Glaucoma patients present increased levels of diadenosine tetraphosphate, Ap(4)A, in the aqueous humour.

Previous studies have shown the presence of diadenosine tetraphosphate (Ap(4)A) and pentaphosphate (Ap(5)A) in the aqueous humour (AH) of different species. When topically applied to the rabbit cornea, Ap(4)A decreased IOP while Ap(5)A increased it. Here we study the presence of dinucleoside polyphosphates in the AH from human patients with or without glaucoma. AH was obtained at the time of cataract surgery from patients with (n=16) or without (n=10) primary open-angle glaucoma. AH (0.1-0.2 ml) was collected at the beginning of surgery through a corneal paracentesis and immediately cooled in liquid nitrogen, kept frozen and protected from light. AH aliquots were analyzed by HPLC for the presence of Ap(4)A and Ap(5)A. Both, Ap(4)A and Ap(5)A were detected in the AH of both experimental groups. No significant differences were found for Ap(5)A. In contrast, Ap(4)A levels were increased by ∼15-fold in the AH from glaucomatous eyes ranging from 19.5±9.2 nM in normal individuals to 286.03±30.9 nM in glaucomatous patients. In conclusion, both Ap(4)A and Ap(5)A were detected for the first time in human AH. Interestingly, glaucomatous eyes presented elevated concentrations of Ap(4)A compared to controls. The role of Ap(4)A needs to be elucidated but it may help to protect the autonomic innervation in the ciliary body/trabecular meshwork. Also, because of its higher levels in glaucoma patients it may be considered as a possible glaucoma biomarker.

Profilin induces lamellipodia by growth factor-independent mechanism.

Profilin has been implicated in cell motility and in a variety of cellular processes, such as membrane extension, endocytosis, and formation of focal complexes. In vivo, profilin replenish the pool of ATP-actin monomers by increasing the rate of nucleotide exchange of ADP-actin for ATP-actin, promoting the incorporation of new actin monomers at the barbed end of actin filaments. For this report, we generated a membrane-permeable version of profilin I (PTD4-PfnI) for the alteration of intracellular profilin levels taking advantage of the protein transduction technique. We show that profilin I induces lamellipodia formation independently of growth factor presence in primary bovine trabecular meshwork (BTM) cells. The effects are time- and concentration-dependent and specific to the profilin I isoform. Profilin II, the neuronal isoform, failed to extend lamellipodia in the same degree as profilin I. H133S, a mutation in the polyproline binding domain, showed a reduced ability to induce lamellipodia. H199E, mutation in the actin binding domain failed to induce membrane spreading and inhibit fetal bovine serum (FBS) -induced lamellipodia extension. Incubation with a synthetic polyproline domain peptide (GP5)3, fused to a transduction domain, abolished lamellipodia induction by profilin or FBS. Time-lapse microscopy confirmed the effects of profilin on lamellipodia extension with a higher spreading velocity than FBS. PTD4-Pfn I was found in the inner lamellipodia domain, at the membrane leading edge where it colocalizes with endogenous profilin. While FBS-induced lamellipodia formation activates Rac1, PTD4-Pfn I stimulation did not induce Rac1 activation. We propose a role of profilin I favoring lamellipodia formation by a mechanism downstream of growth factor.

Activation of store-operated Ca(2+) channels in trabecular meshwork cells.

