MODIFICATION BY LOW TEMPERATURE OF 

 CERTAIN ION RESPONSES OF BULLFROG 

 NERVE FIBERS^ 



Frederick Crescitelli, Department of Zoology 

 University of California, Los Angeles, California 



HIS COMMUNICATION dcscribes a number of responses to sodium and to 

 potassium ions by the A and B fibers of the bullfrog sciatic-peroneal nerve 

 at normal and at low temperatures. The results demonstrate some notable 

 differences in these two fiber groups with regard to their reactions to low 

 temperature. This study is part of a larger program, from which some 

 data have already appeared (5, 6) , whose aim is to point out and to ana- 

 lyze differences in properties of different fiber groups in vertebrate periph- 

 eral nerves. In this introduction a review or analysis of the literature 

 concerned with the effects of temperature on nerve fibers will not be at- 

 tempted. Some summaries and enumeration of existing information have 

 appeared in the publications of Lorente de No (15), Hodgkin and Katz 

 (13), Hertz (11) and others. References to relevant literature will be 

 made in appropriate places in the body of this report. 



differential SENSITIVITY TO SODIUM AND TO POTASSIUM 

 AT NORMAL TEMPERATURE 



Following appropriate stimulation, the sciatic nerve of the bullfrog 

 (Rana cateshiana) yields a compound electrogram with three distinct 

 elevations known respectively as the A, B and C waves or action potentials 

 (fig. 1). These are known to represent activity in three different groups of 

 fibers each with characteristic physiological and pharmacological proper- 

 ties. At normal temperatures the A, B and C fiber groups react to solutions 

 with heightened potassium by a characteristic differential block of con- 

 duction at the treated portion of the nerve. These same fibers are also 

 l)locked selectively in response to solutions lacking sodium but this dif- 

 ferential block is qualitatively different from the high potassium action. 

 These points are illustrated by an experiment (fig. 1) which involved the 

 recording with a dual beam cathode ray oscillograph of the A, B and C 

 action potentials. The lower beam pictures the actions of all three fiber 

 groups while the upper trace shows, especially amplified, the B and C 

 activity. Record 1 is a control monophasic electrogram taken just before 



^ Aided l^y a giant from the Division of Research Grant.s and Fellowsliip.s, National 

 Institutes of Health, U.S. Public Health Service, and by a research grant from the 

 Board of Research, University of California. 



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