Effects of potassium ions on action potential conduction in A- and C-fibers of rat spinal nerves.
Potassium ions in dentifrices for treating 'hypersensitive' dentin are believed to act directly on intradental nerves by raising extracellular potassium ion concentration ([K+]o) sufficiently to prevent action potential generation by axonal accommodation. However, the [K+]o necessary to block nerve conduction is not precisely known, nor is it certain that K+ can diffuse from a dentifrice in sufficient amounts to inactivate intradental nerves. To establish more accurately the [K+]o required to block nerve conduction under controlled conditions, we studied the effects of increased [K+]o on the sizes of compound action potentials (CAP) recorded from rat spinal nerves in vitro. [K+]o was increased by the addition of either KCl or KNO3 to Krebs' solutions applied to the central portion of the nerves. CAP attenuation increased in a dose-dependent manner as [K+]o was raised in the 8 to 64 mmol/L range, and complete block was generally produced with solutions containing at least 32 mmol/L K+. CAP attenuation was reversible, and recovery times increased with increasing [K+]o. The effects of KCl and KNO3 solutions were the same for all [K+]o tested. Half-maximal (50%) reduction in the A beta-fiber component of the CAP occurred with 17.4 mmol/L K+, and with 17.8 mmol/L and 19.3 mmol/L K+, respectively, for the A delta- and C-fiber components. Control experiments with glucose and choline chloride confirmed that the conduction block observed with increased [K+]o was not due to increased solution osmolarity or ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)
Peacock
J M
JM
Institute of Physiology, University of Glasgow, Scotland, United Kingdom.
Orchardson
R
R
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001369:Axons / Q000187:drug effects*; D003807:Dentin Sensitivity / Q000188:drug therapy / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D008297:Male; D009431:Neural Conduction / Q000187:drug effects*; D009994:Osmolar Concentration; D011188:Potassium / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013126:Spinal Nerve Roots / Q000187:drug effects; D018709:Statistics, Nonparametric
D011188:Potassium