15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and 2--7--bis(carboxyethyl)-5(6)-carboxyfluorescein

Prostaglandins (PG) and thromboxane A2 (TxA2) have marked vasoactive effects on the renal glomerular microcirculation. Exposure of cultured mesangial cells to PGF2 alpha and TxA2 mimetics results in a rapid elevation of free cytosolic Ca2+ ([Ca2+]i) followed by contraction and cell proliferation. We studied whether other ionic changes mediate these effects of eicosanoids on cells of rat and human origin. Cytoplasmic pH (pHi) was monitored in cells loaded with the fluorescent, intracellularly trapped pH-sensitive probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. PGF2 alpha in rat cells and the TxA2 mimetic U-46619 in human cells induced rapid, dose-dependent cytosolic acidification followed by recovery and net alkalinization mediated by enhanced Na(+)-H+ exchange. The early acidification was also stimulated by ionomycin and Ca2(+)-mobilizing peptides, implicating a Ca2(+)-dependent mechanism. Alkalinization was abolished by removal of extracellular Na+ and by amiloride. Both components of the responses were inhibited by phorbol myristate acetate, which could mimic alkalinization, suggesting a regulatory role of protein kinase C in activation of the Na(+)-H+ exchanger by eicosanoids. Vasoconstrictor arachidonate metabolites may control glomerular cell function by a signaling mechanism centered on concurrent changes of pHi and [Ca2+]i.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Arginine Vasopressin; Calcium; Cell Line; Cells, Cultured; Cytosol; Dinoprost; Fluoresceins; Fluorescent Dyes; Glomerular Mesangium; Humans; Hydrogen-Ion Concentration; Ionomycin; Kinetics; Male; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Inbred Strains; Tetradecanoylphorbol Acetate; Thromboxane A2

The effects of arachidonic acid and thrombin on calcium movements have been studied in fura-2-loaded platelets by a procedure which allows simultaneous monitoring of the uptake of manganese, a calcium surrogate for Ca2+ channels, and the release of Ca2+ from intracellular stores. Arachidonic acid induced both Ca2+ (Mn2+) entry through the plasma membrane and Ca2+ release from the intracellular stores. The release of Ca2+ was prevented by cyclo-oxygenase inhibitors and mimicked by the prostaglandin H2/thromboxane A2 receptor agonist U46619. Ca2+ (Mn2+) entry required higher concentrations of arachidonic acid and was not prevented by either cyclo-oxygenase or lipoxygenase inhibitors. Several polyunsaturated fatty acids reproduced the effect of arachidonic acid on Ca2+ (Mn2+) entry, but higher concentrations were required. The effects of maximal concentrations of arachidonic acid and thrombin on the uptake of Mn2+ were not additive. Both agonists induced the entry of Ca2+, Mn2+, Co2+ and Ba2+, but not Ni2+, which, in addition, blocked the entry of the other divalent cations. However, arachidonic acid, but not thrombin, increased a Ni2(+)-sensitive permeability to Mg2+. The effect of thrombin but not that of arachidonic acid was prevented either by pretreatment with phorbol ester or by an increase in cyclic-AMP levels. Arachidonic acid also accelerated the uptake of Mn2+ by human neutrophils, rat thymocytes and Ehrlich ascites-tumour cells.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyrazol-3-amine; Animals; Arachidonic Acid; Arachidonic Acids; Aspirin; Biological Transport; Blood Platelets; Calcium; Carcinoma, Ehrlich Tumor; Egtazic Acid; Fatty Acids, Nonesterified; Fatty Acids, Unsaturated; Fluoresceins; Fluorescent Dyes; Fura-2; Humans; In Vitro Techniques; Kinetics; Manganese; Masoprocol; Mice; Neutrophils; Prostaglandin Endoperoxides, Synthetic; Rats; Spectrometry, Fluorescence; Structure-Activity Relationship; T-Lymphocytes; Thrombin