Muscarinic cholinergic receptors in lung of developing rats

The muscarin-specific radioligand 1-quinuclidinyl-[phenyl-4-3H]-benzilate was used to determine the development of muscarinic receptors in particulate membranes of rat lung. Postnatal development is associated with a decrease in the number of binding sites (Bmax). Bmax was 65.61 +/- 11.33 fmol/mg protein in 21-day-old rat fetuses and it decreased to 36.64 +/- 10.18 at postnatal day 1, 32.37 +/- 4.99 at day 7 and 16.15 +/- 4.13 fmol/mg protein at 2 months. Bmax at 2 months was significantly different from all the others (Dunnett's test). The dissociation constant Kd was 0.25 nM in 2-month-old animals and it did not undergo significant changes during development.