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Nicotinic and muscarinic cholinergic receptors in honey bee (Apis mellifera) brain

1990; Elsevier BV; Volume: 97; Issue: 2 Linguagem: Inglês

10.1016/0742-8413(90)90141-u

1878-1969

Zhiyong Huang, Charles O. Knowles,

Cholinesterase and Neurodegenerative Diseases

1. Honey bee head homogenates contained particulate components capable of binding the nicotinic receptor antagonist α-bungarotoxin (BGT) and the muscarinic receptor antagonist quinuclidinyl benzilate (QNB). Specific binding of [125I]BGT (denned by nicotine) and [3H]QNB (defined by atropine) was heat sensitive, linear with tissue concentration, and saturable. Bmax values were 204 fmol mg protein−1 for [125I]BGT and 57 fmol mg protein−1 for [3H]QNB yielding a binding site ratio of 3.6:1. Hill coefficients were 1.0 for each radioligand. 2. Binding by both radioligands was rapid and reversible. Association (k+1) and dissociation (k−1) rates were 1.38 × 106 s−1 M−1 and 6.2 × 10−4 s−1 for [125I]BGT and 3.27 × 106 s−1 M−1 and 9.4 × 10−5 s−1 for [3H]QNB. The dissociation rate constants (KD) were 450 pM (k−1k+1) and 743 pM (saturation) for [125I]BGT and 30pM (k−1k+1) and 96 pM (saturation) for [3H]QNB. 3. Pharmacological profiles were nicotinic for [125I]BGT with nicotine (Ki 2.6 × 10−7 M), d-tubocurarine (Ki 1.0 × 10−6 M), and ACh + dichlorvos (Ki 4.5 × 10−6 M) being the most potent inhibitors and muscarinic for [3H]QNB with (±)-QNB (Ki 2.2 × 10−12M), S( + )-dexetimide (Ki 2.9 × 10−11 M), atropine (Ki 6.9 × 10−10M), and scopolamine (Ki 4.1 × 10−10M) being most potent. 4. It appeared that [125I]BGT and [3H]QNB were binding with high affinity to honey bee brain populations of nicotinic and muscarinic cholinergic receptors, respectively.