Abbreviations: Nav, voltage-gated sodium channel; TTX, tetrodotoxin; ProTxII, Ī²/Ļ-theraphotoxin-Tp2a; Ca 2+ , calcium ion; DMEM, Dulbecco's Modified Eagle's Medium; FBS, foetal bovine serum; PBS, phosphate buffered saline; PSS, physiological salt solution; HBS, HEPES-buffered saline; AFU, arbitrary fluorescence unit; SEM, standard error of the mean; Fluo-4 AM, Fluo-4 acetoxymethylester; RPMI, Roswell Park Memorial Institute; BSA, bovine serum albumin; CCD, charge-coupled device; DAPI, 4',6-diamidino-2-phenylindole 2
AbstractThe human neuroblastoma cell line SH-SY5Y is a potentially useful model for the identification and characterisation of Nav modulators, but little is known about the pharmacology of their endogenously expressed Navs. The aim of this study was to determine the expression of endogenous Nav Ī± and Ī² subunits in SH-SY5Y cells using PCR and immunohistochemical approaches, and pharmacologically characterise the Nav isoforms endogenously expressed in this cell line using electrophysiological and fluorescence approaches. SH-SY5Y human neuroblastoma cells were found to endogenously express several Nav isoforms including Nav1.2 and Nav1.7. Activation of endogenously expressed Navs with veratridine or the scorpion toxin OD1 caused membrane depolarization and subsequent Ca 2+ influx through voltage-gated L-and N-type calcium channels, allowing Nav activation to be detected with membrane potential and fluorescent Ca 2 dyes. ļ-Conotoxin TIIIA and ProTxII identified Nav1.2 and Nav1.7 as the major contributors of this response. The Nav1.7-selective scorpion toxin OD1 in combination with veratridine produced a Nav1.7-selective response, confirming that endogenously expressed human Nav1.7 in SH-SY5Y cells is functional and can be synergistically activated, providing a new assay format for ligand screening.Key Words: SH-SY5Y; Ca 2+ ; Nav1.7; ProTxII; OD1 3
IntroductionVoltage-gated sodium channels (Nav) are complex transmembrane proteins comprised of a poreforming Ī± subunit and accessory Ī² subunits that play an essential role in the initiation and propagation of action potentials in excitable cells. To date, apart from the related Nax which appears to function as a sodium sensor [1,2], nine isoforms termed Nav1.1 -Nav1.9 have been functionally defined as sodium-selective ion channels [3]. Their distinct tissue distribution and amenability to modulation by toxins and drugs has led to significant interest in Nav as therapeutic targets in a number of poorly treated conditions ranging from epilepsy to cardiac arrhythmias and pain [4]. In recent years Nav1.7 has emerged as an attractive drug target, with expression restricted to a subset of nociceptive neurons that is expected to limit on-target side effects of pharmacological modulators of Nav1.7 [5]. In addition, loss-of-function mutations in humans have highlighted the possibility that Nav1.7 inhibition could produce complete loss of pain sensations without dose-limiting side effects [6]. However, it remains unclear if such an effect can be translated to the clinic...