PURPOSE: In nonexcitable cells, G(q)-coupled membrane receptor activation induces a biphasic increase in intracellular calcium ([Ca(2+)](i)) expressed as an initial IP(3)-dependent release from intracellular stores followed by a sustained Ca(2+) influx from the extracellular space that involves store-operated Ca(2+) channels (SOCs). In trabecular meshwork (TM) cells, contractile agonists such as bradykinin (BK) and endothelin-1 (ET-1) induce this type of Ca(2+) signaling. Given that trabecular outflow is modified by tissue contractility, the authors characterized SOCs and studied their participation in TM cell contractility. METHODS: [Ca(2+)](i) was measured in cultured bovine TM cells loaded with Fura-2. Ca(2+) currents were recorded using the patch clamp technique. Cell contractility measurements were assessed by traction microscopy. RESULTS: BK and ET-1 activate a store-operated Ca(2+) entry that was greatly reduced in the absence of extracellular Ca(2+) or by preincubation with SOC blocker 2-APB or SKF96365. Store-operated Ca(2+) currents were also activated by intracellular dialysis with IP(3) + EGTA or after stimulation with thapsigargin. Electrophysiological characterization supports the presence of Ca(2+) release-activated Ca(2+) channels (CRACs) and nonselective cation channels, of which TRPC1 and TRPC4 channels may be candidate TRPs detected in TM cells. Extracellular Ca(2+) entry through SOCs is not required for TM cell contraction in response to BK or ET-1, but it modulates this process. CONCLUSIONS: Extracellular Ca(2+) entry in TM cells in response to agonist stimulation and store-depletion is mediated by the activation of SOCs, which do not contribute to cell contraction but which may activate regulatory mechanisms to prevent excessive contraction. CRAC and TRPC channels involved represent interesting modulators of TM function to improve aqueous humor outflow.

Medical education in Spain: current status and new challenges.

As in other countries, medical education in Spain is structured across three distinct stages: undergraduate or basic medical education; postgraduate specialized training; and continuing medical education. The aim of this article is to give an overview of the current state of these three stages, discussing the strengths and weaknesses and the challenges facing each one in the coming years, and how Spain can look to the international community to support change. We suggest that the undergraduate medical education system should be adapted to Spain's new social requirements and requires to be increasingly aligned with postgraduate training. We suggest that continuing medical education should develop its Continuous Professional Development programmes to ensure the permanent competence of Spanish medical professionals. The European Higher Education arena, as defined by the Bologna Declaration, provides many opportunities as well as a challenging situation for improving any current weaknesses in the Spanish medical education system.

Acquisition of learning outcomes by students from the Medical School of the University of Barcelona (Catalonia, Spain): a student survey.

BACKGROUND: In 2001, in order to improve the curriculum, the medical school of the University of Barcelona began discussions aimed at defining specific learning outcomes for its medical graduates and, subsequently, evaluating the acquisition of these competencies. AIM: To report the views of our medical students regarding the extent to which they have acquired the learning outcomes previously defined by the faculty. METHOD: A questionnaire was administered to seventy final year students, who had finished all the course clerkships and they were asked to indicate on a Likert scale their perceived level of acquisition of each learning outcome. RESULTS: Overall, the students report an adequate level of competency and consider themselves able to meet skills targets under supervision in eight of the eleven domains investigated. In three of the domains (patient management, medical information search skills, and decision-making skills and clinical reasoning and judgment) students regarded themselves as only partially competent. These results agree with the global course score of the students, according to the medical school assessment system. CONCLUSIONS: The results will allow us to make curricular and methodological changes in order to implement a new outcome-based curriculum.

Pyrethroids inhibit K2P channels and activate sensory neurons: basis of insecticide-induced paraesthesias.

Pyrethroid insecticides are widely used for pest control in agriculture or in human public health commonly as a topical treatment for scabies and head lice. Exposure to pyrethroids such as permethrin or tetramethrin (TM) causes sensory alterations such as transient pain, burning, stinging sensations, and paraesthesias. Despite the well-known effects of pyrethroids on sodium channels, actions on other channels that control sensory neuron excitability are less studied. Given the role of 2-pore domain potassium (K2P) channels in modulating sensory neuron excitability and firing, both in physiological and pathological conditions, we examined the effect of pyrethroids on K2P channels mainly expressed in sensory neurons. Through electrophysiological and calcium imaging experiments, we show that a high percentage of TM-responding neurons were nociceptors, which were also activated by TRPA1 and/or TRPV1 agonists. This pyrethroid also activated and enhanced the excitability of peripheral saphenous nerve fibers. Pyrethroids produced a significant inhibition of native TRESK, TRAAK, TREK-1, and TREK-2 currents. Similar effects were found in transfected HEK293 cells. At the behavioral level, intradermal TM injection in the mouse paw produced nocifensive responses and caused mechanical allodynia, demonstrating that the effects seen on nociceptors in culture lead to pain-associated behaviors in vivo. In TRESK knockout mice, pain-associated behaviors elicited by TM were enhanced, providing further evidence for a role of this channel in preventing excessive neuronal activation. Our results indicate that inhibition of K2P channels facilitates sensory neuron activation and increases their excitability. These effects contribute to the generation of paraesthesias and pain after pyrethroid exposure.

