Ocular hypotensive FP prostaglandin (PG) analogs: PG receptor subtype binding affinities and selectivities, and agonist potencies at FP and other PG receptors in cultured cells.

Natural prostaglandins (PGs) such as PGD2, PGE2, PGF2(2alpha), and PGI2 exhibited the highest affinity for their respective cognate receptors, but were the least selective agents when tested in receptor binding assays. Travoprost acid ([+]-fluprostenol) was the most FP-receptor-selective compound, exhibiting a high affinity (Ki = 35 +/- 5 nM) for the FP receptor, and minimal affinity for DP (Ki = 52,000 nM), EP1 (Ki = 9540 nM), EP3 (Ki = 3501 nM), EP4 (Ki = 41,000 nM), IP (Ki > 90,000 nM), and TP (Ki = 121,000 nM) receptors. Travoprost acid was the most potent PG analog tested in FP receptor functional phosphoinositide turnover assays in the following cell types: human ciliary muscle (EC50 = 1.4 nM), human trabecular meshwork (EC50 = 3.6 nM), and mouse fibroblasts and rat aortic smooth muscle cells (EC50 = 2.6 nM). Although latanoprost acid exhibited a relatively high affinity for the FP receptor (Ki = 98 nM), it had significant functional activity at FP (EC50 = 32-124 nM) and EP1 (EC50 = 119 nM) receptors. Bimatoprost acid was less selective, exhibiting a relatively high affinity for the FP (Ki = 83 nM), EP1 (Ki = 95 nM), and EP3 (Ki = 387 nM) receptors. Bimatoprost acid exhibited functional activity at the EP1 (EC50 = 2.7 nM) and FP (EC50 = 2.8-3.8 nM in most cells) receptors. Bimatoprost (nonhydrolyzed amide) also behaved as an FP agonist at the cloned human FP receptor (EC50 = 681 nM), in h-TM (EC50 = 3245 nM) and other cell types. Unoprostone and S-1033 bound with low affinity (Ki = 5.9 microM to > 22 microM) to the FP receptor, were not selective, but activated the FP receptor. In conclusion, travoprost acid has the highest affinity, the highest FP-receptor-selectivity, and the highest potency at the FP receptor as compared to the other ocular hypotensive PG analogs known so far, including free acids of latanoprost, bimatoprost, and unoprostone isopropyl ester.

Agonist activity of bimatoprost, travoprost, latanoprost, unoprostone isopropyl ester and other prostaglandin analogs at the cloned human ciliary body FP prostaglandin receptor.

We have determined the agonist activity of a number of natural prostaglandins and prostaglandin analogs at the FP prostaglandin receptor cloned from a human ciliary body cDNA library using phosphoinositide (PI) turnover assays. Travoprost acid (EC50 = 3.2 +/- 0.6 nM) was the most potent agonist in these cells followed by bimatoprost free acid (17-phenyl-trinor PGF2alpha; EC50 = 5.8 +/- 2.6 nM), fluprostenol (EC50 = 6.1 +/- 1.5 nM), and latanoprost free acid (PHXA85; EC50 = 54.6 +/- 12.4 nM) which was 17-fold weaker (p < 0.001) than travoprost acid. Unoprostone and S-1033 were significantly (p < 0.001) weaker than travoprost acid. The amide prodrug, bimatoprost (EC50 = 694 +/- 293 nM), activated this FP receptor with an intermediate potency. The isopropyl ester prodrugs, travoprost (EC50 = 42.3 +/- 6.7 nM), latanoprost (EC50 = 126 +/- 347 nM) and unoprostone isopropyl ester (EC50 = 9,100 +/- 2,870 nM), also exhibited FP agonist activity. However, other compounds such as PGI2, bradykinin, histamine, and serotonin were inactive. The agonist activities of bimatoprost, unoprostone (UF-021), fluprostenol and acids of travoprost and latanoprost were antagonized by AL-8810 (11beta-fluoro- 15-epi-15-indanyl-PGF2alpha), an FP-receptor-selective antagonist (Ki = 1.0 - 2.1 microM; n = 3). These studies have demonstrated, for the first time, agonist activities of the currently known and marketed ocular hypotensive prostaglandin analogs at the cloned human ciliary body FP prostaglandin receptor.

Levobetaxolol (Betaxon) and other beta-adrenergic antagonists: preclinical pharmacology, IOP-lowering activity and sites of action in human eyes.

