A transition temperature for acetylcholine channel conductance in chick myoballs.

1. The temperature dependence of ACh channel conductance (gamma) and channel open time (tau) was determined by analysing ACh induced membrane current fluctuations in voltage clamped chick myoballs. 2. gamma decreased from 25-30 pmho at 37 degrees C to less than 5 phmo at 10 degrees C. An Arrhenius plot of gamma vs. temperature exhibited a clear break or 'transition temperature' at 20 degrees C. 3. tau increased from 2 msec at 37 degrees C to 16 msec at 10 degrees C. The Arrhenius plot of tau vs. temperature was linear. No transition temperature was detected. 4. Submicellar concentrations of the non-ionic detergent, Triton X-100 reversibly blocked ACh respnses. The effect was all-or-none at the molecular level. 5. These results are consistent with the possibility that the fluidity of membrane lipids in the ACh receptor micro-environment may influence the degree to which the channel can open.