AJP - Gastrointestinal and Liver Physiology, Vol 257, Issue 4 637-G643, Copyright © 1989 by American Physiological Society
Effect of cold temperature on membrane potential responses in opossum esophageal circular muscle
D. Kauvar, J. Crist and R. K. Goyal
Charles A. Dana Research Institute, Boston, Massachusetts.
The effects of cold temperature on resting membrane potential (RMP) and
membrane potential responses to depolarizing electrical current and
intramural nerve stimulation were examined in opossum esophageal circular
smooth muscle. Intracellular recordings were made in smooth muscle strips
obtained from 7 to 8 cm (proximal site) and 1 to 2 cm (distal site) above
the lower esophageal sphincter. RMP was not affected by changes in
temperature between 34 and 22 degrees C. Cooling caused progressive
inhibition of the amplitude and a slight increase in the duration of the
spike potential produced by depolarizing current. Cooling did not modify
the threshold for spike potential generation but decreased the spike
amplitude from 34.0 +/- 0.5 mV at 34 degrees C to 14.1 +/- 2.2 mV at 22
degrees C (P less than 0.01). Electrical field stimulation with single
electrical pulses (1.0 ms) produced tetrodotoxin-sensitive biphasic
membrane responses consisting of initial hyperpolarization, or an
inhibitory junction potential followed by depolarization that increased in
amplitude as temperature was decreased from 34 to 26 degrees C and then
decreased in amplitude as temperature was further decreased. At both
proximal and distal sites cooling from 34 to 22 degrees C caused more than
a twofold increase in the duration of hyperpolarization and time to peak
depolarization. However, the increase in the absolute time of the duration
of hyperpolarization and the time to peak depolarization was significantly
greater at the distal than proximal esophageal site. Cooling to 16 degrees
C decreased RMP and nearly abolished the biphasic membrane potential
response.(ABSTRACT TRUNCATED AT 250 WORDS)