The pharmacological characteristics of levobetaxolol, a single active isomer of betaxolol, were determined and compared with activities of other beta-adrenoceptor antagonists. Levobetaxolol (43-fold beta1-selective) exhibited a higher affinity at cloned human beta1 (Ki = 0.76 nM) than at beta2 (Ki = 32.6 nM) receptors, while dextrobetaxolol was much weaker at both receptors. Levobetaxolol potently antagonized functional activities at cloned human beta1 and beta2 receptors, and also at guinea pig atrial beta1, tracheal beta2 and rat colonic beta3 receptors (IC50s = 33.2 nM, 2970 nM and 709 nM, respectively). Thus, levobetaxolol was 89-times beta1-selective (vs beta2). Levobetaxolol (Ki = 16.4 nM) was more potent than dextrobetaxolol (Ki = 2.97 microM) at inhibiting isoproterenol-induced cAMP production in human non-pigmented ciliary epithelial cells. Levobunolol and (l)-timolol had high affinities at beta1 and beta2 receptors but were considerably less beta1-selective than levobetaxolol. Levo-, dextro- and racemic-betaxolol exhibited little or no affinity, except at sigma sites and Ca2+-channels (IC50s > 1 microM), at 89 other receptor/ligand binding sites. Levobetaxolol exhibited a micromolar affinity for L-type Ca2+-channels. In conscious ocular hypertensive cynomolgus monkeys, levobetaxolol was more potent than dextrobetaxolol, reducing intraocular pressure by 25.9+/-3.2% at a dose of 150 microg/eye (n = 15-30). Quantitative [3H]-levobetaxolol autoradiography revealed high levels of binding to human ciliary processes, iris, choroid/retina, and ciliary muscles. In conclusion, levobetaxolol is a potent, high affinity and beta1-selective IOP-lowering beta-adrenoceptor antagonist.

Functional pharmacological evidence for EP2 and EP4 prostanoid receptors in immortalized human trabecular meshwork and non-pigmented ciliary epithelial cells.

The aim of these studies was to characterize the molecular pharmacology of the prostanoid receptors positively coupled to stimulation of adenylyl cyclase activity in immortalized human trabecular meshwork (TM-3) cells and to compare these results with that of the receptors in immortalized human nonpigmented epithelial (NPE) cells. In general, the TM-3 and NPE cells showed a similar profile with respect to their responses to various prostaglandin (PG) receptor agonists. The rank order of potency (EC50; means +/- SEM) for these compounds in the TM-3 cells was: PGE2 (124 +/- 21 nM) > 13,14-dihydro-PGE1 (430 +/- 110 nM) = PGE1 (522 +/- 345 nM) > 11-deoxy-PGE1 (1063 +/- 118 nM) = 16,16-dimethyl-PGE2 (1776 +/- 460 nM) = butaprost (1920 +/- 527 nM) >> PGD2 = PGI2 = PGF2alpha (n = 3 - 12). While the agonist profile indicated the presence of EP2 receptors, the effects of the EP4 receptor antagonists suggested the additional expression of EP4 receptors in both of these cells. Thus, the EP4 receptor antagonist, AH23848B, at a concentration of 30 microM, caused a dextral shift in the PGE2 concentration-response curves in both TM-3 and NPE cells coupled with a 20-28% decrease in the maximal response of PGE2, indicating apparent noncompetitive antagonism profiles. The antagonist potency of AH23848B in these cells was: Kb = 38.4 +/- 14.8 microM and 23.5 +/- 4.5 microM; -log Kb = 4.7. The other EP4 receptor antagonist, AH22921 (-log Kb = 4.1 - 4.7), was weaker than AH23848B. Taken together, these pharmacological studies have shown than TM-3 and NPE cells apparently contain functional EP2 and EP4 prostanoid receptors positively coupled to adenylyl cyclase.

Pharmacology of functional endogenous IP prostanoid receptors in NCB-20 cells: comparison with binding data from human platelets.

