Multiplicity of receptors for vasoactive intestinal polypeptide (VIP): differential effects of apamin on binding in brain, uterus and liver |
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| Authors: | Jan Fahrenkrug Steen Gammeltoft Poul Staun-Olsen Bent Ottesen Anders Sjöquist |
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| Institution: | 1. Department of Clinical Chemistry, Bispebjerg, Denmark;2. Department of Glostrup, Bispebjerg, Denmark;3. Department of Rigshospital, Denmark;4. Institute of Medical Physiology B, University of Copenhagen, Denmark;5. Panum Institute, University of Copenhagen, Denmark;6. Department of Physiology, University of Gothenburg, Sweden |
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| Abstract: | Apamin is a neurotoxic octadecapeptide from bee venom, which has been shown to inhibit the non-adrenergic, non-cholinergic inhibitory innervation of the smooth muscle of the gut. Since vasoactive intestinal polypeptide (VIP) has been proposed as a possible inhibitory neurotransmitter, the effect of apamin on the receptor binding of 125I-VIP was studied using the following assays: (1) isolated synaptosomes from rat cerebral cortex, (2) crude plasma membranes from hog uterine smooth muscle, and (3) purified plasma membranes and isolated hepatocytes from hog liver. Apamin inhibited the receptor-bound 125I-VIP on membranes from brain or myometrium, although the binding affinity was 100-1000 times lower than for VIP. The displacement curves for VIP and apamin were parallel suggesting that apamin interacts with both the low and high affinity VIP receptors. In membranes and cells from liver, apamin was unable to displace receptor-bound 125I-VIP in concentrations up to 50 mumol/l. The findings suggest that the VIP receptors in liver are different from those in the brain cortex and myometrium. |
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| Keywords: | Neurotoxin Binding sites Neuropeptide Cerebral cortex Synaptosomes Uterine smooth muscle membranes Liver cells Liver membranes |
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