title: Na+/H+ exchanger-1 inhibitors reduce neuronal excitability and alter na+ channel inactivation properties in rat primary sensory neurons.
abstract: Inhibitors of the Na+/H+ exchanger isoform 1 (NHE-1) have been associated with peripheral neuropathy in rats and dogs. Recent studies suggest that NHE-1 plays an important role in mediating neuronal excitability. To investigate potential NHE-1-mediated mechanisms contributing to neuronal toxicity, we studied the effects of NHE-1 inhibitors on nerve and dorsal root ganglion (DRG) neurons isolated from the adult rat. Compound action potentials (CAPs) were recorded from electrically stimulated sections of isolated sciatic nerve/DRG/root preparations. Whole-cell patch-clamp technique was used to record fast and slow voltage-dependent Na+ currents from dissociated DRG neurons (29-41 microm). Exposures to 1 and 10 microM of a selective NHE-1 inhibitor reduced the amplitude of the CAP recorded from the dorsal root by 33% and 58%, respectively (p < 0.05). The compound had no effect on CAPs recorded from the ventral root. Perfusion of dissociated DRG neurons with NHE-1 inhibitors at 10 and 100 microM shifted voltage-dependent inactivation curves of fast Na+ current by as much as 11 mV (p < 0.001) in the hyperpolarizing direction. No shift was observed in slow Na+ currents. No statistically significant drug effects were observed on voltage-dependent activation or recovery from inactivation of either fast or slow Na+ currents. These results suggest that NHE-1 inhibitors may reduce peripheral neuronal excitability by shifting fast Na+ channels into the inactivated state under physiological conditions. Such effects may underlie peripheral neuropathies reported in rats and dogs with NHE-1 inhibitors.
authors.affiliation: Department of Investigative Toxicology, Drug Safety Research & Development, Pfizer Global R & D, Groton, Connecticut 06340, USA.
authors.forename: Chang-Ning
authors.initials: CN
authors.lastname: Liu
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Somps
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000187:drug effects*; D006146:Guanidines / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D011720:Pyrazoles / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*
chemical_list: D006146:Guanidines; D011720:Pyrazoles; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D017923:Sodium-Hydrogen Exchangers; C424422:zoniporide