BINDING OF ALPHA-BUNGAROTOXIN TO CHICK SYMPATHETIC-GANGLIA - PROPERTIES OF RECEPTOR AND ITS RATE OF APPEARANCE DURING DEVELOPMENT

Studies were carried out on the binding of [125I].alpha.-bungarotoxin (.alpha.BT) to membrane fragments of chick sympathetic ganglia. Specific binding of toxin was saturable with a Kd of 1.1 nM. The rates of association and dissociation of the toxin from ganglionic membranes were 4.3 .times. 104 M-1 s-1 and 4.6 .times. 10-5 s-1 (t1/2 = 4.2 h), respectively. Binding was inhibited (by up to 95%) by low concentrations of nicotinic, but not by a muscarinic cholinergic ligand. The properties of the ganglionic binding site for .alpha.BT were consistent with its being a nicotinic acetylcholine receptor. The development of toxin receptors in chick ganglia was also studied. From days 7-11 in ovo, few receptors were present; from days 12-20 in ovo, there was a 10-fold increase in receptor number per ganglion; from hatching to maturity, the receptor number per ganglion slowly increased and reached a maximum of 14 f[femto]mol. The ontogeny of receptors for .alpha.BT in sympathetic ganglia appears to correlate with the cytological maturation and innervation of the principal neurons.