Pesticide Science (1996) 48, 375-388

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Melanie Schmitt, Andreas Turberg, Michael Londershausen and August Dorn (1996)
Binding sites for Ca2+-channel effectors and ryanodine in Periplaneta americana - Possible targets for new insecticides
Pesticide Science 48 (4), 375-388
Abstract: The calcium channel and the 'calcium' release channel of muscle membrane of the cockroach Periplaneta americana have been characterized. Biological assays with calcium channel blockers and ryanodine on different insects and acari revealed pronounced insecticidal effects with ryanodine, but not with calcium channel blockers, at concentrations between 0·1 and 300 µg ml-1. Skeletal muscle membranes derived either from the tubular network or from the sarcoplasmatic reticulum of P. americana were characterized with respect to the binding of the dihydropyridine (DHP) [3H]isradipine (PN 200-110), the phenyl-alkylamine [3H]verapamil and the alkaloid [3H]ryanodine. Preliminary binding studies with the benzothiazepine [3H]diltiazem suggest a low-affinity binding site with a IC50 value of 3·3 µM. All binding sites tested were sensitive to treatment with proteinase K. Optimal conditions for binding of the radioligand ryanodine revealed the highest specific binding at pH 8 and at calcium chloride concentrations between 100 and 500 µM. EGTA at 10 µM abolished 95% of the ryanodine binding. Binding studies with calcium channel binding sites revealed a pronounced effect of low Ca2+ concentrations on specific isradipine binding, whereas verapamil and diltiazem binding were only reduced by the presence of 200 µM EGTA. With respect to high Ca2+ concentrations, specific binding of diltiazem, isradipine and verapamil was reduced by 73, 40 and 20%, respectively, at 5 mM Ca2+. Radioligand binding experiments showed high-affinity binding sites for ryanodine and isradipine. KD values of 0·95 nM (Bmax=550 fmol mg-1 protein) and 0·75 nM (Bmax=213 fmol mg-1 protein) were determined respectively. A lower-affinity binding site was identified in binding studies with verapamil (KD=7·4 nM and Bmax=27 fmol mg-1 protein). [3H]isradipine displacement studies with several dihydropyridines revealed the following ranking of affinity: nitrendipine>isradipine>Bay K8664 <<nicardipine. Displacement of [3H]verapamil binding by effectors of the phenylalkylamine binding site showed that bepridil and S(-)verapamil had the highest affinities of the compounds tested followed by (±)verapamil, nor-methylverapamil and R(+)verapamil.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): August Dorn

Research topic(s) for pests/diseases/weeds:
control - general
molecular biology - genes


Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.


Periplaneta americana