Use of transduction proteins to target trabecular meshwork cells: outflow modulation by profilin I.

PURPOSE: Fusion proteins containing a protein transduction domain (PTD4) are able to cross biological membranes. We tested the applicability of the protein transduction method for study of the aqueous humor trabecular outflow pathway by targeting the actin cytoskeleton, which is known to be involved in outflow facility regulation. METHODS: Expression vectors useful for generating fusion proteins with the PTD4 domain and the actin-binding protein Profilin I were constructed. The transductional and functional properties of these proteins were tested in bovine trabecular meshwork cells in culture. The effects of PTD4-Profilin I on outflow facility were evaluated in perfused bovine anterior segments. PTD4-beta-galactosidase was used to visually check correct delivery of fusion proteins to trabecular meshwork cells. RESULTS: The fusion proteins generated were characterized by western blot. Immunocytochemistry experiments showed intracellular staining for PTD4-Profilin I in trabecular meshwork cells in culture. The fusion protein was found in the cytoplasm associated with actin filaments and in the leading edge of the cellular membrane. In contrast, control Profilin I, without the PTD4 domain, was unable to cross the cell membrane. In perfused anterior segments, 2 microM PTD4-Profilin I increased trabecular outflow facility in a reversible manner, while Profilin I had no significant effect. Anterior segments perfused with PTD4-beta-galactosidase showed positive staining in the trabecular meshwork tissue. CONCLUSIONS: Protein transduction technology is a valuable tool for targeting trabecular meshwork tissue, not only for performing physiological studies, but also as a potential drug-delivery method. Profilin I action on the actin cytoskeleton further reinforces the importance of this structure in outflow facility regulation.

Educational climate perception by preclinical and clinical medical students in five Spanish medical schools.

OBJECTIVE: The purpose of this study was to investigate student's perceptions of Educational Climate (EC) in Spanish medical schools, comparing various aspects of EC between the 2nd (preclinical) and the 4th (clinical) years to detect strengths and weaknesses in the on-going curricular reform. METHODS: This study utilized a cross-sectional design and employed the Spanish version of the "Dundee Ready Education Environment Measure" (DREEM). The survey involved 894 2nd year students and 619 4th year students from five Spanish medical schools. RESULTS: The global average score of 2nd year students from the five medical schools was found to be significantly higher (116.2±24.9, 58.2% of maximum score) than that observed in 4th year students (104.8±29.5, 52.4% of maximum score). When the results in each medical school were analysed separately, the scores obtained in the 2nd year were almost always significantly higher than in the 4th year for all medical schools, in both the global scales and the different subscales. CONCLUSIONS: The perception of the EC by 2nd and 4th year students from five Spanish medical schools is more positive than negative although it is significantly lower in the 4th year. In both years, although more evident in the 4th year, students point out the existence of several important "problematic educational areas" associated with the persistence of traditional curricula and teaching methodologies. Our findings of this study should lead medical schools to make a serious reflection and drive the implementation of the necessary changes required to improve teaching, especially during the clinical period.

Acid-sensing ion channels detect moderate acidifications to induce ocular pain.

