An innovative method for rapid characterisation of phospholipase C activity: SB242,084 competitively antagonises 5-HT2C receptor-mediated [3H]phosphatidylinositol depletion

Naunyn Schmiedebergs Arch Pharmacol. 2000 Feb;361(2):221-3. doi: 10.1007/s002109900178.


6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) pyridin-3-ylcarbamoyl] indoline (SB242,084) is a novel, selective 5-HT(2C) receptor antagonist, but its actions at these sites have been little characterised at the cellular level. We employed a rapid and innovative approach to investigate its functional activity at phospholipase C (PLC)-coupled human 5-HT(2C) receptors expressed in CHO cells. PLC activity was determined as a decrease in the [3H]phosphatidylinositol ([3H]PI) content of cell membranes. Serotonin (5-HT) stimulated [3H]PI depletion (pEC50=8.74), and SB242,084, like mesulergine, completely reversed this action of 5-HT (pK(B)=9.25 and 9.01, respectively). Further, in Schild analysis, SB242,084 behaved as a high affinity competitive antagonist, inducing a parallel, rightward displacement of the 5-HT stimulation isotherm without loss of maximum efficacy. The pA2 of 9.50 was similar to its binding affinity (pKi=9.38). SB242,084 also displayed antagonist properties when PLC activity was examined by conventional determination of [3H]inositol phosphate generation. Employing this parameter, the potency of SB242,084 (pK(B)=9.21) and that of mesulergine (pK(B)=9.06) closely resembled those determined by [3H]PI depletion. In conclusion, determination of [3H]PI depletion constitutes a useful and novel technique to characterise agonist and antagonist properties of ligands at PLC-coupled receptors.

MeSH terms

  • Aminopyridines / pharmacology*
  • Animals
  • CHO Cells
  • Cricetinae
  • Ergolines / pharmacology
  • Humans
  • Indoles / pharmacology*
  • Phosphatidylinositols / metabolism*
  • Receptor, Serotonin, 5-HT2C
  • Receptors, Serotonin / drug effects*
  • Receptors, Serotonin / physiology
  • Serotonin / pharmacology
  • Serotonin Antagonists / pharmacology*
  • Type C Phospholipases / metabolism*


  • 6-chloro-5-methyl-1-((2-(2-methylpyrid-3-yloxy)pyrid-5-yl)carbamoyl)indoline
  • Aminopyridines
  • Ergolines
  • Indoles
  • Phosphatidylinositols
  • Receptor, Serotonin, 5-HT2C
  • Receptors, Serotonin
  • Serotonin Antagonists
  • Serotonin
  • Type C Phospholipases
  • mesulergine