23 January 1997, Volume 120, Issue 3, Pages 421 – 428

Article

The effect of the protein phosphatases inhibitor cantharidin on -adrenoceptor-mediated vasorelaxation Jörg Knapp1, Peter Bokník, Bettina Linck, Hartmut Lüss, Frank U. Müller, Peter Nacke, Joachim Neumann, Ute Vahlensieck & Wilhelm Schmitz Institut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität Münster, Germany     1Author for correspondence

Keywords

Phosphatases;   cantharidin;   bovine isolated coronary artery rings;   endothelial cells;   smooth muscle cells

Abstract

1   Cantharidin, an inhibitor of protein phosphatase types 1 (PP1) and 2A (PP2A), increased basal tone of bovine isolated coronary artery rings (CARs) with and without endothelium in a time- and concentration-dependent manner with pEC50 values of about 5.1 and 5.2, respectively, for both preparations. 2   -Adrenoceptor stimulation with isoprenaline (Iso; 0.03 – 100 µM) or inhibition of phosphodiesterase activity by 3-isobutyl-1-methylxanthine (IBMX; 10 – 1000 µM), respectively, relaxed CARs precontracted with KCl (75 mM). CARs with and without endothelium showed no difference in the relaxing response to Iso and IBMX, respectively. 3   Cantharidin (3 µM) attenuated vasorelaxation induced by Iso (0.03 – 100 µM) in CARs with and without endothelium in a time-dependent manner, whereas vasorelaxation induced by IBMX (10 – 1000 µM) was not attenuated by 3 µM cantharidin. 4   Cantharidin (3 µM) did not affect cyclic AMP content in bovine cultured vascular cells, i.e. coronary artery smooth muscle cells (BCs), aortic endothelial cells (BAECs) and aortic smooth muscle cells (BASMCs), either under basal conditions, after -adrenoceptor stimulation (Iso) or inhibition of phosphodiesterase activity (IBMX), respectively. 5   Cantharidin inhibited protein phosphatase activity in homogenates from bovine coronary artery rings with a pIC50 of about 6.0. In homogenates of bovine cultured vascular cells pIC50 values of cantharidin amounted to about 6.5 for BCs, 6.7 for BAECs and 6.7 for BASMCs, respectively. 6   It was concluded that cantharidin differently affects vasorelaxation due to stimulation of -adrenoceptors (Iso) or inhibition of phosphodiesterase activity (IBMX), respectively. The attenuation of -adrenoceptor-mediated vasorelaxation by phosphatase inhibition is not due to diminished adenosine 3′ : 5′-cyclic monophosphate (cyclic AMP) generation but could be evidence for different subcellular compartments of cyclic AMP.

Received 5 August, 96; Accepted 25 October, 96

^© Macmillan Publishers Ltd 1997