Characterization of subtypes of gamma-aminobutyric acid receptors in an Ascaris muscle preparation by binding assay and binding of PF1022A,a new anthelmintic,on the receptors |
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Authors: | W Chen M Terada J T Cheng |
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Institution: | (1) Department of Parasitology, Hammamatsu University School of Medicine, 3600 Handa-cho, Hammamatsu 431-31, Japan, JP;(2) Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan City, Taiwan 70101, Republic of China; Fax: + 886-6-238-6548, TW |
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Abstract: | We examined the effect of PF1022A, one of the gabergic anthelmintics newly developed in Japan, on gamma-aminobutyric acid
(GABA) receptors using a radioligand binding technique in isolated membrane preparations of the nematode Ascaris suum. Membrane protein was prepared from the homogenate of somatic muscle cells after ultracentrifugation. In addition to the basic
binding of 2,3-3H-(N)]-GABA, the radioligand methyl-3H]-bicuculline is used to identify the GABAA receptor, whereas butyl-4-3H]-baclofen is employed for GABAB receptor sites. The dissociation constants (K
d values) and the maximal numbers of binding sites (Bmax values) from Scatchard plotting for GABA receptors are close to those obtained in mammalian brain. PF1022A displaced in a
concentration-dependent way the binding of 2,3-3H(N)]-GABA and methyl-3H]-bicuculline as did other specific gabergic agents. In addition, PF1022A decreased the binding of butyl-4-3H]-baclofen at a higher concentration, although this binding did not represent GABAB sites. In a comparison of the inhibition constants (Ki values) of PF1022A with those of other agents, it is conclusive that PF1022A bound with GABA receptors. A direct effect of
PF1022A on GABA receptors can thus be postulated.
Received: 10 March 1995 / Accepted: 27 June 1995 |
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