On the cardiac contractile, electrophysiological and biochemical effects of endothall, a protein phosphatase inhibitor

Pharmacology. 2000 Jul;61(1):43-50. doi: 10.1159/000028379.


Protein phosphatase inhibitors, e.g. cantharidin, exert positive inotropic effects in mammalian heart preparations. Endothall, a synthetic herbicide which is chemically related to cantharidin, inhibits protein phosphatase activities in mouse liver preparations. However, the cardiac effects of endothall have hitherto not been studied. In guinea pig papillary muscles, endothall (1-100 micromol/l) failed to affect force of contraction, whereas cantharidin (1-100 micromol/l) increased force of contraction maximally to 313.4 +/- 32% of control at 10 micromol/l. In isolated guinea pig ventricular cardiomyocytes, endothall did neither change the free intracellular calcium concentration nor the amplitude of calcium current nor the phosphorylation state of regulatory phosphoproteins like phospholamban. In contrast, cantharidin (30 micromol/l) increased the free intracellular calcium concentration and the L-type calcium current to 149.6 +/- 9% and to 157.6 +/- 12% of control, respectively. Furthermore, cantharidin (1-100 micromol/l) augmented the phosphorylation of phospholamban maximally to 140.8 +/- 7% of control. Nevertheless, in guinea pig ventricular homogenates, both endothall and cantharidin inhibited phosphatase activity with EC(50) values of 1.92 and 0.32 micromol/l, respectively. Thus, in contrast to cantharidin, endothall failed to increase force of contraction, though it inhibited protein phosphatase activity. Clearly, endothall is not an appropriate tool to study the function of protein phosphatases in the mammalian heart.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium Channels, L-Type / drug effects
  • Calcium-Binding Proteins / metabolism
  • Dicarboxylic Acids / pharmacology*
  • Enzyme Inhibitors / pharmacology*
  • Guinea Pigs
  • Heart / drug effects*
  • In Vitro Techniques
  • Male
  • Myocardial Contraction / drug effects*
  • Phosphoprotein Phosphatases / antagonists & inhibitors*
  • Phosphoprotein Phosphatases / classification
  • Phosphoprotein Phosphatases / physiology
  • Phosphorylation


  • Calcium Channels, L-Type
  • Calcium-Binding Proteins
  • Dicarboxylic Acids
  • Enzyme Inhibitors
  • phospholamban
  • endothall
  • Phosphoprotein Phosphatases
  • Calcium