6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2h-pyran-2-one and 4-bromophenacyl-bromide

Previously, we reported that emptying of intracellular Ca(2+) pools with endoplasmatic Ca(2+)-ATP-ase inhibitor thapsigargin leads to the Na(+) influx in human lymphocytes (M. Tepel et al., 1994, J. Biol. Chem. 269, 26239-26242). In the present study we examined the mechanism underlying the thapsigargin-induced Na(+) entry. We found that the thapsigargin-induced increase in Na(+) concentration was effectively inhibited by three structurally unrelated phospholipase A(2) (PLA(2)) inhibitors, p-bromophenacyl bromide, 3-(4-octadecyl)-benzoylacrylic acid (OBAA), and bromoenol lactone (BEL). The thapsigargin-induced Na(+) influx could be mimicked by PLA(2) exogenously added to the lymphocyte suspension. In addition, thapsigargin stimulated formation of arachidonic acid (AA), the physiological PLA(2) product. AA induced Na(+) entry in a time- and concentration-dependent fashion. Both, thapsigargin-induced Na(+) influx and AA liberation were completely inhibited in the presence of tyrosine kinase inhibitor genistein but not in the absence of extracellular Ca(2+). Collectively, these data show that thapsigargin-induced Na(+) entry is associated with tyrosine kinase-dependent stimulation of PLA(2).

Topics: Acetophenones; Acrylates; Arachidonic Acid; Benzoates; Cell Membrane; Clotrimazole; Econazole; Humans; In Vitro Techniques; Indomethacin; Kinetics; Lymphocytes; Masoprocol; Naphthalenes; Phosphodiesterase Inhibitors; Phospholipases A; Pyrones; Sodium; Thapsigargin

The participation of phospholipase A2 isoforms in capacitative store-operated Ca2+ influx into Jurkat leukemic T and MDCK cells was investigated. Preincubation of Jurkat cells with either bromophenacyl bromide (an inhibitor of secreted phospholipase A2, sPLA2) or Helss (an inhibitor of calcium independent phospholipase A2--iPLA2) resulted in a significant inhibition of the calcium influx. The extent of this inhibition depended on the pH of the extracellular millieu; it increased with alkalisation. The rate of Ca2+ influx into MDCK cells was reduced by bromophenacyl bromide. Preincubation of these cells with Helss resulted in the stimulation of the influx. These observations suggest the participation of different PLA2 isoforms in the regulation of Ca2+ influx. They also show that the extent that PLA2 isoforms control the influx depends on the pH of the medium. Finally, these data indicate that various phospholipase A2 isoforms may play a role in the control of Ca2+ influx in different cell lines.

Topics: Acetophenones; Animals; Calcium; Calcium Signaling; Cell Line; Dogs; Electrophysiology; Enzyme Inhibitors; Humans; Hydrogen-Ion Concentration; Ion Transport; Isoenzymes; Jurkat Cells; Kinetics; Naphthalenes; Phospholipases A; Phospholipases A2; Pyrones