Na+/K+-pump and neurotransmitter membrane receptors

Abstract

Na⁺/K⁺-pump is an electrogenic transmembrane ATPase located in the outer plasma membrane of cells. The Na⁺/K⁺-ATPase pumps 3 sodium ions out of cells while pumping 2 potassium ions into cells. Both cations move against their concentration gradients. This enzyme's electrogenic nature means that it has a chronic role in stabilizing the resting membrane potential of the cell, in regulating the cell volume and in the signal transduction of the cell. This review will mainly consider the role of the Na⁺/K⁺-pump in neurons, with an emphasis on its role in modulating neurotransmitter receptor. Most of the literature on the modulation of neurotransmitter receptors refers to the situation in the mammalian nervous system, but the position is likely to be similar in most, if not all, invertebrate nervous systems.

Keywords: Na+/K+-pump; Neurotransmitter membrane receptors; Ouabain.

Fig. 1

A diagram showing the extrusion of 3 Na⁺ from the cell while 2 K⁺ entering the cell due to the activation of the Na⁺/K⁺-ATPase enzyme. This results in a raised concentration of intracellular K⁺ and a reduced concentration of intracellular Na⁺ relative to the interstitial fluid

Fig. 2

Structure of the cardiac glycoside, ouabain, a specific inhibitor of Na⁺/K⁺-ATPase

Fig. 3

A diagram to summarize a putative intracellular mechanism for a peptide-mediated reduction of neuron sensitivity to a chemical transmitter, for example, acetylcholine. P-R, peptide receptor; G-prot, G-protein; cADPR, cyclic adenosine diphosphate-ribose; ATP, adenosine triphosphate; IP₃, inositol-1,4,5-triphosphate; RY-R, ryanodine receptor; IP₃-R, IP₃ receptor; ACh-R, acetylcholine receptor; activation/increase of intracellular level, white/blue/orange arrow; inhibition of intracellular level, black arrow Modified from Pivovarov et al. (2007)