Changes in Temperature Have Opposing Effects on Current Amplitude in α7 and α4β2 Nicotinic Acetylcholine Receptors

Marie Jindrichova,Neil S Millar,Stuart J Lansdell,Jon T Brown

doi:10.1371/journal.pone.0032073

Abstract

We have examined the effect of temperature on the electrophysiological properties of three neuronal nicotinic acetylcholine receptor (nAChR) subtypes: the rapidly desensitizing homomeric α7 nAChR, the more slowly desensitizing heteromeric α4β2 nAChR and on α7 nAChRs containing a transmembrane mutation (L247T) that results in dramatically reduced desensitization. In all cases, the functional properties of receptors expressed in Xenopus oocytes at room temperature (RT; 21°C) were compared to those recorded at either physiological temperature (37°C) or at lower temperature (4°C). Alterations in temperature had dramatically differing effects on the amplitude of whole-cell responses detected with these three nAChR subtypes. Compared to responses at RT, the amplitude of agonist-evoked responses with α4β2 nAChRs was increased at high temperature (125±9%, n = 6, P<0.01) and reduced at low temperature (47±5%, n = 6, P<0.01), whereas the amplitude of α7 responses was reduced at high temperature (27±7%, n = 11, P<0.001) and increased at low temperatures (224±16%, n = 10, P<0.001). In contrast to the effects of temperature on α4β2 and wild type α7 nAChRs, the amplitude of α7 nAChRs containing the L247T mutation was unaffected by changes in temperature. In addition, changes in temperature had little or no effect on current amplitude when α7 nAChRs were activated by the largely non-desensitizing allosteric agonist 4BP-TQS. Despite these differing effects of temperature on the amplitude of agonist-evoked responses in different nAChRs, changes in temperature had a consistent effect on the rate of receptor desensitization on all subtypes examined. In all cases, higher temperature resulted in increased rates of desensitization. Thus, it appears that the differing effects of temperature on the amplitudes of whole-cell responses cannot be explained by temperature-induced changes in receptor desensitization rates.

Highlights

Nicotinic acetylcholine receptors are members of the Cys-loop family of ligand-gated ion channels which includes receptors for 5-hydroxytryptamine (5-HT), c-aminobutyric acid (GABA) and glycine [1]
When acetylcholine-evoked responses were recorded at room temperature (RT; 21uC), rapidly desensitizing currents were observed (Fig. 1), typical of a7 nicotinic acetylcholine receptor (nAChR) [13]
Changes in current amplitude or in the rate of receptor desensitization were found to be reversible. It has been known for several decades that changes in temperature can influence the properties of nAChRs

Summary

Introduction

Nicotinic acetylcholine receptors (nAChRs) are members of the Cys-loop family of ligand-gated ion channels which includes receptors for 5-hydroxytryptamine (5-HT), c-aminobutyric acid (GABA) and glycine [1]. In common with other Cys-loop receptors, nAChRs are oligomeric transmembrane proteins in which five subunits co-assemble to form a central ion-channel pore [2]. Subunits of Cys-loop receptors share a common transmembrane topology, containing an extracellular N-terminal region and four a-helical transmembrane domains [1]. Two nAChR subtypes (heteromeric a4b2 nAChRs and homomeric a7 nAChRs) have attracted particular attention as targets for pharmaceutical drug discovery. Homomeric a7 nAChRs have high calcium permeability and very rapid desensitization. They have been identified as potential drug targets in treatment of disorders such as Alzheimer’s disease and schizophrenia [4,5,6]. A4b2 nAChRs are targets for drug discovery in areas such as cognition, attention and pain [4,5,6]

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Conclusion