A discontinuous relationship between the acetylcholine-activated channel conductance and temperature

SUMMARY1. Large spherical muscle cells were grown in vitro by allowing dissociated chick myoblasts to fuse in suspension culture.2. Myoball membranes could be adequately voltage clamped even in the face of large inward currents (ca. 100 nA) induced by ACh.3. The single channel conductance, y, estimated from the ratio of the mean to the variance of ACh currents was 25-40 pmho at temperatures between 250 and 37 0C. 4. Spectra of ACh current fluctuations declined with 1/f 2. The mean channel open time (7r) estimated from the half-power frequency was 2 msec at 37 0C and -90 mV holding potential. At lower membrane potentials 7 was decreased and on hyperpolarization r was prolonged.

Section: Introductionmentioning

confidence: 84%

Acetylcholine noise in cultured chick myoballs: a voltage clamp analysis.

Fischbach¹,

Lass²

1978

“…A 40 ,uM-ACh-filled pipette depolarized the membrane by only 1 mV at most. Assuming a myotube input resistance of 107 Q (Fischbach, Nameroff & Nelson, 1971), an ACh driving force of 50 mV, and a single channel conductance of 30 pmhos (Lass & Fischbach, 1976), it follows that a 1 mV ACh-induced depolarization represents the summed effect of no more than 100 open channels. Since the extracellular pipette covers about 20 ,um2 of surface membrane containing a total of roughly 18,000 ACh receptors (cf.…”

Section: Resultsmentioning

confidence: 99%

The acetylcholine channel open time in chick muscle is not decreased following innervation.

Schuetze¹

1980

“…We have used voltage clamped chick myoballs (Fischbach & Lass, 1978) to estimate the ACh channel conductance and mean open time over a wide range in temperature (5°-37 00). Some of the results have appeared in brief form (Lass & Fischbach, 1976).…”

Section: Introductionmentioning

confidence: 99%

A transition temperature for acetylcholine channel conductance in chick myoballs.

Fischbach¹,

Lass²

1978

3. X increased from 2 msec at 37 0C to 16 msec at 10 'C. The Arrhenius plot ofvs. temperature was linear. No transition temperature was detected.4. Submicellar concentrations of the non-ionic detergent, Triton X-100 reversibly blocked ACh responses. 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.