Effects of X-rays Combined with Other Agents on the Excitability of Frog Sciatic Nerve

Summary The increased excitability (measured as a change in amplitude of monophasic sub-maximal action potentials in a humid chamber) of the isolated sciatic nerve of frog to electrical stimulation after a radiation dose of 10 krads of 50 kV x-rays has been found to be independent of the oxygen content of the atmosphere surrounding the nerve. Increasing the carbon dioxide content of the atmosphere has been found to give an 'apparent' increase in the radiation response. However, this increase is due to a radiation reversal of the neural membrane hyperpolarization induced by the carbon dioxide. Increasing the hydrogen ion concentration of the extracellular fluid has been found to reduce the radiation response, whereas radiation enhances the blocking action on the nerve action potential of low concentrations of cocaine. It is postulated that the results of the combined effects of radiation and each of the membrane stabilizers carbon dioxide and cocaine are due to a transient increase of intra-membrane pH induced by the radiation.