Potassium ion channel blockade restores conduction in heat-injured nerve and spinal nerve roots.
Compound action potentials were recorded in vitro from rat peroneal and sural nerves and from dorsal and ventral roots of the cauda equina before and after radiofrequency heating of 5-mm-length segments of these nerves to 41 to 45 degrees C. The heating was continued for intervals sufficient to reduce response amplitude by 50%. Inflection velocity, potential duration at 1/2 peak height, and the proportion of conducting A alpha fibers were also measured. The topical application of 4-aminopyridine (4-AP) and tetraethylammonium chloride (TEA) to the previously heated segments immediately following the radiofrequency injury completely or near-completely restored amplitude height to the preheat value in all experiments. A alpha sensory fibers were the most susceptible to the conduction block. Conduction in these fibers was also the most readily restored by the application of 4-AP or TEA. The effects of TEA, but not of 4-AP, could be reversed by saline or buffer washing. Topical application of verapamil and of magnesium or calcium ions had no discernible effect on heated nerves. We suggest that the mechanism of heat-induced conduction block may be similar to that from early demyelination or stretch injury. Further, motor and sensory A alpha fibers differ both in their vulnerability to heat and in their subsequent response to the application of potassium channel blockers.
D015761:4-Aminopyridine; D000200:Action Potentials; D000631:Aminopyridines / Q000627:therapeutic use*; D000818:Animals; D006358:Hot Temperature / Q000009:adverse effects*; D009431:Neural Conduction; D010523:Peripheral Nervous System Diseases / Q000188:drug therapy* / Q000209:etiology; D010543:Peroneal Nerve; D051381:Rats; D013126:Spinal Nerve Roots; D013497:Sural Nerve; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000627:therapeutic use*
D000631:Aminopyridines; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D015761:4-Aminopyridine