Control of phospholipase A(2) activity in cockroach (Periplaneta americana) fat body trophocytes by hypertrehalosemic hormone: the role of calcium.
Recently, synthetic HTH-I and HTH-II have been shown to increase the formation of free fatty acids in cockroach (Periplaneta americana) fat body. In this study we show that HTH-II increases PLA(2) activity in dispersed trophocytes, thus implying that phospholipid is a potential source of the fatty acids. The increase in HTH-induced PLA(2) activity is triggered by an increase in [Ca(2+)](i) but extracellular Ca(2+) is also required for a maximal Ca(2+) signal: an effect that can be blocked by the introduction of BAPTA into the trophocytes. Treating trophocytes with ryanodine blocks the increase in PLA(2) activity that follows treatment of the cells with HTH-II. This indicates that the Ca(2+) release channels are distinct from those that respond to inositol trisphosphate. Thapsigargin, which releases Ca(2+) to the cytosol from an intracellular store, increases PLA(2) activity. The data show that the enzyme is translocated from the cytosol to the plasma membrane.
Sun
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Department of Zoology, The University of Western Ontario, London, ON, Canada N6A 5B7.
Steele
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JE
D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005216:Fat Body / Q000166:cytology / Q000201:enzymology; D007301:Insect Hormones / Q000494:pharmacology*; D008297:Male; D009479:Neuropeptides / Q000494:pharmacology*; D010526:Periplaneta / Q000201:enzymology*; D010741:Phospholipases A / Q000378:metabolism*
D000098:Acetophenones; D004791:Enzyme Inhibitors; D007301:Insect Hormones; D009479:Neuropeptides; C043192:glutamyl-valyl-asparaginyl-phenylalanyl-seryl-prolyl-asparaginyl-tryptophanamide; C043191:glutamyl-leucyl-threonyl-phenylalanyl-threonyl-prolyl-asparaginyl-tryptophanamide; D010741:Phospholipases A; C006821:4-bromophenacyl bromide; D002118:Calcium