The objective of these studies was to characterize the effects of a broad range of prostanoid agonists upon the stimulation of cAMP production in National Cancer Bank (NCB-20; mouse neuroblastoma/hamster brain hybridoma) cells. The pharmacology of these functional responses in NCB-20 cells was compared with that of the classic endogenous IP receptor present on human platelets using [3H]-iloprost binding techniques. In both assay systems, agonists from the IP prostanoid class exhibited the highest affinities and functional potencies. Specific prostanoids exhibited the following rank order of potency (EC50 +/- SEM) in stimulating cAMP production in the NCB-20 cells: carbaprostacyclin (4.3 +/- 0.9 nM) = PGI2 (6.6 +/-1.5 nM) > iloprost (75+/-13 nM) > 11-deoxy PGE, (378+/-138 nM) > misoprostol (1,243+/-48) > PGE2 (3020+/-700 nM) > ZK-118182 (7265+/-455 nM). Iloprost wasthe most potent compound in the human platelet binding assay while prostanoidsfromthe DPand EP receptor classes showed modest affinity. These studies provide functional and binding information for a broad range of both natural and synthetic prostanoid receptor ligands at the endogenous IP receptor in two different cell types.

Endogenous EP4 prostaglandin receptors coupled positively to adenylyl cyclase in Chinese hamster ovary cells: pharmacological characterization.

The purpose of these studies was to investigate the pharmacology of E-series and selected prostaglandins of other classes on adenylyl cyclase activity in Chinese hamster ovary (CHO) cells expressing an endogenous prostanoid receptor and to compare these responses with those from immortalized human non-pigmented ciliary epithelial (NPE) cells containing the EP2 receptor. 11-deoxy-PGE2 was the most potent of the 16 prostanoid agonists tested for stimulating cAMP formation with a potency (EC50) value of 26 +/- 6 nM in the CHO cells. The endogenous ligand, PGE2, exhibited potencies of 40 +/- 7 nM (n = 24) in the CHO cells and 67 +/- 9 nM (n = 46) in the NPE cells. The EP2 receptor agonist, butaprost, produced an EC50 value of 212 +/- 58 nM (n = 4) in the NPE cells while being inactive (EC50 > 10,000 nM, n = 6) in the CHO cells. The EP4 receptor selective antagonists, AH22921 and AH23848B, at a concentration of 30 microM, caused a 2.2 +/- 0.5 (n = 4) and 8.2 +/- 2.7 (n = 4) fold rightward shift in the PGE2 concentration-response curves in the CHO cells, yielding apparent pKb values of 4.6 +/- 0.6 and 5.3 +/- 0.2 (n = 4), respectively. AH22921 and AH23848B were non-competitive antagonists at the CHO cell EP4 receptor, but did not shift the PGE2 concentration-response curves in the NPE cells containing the EP2 receptor. These studies have characterized the functional prostaglandin receptors in CHO cells pharmacologically and shown them to be consistent with the EP4 subtype.

Affinities, selectivities, potencies, and intrinsic activities of natural and synthetic prostanoids using endogenous receptors: focus on DP class prostanoids.

The prostanoid receptor-subtype binding affinities, selectivities, potencies, and intrinsic activities of four natural prostanoids and six synthetic DP class prostanoids were determined using binding and functional assays with endogenous receptors. SQ27986 exhibited the highest affinity for the human platelet DP receptor and the best DP receptor selectivity profile. Prostaglandin (PG)D(2) was the least DP receptor-selective. The rank order of compound affinities at the DP receptor was SQ27986 (K(i) = 10 +/- 2 nM) > RS93520 = ZK110841 = BW245C (K(i) = 23-26 nM) > ZK118182 (K(i) = 50 +/- 9 nM) > PGD(2) (K(i) = 80 +/- 5 nM). DP receptor agonists produced cAMP in embryonic bovine tracheal fibroblasts with different potencies (EC(50) values in nM): ZK118182 (18 +/- 6), RS93520 (28 +/- 6), SQ27986 (29 +/- 7), ZK110841 (31 +/- 7), BW245C (53 +/- 16), and PGD(2) (98 +/- 10). BW245C was more efficacious and RS93520 was less efficacious than PGD(2). ZK110841 and ZK118182 exhibited a relatively high potency at the adenylyl cyclase-coupled EP(2) receptor in human nonpigmented ciliary epithelial cells but were partial agonists. None of the DP class agonists showed any EP(4) receptor functional activity in Chinese hamster ovary cells. The DP receptor antagonist BWA868C competitively antagonized the PGD(2)-induced cAMP accumulation in embryonic bovine tracheal fibroblast cells (pA(2) = 7.83 +/- 0.08). The dissociation constants for BWA868C antagonizing PGD(2)-, BW245C-, and ZK118182-induced cAMP production were quite similar (apparent -log K(b) = 7.9-8.2, n = 5-9). The pharmacological properties of some natural and numerous DP class synthetic prostanoids have been determined using endogenous receptors.

