Receptors linked to polyphosphoinositide hydrolysis stimulate Ca2+ extrusion by a phospholipase C-independent mechanism

Biochem J. 1999 Aug 15;342 ( Pt 1)(Pt 1):199-206.

Abstract

In A7r5 cells with empty intracellular Ca(2+) stores in which the cytosolic free Ca(2+) concentration ([Ca(2+)](i)) had been increased by capacitative Ca(2+) entry, stimulation of receptors linked to phospholipase C (PLC), including those for Arg(8)-vasopressin (AVP) and platelet-derived growth factor (PDGF), caused a decrease in [Ca(2+)](i.) This effect was further examined in a stable variant of the A7r5 cell line in which the usual ability of hormones to stimulate non-capacitative Ca(2+) entry is not expresssed. In thapsigargin-treated cells, neither AVP nor PDGF affected capacitative Mn(2+) or Ba(2+) entry, but both stimulated the rate of Ca(2+) extrusion, and their abilities to decrease [Ca(2+)](i) were only partially inhibited by removal of extracellular Na(+). These results suggest that receptors linked to PLC also stimulate plasma membrane Ca(2+) pumps. Activation of protein kinase C by phorbol 12, 13-dibutyrate (PDBu, 1 microM) also caused a decrease in [Ca(2+)](i) by accelerating Ca(2+) removal from the cytosol; the effect was again only partially inhibited by removal of extracellular Na(+). An inhibitor of PKC, Ro31-8220 (10 microM), abolished the ability of PDBu to decrease [Ca(2+)](i), without affecting the response to maximal or submaximal concentrations of AVP. Similar experiments with PDGF were impracticable because Ro31-8220, presumably by inhibiting the tyrosine kinase activity of the PDGF receptor, abolished all responses to PDGF. U73122 (10 microM), an inhibitor of PLC, completely inhibited PDGF- or AVP-evoked Ca(2+) mobilization, without preventing either stimulus from causing a decrease in [Ca(2+)](i). We conclude that receptors coupled to PLC, whether via G-proteins or protein tyrosine kinase activity, also share an ability to stimulate the plasma membrane Ca(2+) pump via a mechanism that does not require PLC activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arginine Vasopressin / antagonists & inhibitors
  • Arginine Vasopressin / pharmacology
  • Calcium / metabolism*
  • Calcium Signaling / drug effects
  • Calcium-Transporting ATPases / metabolism
  • Cations, Divalent / metabolism
  • Cell Line
  • Cytosol / drug effects
  • Cytosol / enzymology
  • Cytosol / metabolism
  • Enzyme Activation / drug effects
  • Hydrolysis / drug effects
  • Muscle, Smooth, Vascular / cytology
  • Muscle, Smooth, Vascular / drug effects
  • Muscle, Smooth, Vascular / enzymology
  • Muscle, Smooth, Vascular / metabolism
  • Phorbol 12,13-Dibutyrate / pharmacology
  • Phosphatidylinositol Phosphates / metabolism*
  • Platelet-Derived Growth Factor / antagonists & inhibitors
  • Platelet-Derived Growth Factor / pharmacology
  • Protein Kinase C / antagonists & inhibitors
  • Protein Kinase C / metabolism
  • Rats
  • Receptors, Cell Surface / metabolism*
  • Sodium / metabolism
  • Thapsigargin / pharmacology
  • Type C Phospholipases / antagonists & inhibitors
  • Type C Phospholipases / metabolism*

Substances

  • Cations, Divalent
  • Phosphatidylinositol Phosphates
  • Platelet-Derived Growth Factor
  • Receptors, Cell Surface
  • Arginine Vasopressin
  • Phorbol 12,13-Dibutyrate
  • Thapsigargin
  • Sodium
  • Protein Kinase C
  • Type C Phospholipases
  • Calcium-Transporting ATPases
  • Calcium