Receptors linked to polyphosphoinositide hydrolysis stimulate Ca2+ extrusion by a phospholipase C-independent mechanism.
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.
Broad
L M
LM
Department of Pharmacology, Tennis Court Road, Cambridge CB2 1QJ, UK.
Cannon
T R
TR
Short
A D
AD
Taylor
C W
CW
D000818:Animals; D001127:Arginine Vasopressin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006868:Hydrolysis / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D002413:Cations, Divalent; D018129:Phosphatidylinositol Phosphates; D010982:Platelet-Derived Growth Factor; D011956:Receptors, Cell Surface; D001127:Arginine Vasopressin; D015240:Phorbol 12,13-Dibutyrate; D019284:Thapsigargin; D012964:Sodium; D011493:Protein Kinase C; D010738:Type C Phospholipases; D000252:Calcium-Transporting ATPases; D002118:Calcium