AL-3138 antagonizes FP prostanoid receptor-mediated inositol phosphates generation: comparison with some purported FP antagonists.

The aim of this study was to pharmacologically characterize the antagonist properties of a novel prostaglandin F2alpha (PGF2alpha) analogue (11-deoxy-16-fluoro PGF2alpha; AL-3138) using a variety of second-messenger assays of prostaglandin receptor subtypes. A detailed comparison was made between AL-3138 and some purported FP receptor antagonists such as PGF2alpha dimethylamine, PGF2alpha dimethylamide, glibenclamide and phloretin using the FP receptor-mediated phosphoinositide turnover assay in A7r5 rat thoracic aorta smooth muscle cells and mouse Swiss 3T3 fibroblasts. The potency and efficacy of AL-3138 as an FP receptor agonist were: EC50 = 72.2 +/- 17.9 nM (Emax = 37%) (n = 3) in A7r5 cells and EC50 = 20.5 +/- 2.8 nM (Emax = 33%) (n = 5) in 3T3 cells. Being a partial agonist, the antagonist potency of AL-3138 against fluprostenol in A7r5 cells was determined to be: Ki = 296 +/- 17 nM (n = 3) and Kb = 182 +/- 44 nM (n = 5) (-log Kb = 6.79 +/- 0.1). AL-3138 exhibited very minimal or no antagonistic effects at EP2, EP4, DP and TP prostaglandin receptors. Both PGF2alpha dimethylamide and PGF2alpha dimethylamine were inactive as FP receptor antagonists, whereas phloretin and glibenclamide were very weak and had -log Kb values of 5.28 +/- 0.09 (n = 3) and 3.58 +/- 0.32 (n = 3), respectively. However, phloretin antagonized functional responses of EP2 and DP prostanoid receptors, and also the V1-vasopressin receptor. AL-3138 competed for [3H]PGF2alpha binding to FP receptors with a relatively high affinity (IC50high = 312 +/- 95 nM) matching its functional antagonist potency. In conclusion, AL-3138 is a more potent and selective FP receptor antagonist than glibenclamide, phloretin, PGF2alpha dimethylamide and PGF2alpha dimethylamine and is therefore a unique and novel pharmacological tool to help characterize FP receptor-mediated functions.

AL-8810: a novel prostaglandin F2 alpha analog with selective antagonist effects at the prostaglandin F2 alpha (FP) receptor.

A novel analog of prostaglandin F(2alpha) [AL-8810; (5Z, 13E)-(9S, 11S,15R)-9,15-dihydroxy-11-fluoro-15-(2-indanyl)-16,17,18,19, 20-pentanor-5,13-prostadienoic acid] has been discovered with uniquely low efficacy (E(max)) at the endogenous prostaglandin F(2alpha) receptors (FP receptors) of A7r5 rat thoracic aorta smooth muscle cells and Swiss mouse 3T3 fibroblasts, as assayed by stimulation of phospholipase C activity. AL-8810 has weak agonist potency (EC(50)) of 261 +/- 44 nM (n = 3) and E(max) = 19% (relative to the full FP receptor agonist cloprostenol) in A7r5 cells and EC(50) of 186 +/- 63 nM (n = 3) and E(max) = 23% in 3T3 fibroblasts. AL-8810 exhibited properties of an apparent competitive antagonist, i.e., produced parallel dextral shifts of the agonist concentration-response curves and no significant suppression of the maximal agonist-induced response, when the potent, selective FP receptor agonist fluprostenol was used. The inhibition parameters of AL-8810 were: pA(2) = 6.68 +/- 0.23 and 6.34 +/- 0.09 (n = 3-4) for A7r5 cells and 3T3 cells, respectively, with Schild slopes ranging from 0.80 to 0.92. AL-8810 concentration-dependently antagonized the response to 100 nM fluprostenol (K(i) = 426 +/- 63 nM; n = 5) in A7r5 cells. However, even at 10 microM concentration, AL-8810 did not significantly inhibit functional responses of TP, DP, EP(2), EP(4), receptor subtypes in various cell lines. AL-8810 also did not antagonize the phospholipase C-coupled V(1)-vasopressin receptor in A7r5 cells. These results suggest that AL-8810 is a unique, selective antagonist at the FP receptor, a heretofore unavailable pharmacological tool that should be valuable for studying FP receptor-mediated functional responses in complex biological systems.

