The phospholipase C inhibitor U-73122 inhibits Ca(2+) release from the intracellular sarcoplasmic reticulum Ca(2+) store by inhibiting Ca(2+) pumps in smooth muscle

Br J Pharmacol. 2010 Jul;160(6):1295-301. doi: 10.1111/j.1476-5381.2010.00771.x.


Background and purpose: The sarcoplasmic reticulum (SR) releases Ca(2+) via inositol 1,4,5-trisphosphate receptors (IP(3)R) in response to IP(3)-generating agonists. Ca(2+) release subsequently propagates as Ca(2+) waves. To clarify the role of IP(3) production in wave generation, the contribution of a key enzyme in the production of IP(3) was examined using a phosphoinositide-specific phospholipase C (PI-PLC) inhibitor, U-73122.

Experimental approach: Single colonic myocytes were voltage-clamped in whole-cell configuration and cytosolic Ca(2+) concentration ([Ca(2+)](cyto)) measured using fluo-3. SR Ca(2+) release was evoked either by activation of IP(3)Rs (by carbachol or photolysis of caged IP(3)) or ryanodine receptors (RyRs; by caffeine).

Key results: U-73122 inhibited carbachol-evoked [Ca(2+)](cyto) transients. The drug also inhibited [Ca(2+)](cyto) increases, evoked by direct IP(3)R activation (by photolysis of caged IP(3)) and RyR activation (by caffeine), which do not require PI-PLC activation. U-73122 also increased steady-state [Ca(2+)](cyto) and slowed the rate of Ca(2+) removal from the cytoplasm. An inactive analogue of U-73122, U-73343, was without effect on either IP(3)R- or RyR-mediated Ca(2+) release.

Conclusions and implications: U-73122 inhibited carbachol-evoked [Ca(2+)](cyto) increases. However, the drug also reduced Ca(2+) release when evoked by direct activation of IP(3)R or RyR, slowed Ca(2+) removal and increased steady-state [Ca(2+)](cyto). These results suggest U-73122 reduces IP(3)-evoked Ca(2+) transients by inhibiting the SR Ca(2+) pump to deplete the SR of Ca(2+) rather than by inhibiting PI-PLC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aniline Compounds / chemistry
  • Animals
  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Carbachol / pharmacology
  • Colon / cytology
  • Cytosol / drug effects
  • Cytosol / metabolism
  • Estrenes / pharmacology*
  • Guinea Pigs
  • Inositol 1,4,5-Trisphosphate Receptors / drug effects
  • Inositol 1,4,5-Trisphosphate Receptors / metabolism
  • Male
  • Myocytes, Smooth Muscle / drug effects
  • Patch-Clamp Techniques
  • Phosphoinositide Phospholipase C / antagonists & inhibitors*
  • Pyrrolidinones / pharmacology*
  • Ryanodine Receptor Calcium Release Channel / drug effects
  • Ryanodine Receptor Calcium Release Channel / metabolism
  • Sarcoplasmic Reticulum / drug effects
  • Sarcoplasmic Reticulum / metabolism
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / antagonists & inhibitors*
  • Xanthenes / chemistry


  • Aniline Compounds
  • Estrenes
  • Inositol 1,4,5-Trisphosphate Receptors
  • Pyrrolidinones
  • Ryanodine Receptor Calcium Release Channel
  • Xanthenes
  • 1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione
  • Fluo-3
  • Caffeine
  • Carbachol
  • Phosphoinositide Phospholipase C
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases
  • Calcium