependence of the Na(+)-K(+) pump activity, its effect on membrane potential, and its modulation by hormones, transmitters, and drugs. They are fundamental for our current understanding of Na(+)-K(+) pumping in electrically excitable cells.

Role of Na+/Ca2+exchanger in Ca2+homeostasis in rat suprachiasmatic nucleus neurons

“…As the Ca V 1.3 L-type Ca 2ϩ channel is activated at low voltages (Xu and Lipscombe 2001) and present in the SCN neurons (Huang et al 2012), the 0 Na ϩ -induced inhibition of TTX-resistant, nimodipine-sensitive Ca 2ϩ influx is likely mediated by deactivation of these channels as a result of membrane hyperpolarization. This explanation is reasonable, because the replacing ion Li ϩ has K ϩ -like action on the Na ϩ -K ϩ pump (Glitsch 2001) and at a concentration of 140 mM may enhance the Na ϩ -K ϩ pump to hyperpolarize the membrane potential of SCN neurons.…”

Ion Conductances in Supporting Cells Isolated From the Mouse Vomeronasal Organ

“…However, with our ionic conditions it was unlikely that Na ϩ ,K ϩ -ATPase could play any role in setting up V 0 in vomeronasal supporting cells. Intracellular Na ϩ concentration in the millimolar range is required for pump activity (e.g., Glitsch 2001). On the contrary, our standard pipette (intracellular) solution was nominally Na ϩ -free (see METHODS).…”

“…However, it is possible that Na ϩ influx through opened channels could cause a local increase in the intracellular Na ϩ concentration near the pump (the so-called "fuzzy space": Lederer et al 1990). This condition could be enhanced when using a highNa ϩ extracellular solution, while recording with a pipette solution in which K ϩ , a competitive inhibitor of Na ϩ at intracellular Na ϩ -binding sites of the pump (e.g., Glitsch 2001), is replaced by Cs ϩ (Fig. 2B, rightmost point).…”

Potentiation of EDHF-mediated relaxation by chloride channel blockers

“…This may be due to the different electrophysiological properties of K ir channels and Na + /K + ATPase. It is hitherto contradictory whether or not the Na + ,K + -ATPase is voltage-dependent [1,11] . However, K ir channels have been proved to be voltage-dependent [12] , which hyperpolarize cells by passing outward current in the voltage range just positive to the equilibrium potential of K + (E K ) [32] .…”

“…Cl -channels also play a key role in modulating the membrane potential of vascular smooth muscle [9] . Any change of the membrane potential can influence the activation states of voltage-dependent ion channels and their conductances [10][11][12][13] . As mentioned above, EDHF response is mediated through the activation of K ir channels and Na + /K + -ATPase.…”