P2 receptor-mediated signal transduction in Ehrlich ascites tumor cells

Abstract

The mechanisms, by which the P2 receptor agonists adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP) evoke an increase in the free cytosolic calcium concentration ([Ca2+]i) and in intracellular pH (pHi), have been investigated in Ehrlich ascites tumor cells. The increase in [Ca2+]i evoked by ATP or UTP is abolished after depletion of intracellular Ca2+ stores with thapsigargin in Ca2+-free medium, and is inhibited by U73122, an inhibitor of phospholipase C (PLC), indicating that the increase in [Ca2+]i is primarily due to release from intracellular, Ins(1,4,5)P3-sensitive Ca2+ stores. ATP also activates a capacitative Ca2+-entry pathway. ATP as well as UTP evokes a biphasic change in pHi, consisting of an initial acidification followed by alkalinization. Suramin and 4,4'-diisothiocyano-2,2'-stilbene-disulfonic acid (DIDS) inhibit the biphasic change in pHi, apparently by acting as antagonists at P2 receptors. The alkalinization evoked by the P2 receptor agonists is found to be due to activation of a 5'-(N-ethyl-N-isopropyl)amiloride (EIPA)-sensitive Na+/H+ exchanger. ATP and UTP elicit rapid cell shrinkage, presumably due to activation of Ca2+ sensitive K+ and Cl- efflux pathways. Preventing cell shrinkage, either by incubating the cells at high extracellular K+ concentration, or by adding the K+-channel blocker, charybdotoxin, does not affect the increase in [Ca2+]i, but abolishes the activation of the Na+/H+ exchanger, indicating that activation of the Na+/H+ exchanger is secondary to the Ca2+-induced cell shrinkage.

Ion Channels Involved in Cell Volume Regulation: Effects on Migration, Proliferation, and Programmed Cell Death in Non Adherent EAT Cells and Adherent ELA Cells

“…Thus, ATP also potentiated the RVD response, as shown in rat hepatoma cells [59]. In EATC, we found that ATP stimulated PY receptors [60], which resulted in an increase in [Ca 2+ ] i and activation of charybtotoxin-sensitive K + channels. Figure 11 shows that tyrosine phosphorylation plays a central role in the activation of TASK-2 during cell swelling and RVD.…”

Activation of P2Y receptors causes strong and persistent shrinkage of C11-MDCK renal epithelial cells

“…The existing literature suggests that P2Y receptor agonists can modulate cell volume in a cell type-specific manner. Thus ATP was found to produce cell shrinkage in hepatocytes and Ehrlich ascites tumor cells (42,56) but swelling in cultured brain astrocytes (52). Although changes in cell volume may be of physiological significance, particularly for renal epithelial cells, which are exposed to frequent cellvolume changes in anisotonic environments, detailed studies on cell-volume dynamics in response to ATP are lacking.…”

Intracellular Signalling Involved in Volume Regulatory Decrease

“…Provided the external ATP concentration rises high enough during cell swelling, ATP stimulates the P 2 receptors described in EATC [171], resulting a similar potentiation of the RVD response. …”