Hyperpolarizing current of the Na/K ATPase contributes to the membrane polarization of the Purkinje cell in rat cerebellum

Abstract

The contribution of the Na/K ATPase (pump) current to the polarization of the Purkinje cell has been studied using slices of the rat cerebellum by blocking the pump with dihydro-ouabain (DHO) while recording the membrane potential with microelectrodes in the somata. From our recordings, it appeared that blocking the pump depolarized the Purkinje cells more rapidly than might be expected from shifts in Na+ and K+ concentrations, suggesting the removal of a hyperpolarizing current. Application of DHO, in the presence of tetrodotoxin (TTX), led to calcium spike firing and plateau-like discharges suggesting activation of voltage-dependent calcium channels in the dendrites. Adding 2 mM CO2+ to the medium did not prevent the depolarizations. Removing calcium from the bathing medium containing 2 mM CO2+ blocked the spiking activity but DHO application still produced a depolarization. Experiments to measure the current inhibited by DHO indicated that the Na/K pump supplies a constant current of 240 pA. Substitution of the sodium with choline produced a hyperpolarization, during which DHO had no effect on the membrane potential. Substitution of the sodium with lithium produced only a slowly developing depolarization. It is concluded that in the cerebellar Purkinje cell, a continuous sodium ion influx activates the pumps which produce a current that directly contributes to the membrane polarization. Possible pathways for this sodium influx are discussed.

Alcohol Excites Cerebellar Golgi Cells by Inhibiting the Na+/K+ ATPase

“…A submaximal concentration of ouabain, that produced equivalent inhibition of the Na + /K + ATPase current as ethanol, increased spontaneous action potential firing, depolarized the membrane potential and decreased the AHP in GoCs. Unlike ethanol, the effect of ouabain on these parameters was irreversible, which is in agreement with the literature and is expected because of the high affinity of this agent for the Na + /K + ATPase (Genet et al , 1997; Kim et al , 2007). The onset of the effect of ethanol on Na + /K + ATPase current, membrane potential and AHP matched closely that of ouabain.…”

“…The transport of 3 Na + ions out of the cell and 2 K + ions into the cell by the Na + /K + ATPase generates a net outward current that contributes to the maintenance of the resting membrane potential in neurons (for instance, see Genet and Kado, 1997) and acute exposure to ethanol has been shown to modulate the Na + /K + ATPase in preparations from rodent brains (Foley and Rhoads, 1994; Ledig et al , 1985; Syapin et al , 1985). We therefore assessed whether ethanol could affect GoC firing via modulation of the Na + /K + ATPase.…”

“…The Na + /K + ATPase was considered as a potential non-ion channel ethanol target because its electrogenic properties have been shown to play a role in controlling spontaneous firing, membrane potential, and membrane potential hyperpolarization in neurons (Genet et al , 1997; Kim et al , 2007; Munakata et al , 1998; Pulver and Griffith, 2010; Thompson and Prince, 1986; Wang and Huang, 2006). In addition, studies from several laboratories have demonstrated inhibition of the Na + /K + ATPase by acute ethanol exposure using brain homogenates, synaptosomes, microsomes or cultured neurons (Foster et al , 1989; Israel et al , 1965; Ledig et al , 1985; Rangaraj and Kalant, 1982; Swann, 1983; Syapin and Alkana, 1986; but see Foley et al , 1994).…”

Changes in the Distribution of theα3 Na+/K+ATPase Subunit in Heterozygous Lurcher Purkinje Cells as a Genetic Model of Chronic Depolarization during Development

“…The mature pump resides in the plasma membrane and exports 3 Na + ions for every two K + ions it imports at a cost of 1 ATP molecule, resulting in a net outward, hyperpolarizing current [1]. In healthy cerebellar Purkinje cells, increases in the expression levels of the Na/K pump during postnatal development are associated with the gradual hyperpolarization of the Purkinje cell membrane potential [2, 3]. All Na/K pumps contain an alpha ( α ) and a beta ( β ) unit, though in some cell types the pump contains an additional FXYD protein [4, 5].…”

“…Na/K ATPase activity in neurons may contribute as much as 240 pA to the resting membrane potential and pump activity is increased as a function of neuronal activity [3]. Changes in Na/K pump activity are also associated with the adaptive responses of neurons to hypoxia, ischemia, and cell death [5, 9].…”