Prostaglandin DP receptors positively coupled to adenylyl cyclase in embryonic bovine tracheal (EBTr) cells: pharmacological characterization using agonists and antagonists.

Various prostaglandin agonists representing various classes of receptor subtypes were evaluated for their ability to stimulate adenylyl cyclase via the endogenous DP receptor in embryonic bovine tracheal (EBTr) cells. Two antagonists were used to block the agonist-induced cyclic AMP production. ZK118182 (EC50 = 16+/-4 nM), RS-93520 (EC50 = 23+/- 4 nM), SQ27986 (EC50 = 33+/-9 nM), ZK110841 (EC50 = 33+/-5 nM), BW245C (EC50 = 59+/-19 nM) and PGD2 (EC50=101+/-10 nM) (n = 4-70) were the most potent agonists. Whilst most compounds were full agonists (Emax = 100% relative to PGD2), BW245C was significantly more efficacious than PGD2 (Emax = 121+/-3%; P<0.001) and RS-93520 appeared to be a partial agonist (Emax = 64+/-9%; P<0.001). Agonists from the EP (e.g. enprostil; misoprostol; butaprost), FP (e.g. cloprostenol; fluprostenol; PHXA85), IP (iloprost; PGI2) and TP (U46619) prostanoid receptor classes were weak agonists or inactive in the EBTr cell assay system. The DP-receptor antagonist, BWA868C, showed a competitive antagonist profile with pA2 values of 8.00+/-0.02 and 8.14+/-0.13 in Schild analyses with two structurally different agonists, BW245C and ZK118182, respectively (n = 3). AH6809, another purported DP-receptor antagonist, weakly inhibited PGD2- and ZK 18182-induced cyclic AMP production (K(i)s = 808+/-193 nM and 782+/-178 nM, respectively). The current studies have characterized the DP receptor positively coupled to adenylyl cyclase in EBTr cells using a wide range of agonist and antagonist prostaglandins. These data support the utility of the EBTr cell line as a useful tool for the evaluation of DP receptor agonists and antagonists and for profiling other classes of prostaglandins.

Use of a semi-automated, robotic radioimmunoassay to measure cAMP generated by activation of DP-, EP2-, and IP-prostaglandin receptors in human ocular and other cell types.

The aim of these studies was to compare the effects of several prostaglandin agonists on adenylyl cyclase activity in embryonic bovine tracheal (EBTr) cells, transformed human nonpigmented ciliary epithelial (NPE) cells and National Cancer Bank (NCB-20) cells. These cell types have been shown to express DP, EP2 and IP prostaglandin (PG) receptors, respectively. Cyclic AMP (cAMP) generation was measured by manual and semi-automated radioimmunoassay (RIA) techniques. ZK118182 (EC50 = 10-27 nM), PGE2 (EC50 = 21-27 nM) and PGI2 (EC50 = 3.5-4 nM) had the highest potency at the DP, EP2 and IP receptors, respectively. A plot of potency (EC50) values generated with both techniques showed a high degree of correlation for all three receptors. These studies provide further characterization of prostanoid receptor functional responses in three cell types and demonstrate the advantages of a semi-automated RIA method for the analysis of the second messenger cAMP.

Prostaglandin-stimulated adenylyl cyclase activity via a pharmacologically defined EP2 receptor in human nonpigmented ciliary epithelial cells.

The goal of these studies was to compare the effects of several prostaglandin (PG) receptor agonists on adenylyl cyclase activity in transformed human nonpigmented ciliary epithelial (NPE) cells. In order to define the pharmacology of the PG receptors present on these cells, cyclic AMP production was measured by both manual and robotic radioimmunoassay (RIA) techniques. In NPE cells, the rank order of potency for the PGs tested in the current study (n = up to 46) was PGE2 (EC50 = 67 nM) > 13,14-dihydro-PGE1 (EC50 = 231 nM) > 11-deoxy-PGE1 (EC50 = 500 nM) = 16,16-dimethyl-PGE2 (EC50 = 872 nM) = 11-deoxy-16,16-dimethyl-PGE2 (EC50 = 1135 nM) >> PGF2 alpha (EC50 > 10,000 nM) = PGD2 (EC50 > 10,000 nM) = PGI2 (EC50 > 10,000 nM). The EP2-receptor selective PG, butaprost, exhibited a potency of 212 nM (Emax = 55%). The response to 1 microM PGE2 was antagonized by AH6809 (IC50 = approximately 50 microM, Kb = 4 microM). The relative potencies of the EP agonists mentioned above were significantly weaker in EbTr and NCB-20 cells expressing DP and IP receptors, respectively (1). These data provide a detailed pharmacological identification and characterization of EP2 receptors on NPE cells.

