A non-capacitative pathway activated by arachidonic acid is the major Ca2+ entry mechanism in rat A7r5 smooth muscle cells stimulated with low concentrations of vasopressin

J Physiol. 1999 May 15;517 ( Pt 1)(Pt 1):121-34. doi: 10.1111/j.1469-7793.1999.0121z.x.


1. Depletion of the Ca2+ stores of A7r5 cells stimulated Ca2+, though not Sr2+, entry. Vasopressin (AVP) or platelet-derived growth factor (PDGF) stimulated Sr2+ entry. The cells therefore express a capacitative pathway activated by empty stores and a non-capacitative pathway stimulated by receptors; only the former is permeable to Mn2+ and only the latter to Sr2+. 2. Neither empty stores nor inositol 1,4,5-trisphosphate (InsP3) binding to its receptors are required for activation of the non-capacitative pathway, because microinjection of cells with heparin prevented PDGF-evoked Ca2+ mobilization but not Sr2+ entry. 3. Low concentrations of Gd3+ irreversibly blocked capacitative Ca2+ entry without affecting AVP-evoked Sr2+ entry. After inhibition of the capacitative pathway with Gd3+, AVP evoked a substantial increase in cytosolic [Ca2+], confirming that the non-capacitative pathway can evoke a significant increase in cytosolic [Ca2+]. 4. Arachidonic acid mimicked the effect of AVP on Sr2+ entry without stimulating Mn2+ entry; the Sr2+ entry was inhibited by 100 microM Gd3+, but not by 1 microM Gd3+ which completely inhibited capacitative Ca2+ entry. The effects of arachidonic acid did not require its metabolism. 5. AVP-evoked Sr2+ entry was unaffected by isotetrandrine, an inhibitor of G protein-coupled phospholipase A2. U73122, an inhibitor of phosphoinositidase C, inhibited AVP-evoked formation of inositol phosphates and Sr2+ entry. The effects of phorbol esters and Ro31-8220 (a protein kinase C inhibitor) established that protein kinase C did not mediate the effects of AVP on the non-capacitative pathway. An inhibitor of diacylglycerol lipase, RHC-80267, inhibited AVP-evoked Sr2+ entry without affecting capacitative Ca2+ entry or release of Ca2+ stores. 6. Selective inhibition of capacitative Ca2+ entry with Gd3+ revealed that the non-capacitative pathway is the major route for the Ca2+ entry evoked by low AVP concentrations. 7. We conclude that in A7r5 cells, the Ca2+ entry evoked by low concentrations of AVP is mediated largely by a non-capacitative pathway directly regulated by arachidonic acid produced by the sequential activities of phosphoinositidase C and diacylglycerol lipase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arachidonic Acid / metabolism*
  • Arginine Vasopressin / pharmacology*
  • Calcium / metabolism*
  • Cell Line
  • Gadolinium / pharmacology
  • Ion Transport / drug effects
  • Manganese / metabolism
  • Muscle, Smooth, Vascular / cytology
  • Muscle, Smooth, Vascular / drug effects*
  • Muscle, Smooth, Vascular / metabolism*
  • Phosphoric Diester Hydrolases / metabolism
  • Rats
  • Strontium / metabolism


  • Arginine Vasopressin
  • Arachidonic Acid
  • Manganese
  • Gadolinium
  • Phosphoric Diester Hydrolases
  • glycerophosphoinositol glycerophosphodiesterase
  • Calcium
  • Strontium