Abstract
In this study we characterized the effects of the protein phosphatase (PP) type 1 and type 2A inhibitor cantharidin (Cant) and its structural analogs cantharidic acid and endothall on PP activity, force of contraction, and myosin light chain phosphorylation in rat aorta. All compounds inhibited PP activity in homogenates of rat aorta with a rank order of potency of Cant = cantharidic acid > endothall. However, only Cant increased force of contraction and myosin light chain phosphorylation in intact isolated rat aortic rings. Based on these findings, we investigated the effects of Cant on α-adrenoceptor-mediated vasoconstriction. Cant (1 and 3 μM) enhanced norepinephrine-induced contraction in endothelium-intact rat aorta. In contrast, Cant did not affect norepinephrine-induced contraction in endothelium-denuded rat aorta. We suggest that inhibition of PP1 and/or PP2A activities by Cant enhances vascular contractility in endothelium-intact rat aorta by increasing the phosphorylation state of endothelial regulatory proteins.
Footnotes
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Send reprint requests to: Dr. med. Jörg Knapp, Institut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität Münster, Domagkstraße 12, D-48129 Münster, FRG. E-mail: jknapp{at}uni-muenster.de
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↵1 This study was supported by the Deutsche Forschungsgemeinschaft and the Interdisziplinäres Zentrum für Klinische Forschung, Münster.
- Abbreviations:
- MLC20
- regulatory light chains of myosin (20 kDa)
- PP
- serine/threonine protein phosphatase
- OA
- okadaic acid
- Cant
- cantharidin
- CA
- cantharidic acid
- ETA
- endothall
- NE
- norepinephrine
- KHS
- Krebs-Henseleit solution
- CB
- carbachol
- 2D-PAGE
- two-dimensional polyacrylamide gel electrophoresis
- DMSO
- dimethyl sulfoxide
- NOS
- nitric-oxide synthase
- NO
- nitric oxide
- eNOS
- endothelial NOS
- PLB
- phospholamban
- pD2
- −log EC50
- Received December 21, 1999.
- Accepted May 1, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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