Pharmacology of [3H]prostaglandin E1/[3H]prostaglandin E2 and [3H]prostaglandin F2alpha binding to EP3 and FP prostaglandin receptor binding sites in bovine corpus luteum: characterization and correlation with functional data.

Specific binding of [3H]prostaglandin (PG) E1, [3H]PGE2 and [3H]PGF2alpha to washed total particulate homogenates of bovine corpus luteum comprised 60 to 82% of total binding. Scatchard analysis of competition data revealed the presence of an apparent single population of binding sites for [3H]PGE1 and [3H]PGE2 with dissociation constants (Kds) of 2.76 to 3.39 nM and apparent receptor density (Bmax) of 1.5 to 1.56 pmol/g wet weight (n = 3-4). However, [3H]PGF2alpha appeared to interact with two classes/states of binding sites (Kd1 = 6.51 +/- 0.65 nM, Bmax1 = 2.33 +/- 0.26 pmol/g wet weight; Kd2 = 986 +/- 269 nM; Bmax2 = 44.8 +/- 11.3 pmol/g wet weight, n = 11). Specific [3H]PGE1 and [3H]PGE2 binding was most potently (nanomolar affinity) inhibited by PGs with high selectivity for the EP3 receptor subtype (e.g., GR63799, sulprostone, enprostil) but was weakly (Kis > 1 microM) influenced by EP1-selective (SC-19220), FP-selective (fluprostenol, PHXA85), DP-selective (BWA868C; ZK118182), IP-selective (iloprost) and TP-selective (U46619) PGs. Specific [3H]PGF2alpha binding was potently displaced by FP-selective agents such as fluprostenol, PHXA85 and cloprostenol with nanomolar affinities (n = 3-25), but weakly (Kis > 1 microM) by other PGs showing high selectivity for other PG receptor subtypes mentioned above. The relative specificities and potencies of EP3- and FP-selective PGs tested in the binding assays were confirmed using various functional assays. These studies have provided strong pharmacological evidence for the similarity of [3H]PGE1 and [3H]PGE2 binding to EP3 receptors and for [3H]PGF2alpha binding to FP receptors in washed bovine corpus luteum homogenates.

Pharmacological analysis of mast cell mediator and neurotransmitter receptors coupled to adenylate cyclase and phospholipase C on immunocytochemically-defined human conjunctival epithelial cells.

We sought to establish and immunocytochemically characterize primary cultures of human conjunctival epithelial (HCE) cells, and to determine the types of receptors coupled to adenylate cyclase (AC) and phospholipase C (PLC) present on them which may be stimulated following allergic or inflammatory provocation of the tissue. HCE cells possessed the key epithelial cell surface cytokeratins AE1, AE3 and AE5. Signal transduction studies (n > or = 3), using agonists and antagonists, revealed the presence of beta 2-adrenergic (isoproterenol EC50 = 5.2 nM), prostaglandin E2 (EC50 = 168 nM) and vasoactive intestinal peptide (EC50 = 0.69 nM) receptors positively coupled to AC in HCE cells. Bradykinin (EC50 = 0.83 nM), platelet activating factor (EC50 = 4.5 nM), leukotriene C4 (EC50 = 300 nM) and histamine1 (EC50 = 3.1 microM) receptors were coupled to PLC (n = 3 for each). These data suggest that HCE cells in vivo may represent target cells for mast cell mediators and certain neurotransmitters which are released into the tear-film upon allergic provocation of the conjunctiva.

The effects of elevated glucose on Na+/K(+)-ATPase of cultured bovine retinal pigment epithelial cells measured by a new nonradioactive rubidium uptake assay.

