Temperature effect on carbachol-induced depression of spontaneous quantal transmitter release in frog neuromuscular junction.
The effects of carbachol (CCh) on the frequency (f) of the miniature endplate potentials were tested at temperatures between 5 and 30 degrees C. Higher CCh concentrations, 1 x 10(-5) and 5 x 10(-6) M, reduced the f to 60% and the temperature dependence was negligible. However, an inverse temperature dependence was found when low concentrations 3 x 10(-7) and 6 x 10(-7) M were applied. The depression of f was 40-50% in 5-10 degrees C but only 10-20% of the control in the 25 and 30 degrees C. During application of CCh, the new steady of f was reached at temperatures between 5 and 30 degrees C within 17-20 min (Q10 = 1.07). Much greater temperature dependence of recovery was observed during washing out CCh (Q10 = 1.6). The temperature-independence of the steady state effects of CCh, good agreement with Langmuir adsorption-desorption theory and non-steady kinetics indicate that physical rather than receptor-mediated events are responsible for the depression of f.
Strunsky
E G
EG
Kazan State Medical University, Russia.
Borisover
M D
MD
Nikolsky
E E
EE
Vyskocil
F
F
D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D008564:Membrane Potentials; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011896:Rana temporaria; D013696:Temperature
D018377:Neurotransmitter Agents; D002217:Carbachol