Sex differences in the acetylcholine receptor kinetics of postnatal and denervated rat muscle

1. Single-channel recording from visualised endplates in freshly dissociate d muscles from postnatal and denervated rat muscle revealed the presence of a low conductance. fetal type of acetylcholine receptor. 2. Kinetic analysis showed a main component in the burst durations with a m ean of 10.8 +/- 2.7 ms (n = 29). Receptors from female rats had an addition al 27.3 +/- 5.5 ms (n = 5) kinetic component which was found in one-third o f the 15 female endplates. 3. Recordings from male and female denervated muscles gave more homogeneous kinetics with single time constants of 7.2 +/- 1.3 and 7.4 +/- 1.3 ms, res pectively. 4. It is concluded that the acetylcholine receptor channels present during early development are different from those of denervated muscle.