The effects of stimulated hyperglycemia on the Na+/K(+)-ATPase activity of cultured bovine retinal pigment epithelial (RPE) cells were investigated. Total Rb+ uptake, measured by a chromatographic method, was decreased 20-30% by 55.5 mM glucose relative to 5.55 mM glucose for culture periods of 2 to 28 days. An acute hyperglycemic stress (< 1 week) had no effect on ouabain-inhibition of Rb+ uptake or ouabain binding to RPE cells (IC50 = 55 nM for both processes) and did not alter the IC50 value (near 10 nM) for binding of strophanthidin, another selective Na+/K(+)-ATPase inhibitor. A small increase in the apparent K(m) of Rb+ for Na+/K(+)-ATPase accompanied the decrease in maximal Rb+ uptake at 55.5 mM glucose. The continuous presence of AL-1576, an aldose reductase inhibitor (ARI), normalized the effect of severe hyperglycemia on Rb+ uptake in the chronic (28 days) but not the acute exposure protocols. Thus, decreased efficiency of Na+/K(+)-ATPase caused by chronic accumulation of intracellular sorbitol can account for previously reported functional and structural alterations in the RPE cell layer of diabetic rodents. The results of the present study suggest that hyperglycemia-induced loss of Na+/K(+)-ATPase function in RPE cells, which responds to aldose reductase inhibitor treatment, contributes to the pathogenesis of diabetic retinopathy.

FP prostaglandin receptors mediating inositol phosphates generation and calcium mobilization in Swiss 3T3 cells: a pharmacological study.

A detailed pharmacological characterization of the prostaglandin (PG) receptor coupled to phosphoinositide (PI) turnover and intracellular calcium mobilization in Swiss 3T3 mouse fibroblast cells was undertaken. The pharmacological profile of this functional receptor was compared with the pharmacological profile of specific [3H]PGF2 alpha binding to bovine corpus luteum membranes, which are known to contain a bona fide FP receptor. PGs that were potent stimulators and full agonists in the PI turnover assay in the 3T3 cells were the following (for all, n = 3-45): 16-phenoxy-PGF2 alpha (EC50 = 0.61 +/- 0.1 nM), cloprostenol (EC50 = 0.73 +/- 0.04 nM), 17-phenyl-PGF2 alpha (EC50 = 2.71 +/- 0.35 nM), fluprostenol (EC50 = 3.67 +/- 0.61 nM), PhXA85 (EC50 = 27.3 +/- 5.63 nM) and PGF2 alpha (EC50 = 28.5 +/- 5.26 nM). However, PGD2 (EC50 = 155 +/- 29.9 nM; Emax = 49% of cloprostenol), PGE2 (EC50 = 2570 +/- 566 nM; Emax = 59%) and U46619 (EC50 = 1060 +/- 310 nM; Emax = 63%) were less potent and were partial agonists, and iloprost and BW245C were inactive. Although the PGs tested exhibited lower affinities in the 3[H]PGF2 alpha binding assay than their functional potencies in the PI turnover assay, the rank orders of potencies and affinities were well correlated (r = 0.94; n = 15 compounds). However, the PI turnover assay was more sensitive than the calcium mobilization assay for rank ordering PG agonists. In conclusion, the Swiss 3T3 cells express an FP receptor coupled to PI turnover and intracellular Ca+2 mobilization signal transduction pathways. The pharmacological profile of this receptor was similar to that of the FP receptor found in the bovine corpus luteum, a tissue previously used to clone the first pharmacologically defined FP receptor.

A new chromatographic method for measurement of rubidium transport activities in cultured bovine retinal pigment epithelial cells.

A new method for measuring cellular rubidium (Rb+) uptake activities based on cation chromatography was developed and compared with the standard technique, uptake of the radioisotope 86Rb+, using cultured bovine retinal pigment epithelial (RPE) cells. The Rb+ response was strictly linear from 0.25 nmol (detection limit) to 25 nmol. The Na+/K(+)-ATPase inhibitor ouabain inhibited Rb+ uptake with IC50 values of 128.7 +/- 23.5 nM (n = 8; radioactive method) and 56.6 +/- 9.3 nM (n = 9; non-radioactive method, p < 0.01). The latter value is identical to the IC50 value of 54.4 +/- 16.2 nM (n = 3) for ouabain binding to the intact RPE cells. Ouabain and bumetanide, an inhibitor of the Na+/K+/Cl(-)-cotransporter, each inhibited Rb+ uptake maximally by 66 and 30%, respectively. This new technique allows sensitive measurement of intracellular Rb+, as well as K+ and Na+, and, thus, should prove useful for studying the effects of pharmacologic agents and simulated disease conditions on cation transport and cation balance in RPE and other cell types.