Sensory nerve fibers innervating the ocular anterior surface detect external stimuli producing innocuous and painful sensations. Protons are among the first mediators released by damaged cells during inflammation, tissue injury, or other chronic ophthalmic conditions. We studied whether acid-sensing ion channels (ASICs) are expressed in corneal sensory neurons and their roles in the response to moderate acidifications of the ocular surface and in pathologies producing ocular surface inflammation. Moderate acidic pH (6.6) activated ASIC-like currents in corneal sensory neurons, which were blocked by ASIC1- or ASIC3-specific toxins. Acidic pH depolarizes corneal sensory neurons to fire action potentials, an effect blocked by the ASIC3 inhibitor APETx2. 2-Guanidino-4-methylquinazoline, an ASIC3 agonist, activated a population of corneal polymodal sensory nerve fibers and significantly increased the blinking and tearing rate. The nocifensive behaviors produced by application of either a moderate acidic stimulus or ophthalmic drugs formulated in acidic solution were abolished by ASIC blockers. In a model of allergic keratoconjunctivitis, nocifensive behavior was greatly reduced by ASIC3 blockade, presumably by reducing nociceptor sensitization during the inflammatory process. Our results show that, in addition to the established role of TRPV1, ASICs play a significant role in the detection of acidic insults at the ocular surface. The identification of ASICs in corneal neurons and their alterations during different diseases is critical for the understanding of sensory ocular pathophysiology. They are likely to mediate some of the discomfort sensations accompanying several ophthalmic formulations and may represent novel targets for the development of new therapeutics for ocular pathologies.

Cell membrane stretch modulates the high-conductance Ca2+-activated K+ channel in bovine trabecular meshwork cells.

PURPOSE: Anterior chamber structures are subjected to changes in intraocular pressure (IOP). Several studies have pointed out that trabecular meshwork (TM) cells are sensitive to mechanical stretch and that cell-signaling mechanisms are activated in response to elevated pressure. Because membrane stretch has been shown to be a modulator of several ionic conductances, this study was conducted to determine its effects on the high-conductance Ca(2+)-activated K(+) (BK(Ca)) channels present in TM cells. METHODS: Primary cultures of TM cells from bovine eyes were used. Patch-clamp recordings were performed in the cell-attached, inside-out, and whole-cell configurations. To stretch the cell membrane, both suction to the rear end of the patch pipette and hypotonic shock were used. Intracellular calcium concentration ([Ca(2+)](i)) was measured in TM cells loaded with fura-2, using an epifluorescence microscope coupled to a charge-coupled device (CCD) camera. RESULTS: Electrophysiological characterization of BK(Ca) channels was in agreement with previous studies. In cell-attached patches, the open probability of the BK(Ca) channel (i.e., the amount of time the channel is open) increased consistently when 14- to 45-mm Hg suctions were applied at a constant depolarized voltage. At a constant pressure (25 or 45 mm Hg), channel openings increased when depolarizing pulses were applied to the patch. Stretch activation of the BK(Ca) channel was not mediated by increases in [Ca(2+)](i), because it was present in inside-out patches maintained at a constant Ca(2+) concentration. Nevertheless, it cannot be ruled out that at low suction levels, a minimum Ca(2+) concentration is necessary for channel activation. Whole-cell currents carried by BK(Ca) channels increased when the isotonic solution in the bath was exchanged with a hypotonic solution and were selectively blocked by iberiotoxin. In our conditions, the hypotonic shock did not modify [Ca(2+)](i). CONCLUSIONS: The data show that in TM cells, open probability of the BK(Ca) channel is enhanced by membrane stretching as well as by membrane depolarization and [Ca(2+)](i). Changes in membrane tension induced by cell volume increase also activated whole-cell BK(Ca) currents. Homeostatic mechanisms in TM cells may involve BK(Ca) channel activation in response either to changes in cell volume or changes in IOP.

Modulation of aqueous humor outflow by ionic mechanisms involved in trabecular meshwork cell volume regulation.

PURPOSE: Trabecular meshwork (TM) cell shape, volume, contractility and their interactions with extracellular matrix determine outflow facility. Because cell volume seems essential to TM function, this study was conducted to investigate further the ionic channels and receptors involved in regulatory volume decrease and their roles in modulating outflow facility. METHODS: Primary cultures of bovine TM cells were used. K(+) and Cl(-) currents were studied with whole-cell patch clamping. Swelling was induced by hypotonic shock. [Ca(2+)](i) was measured in TM cells loaded with fura-2. Bovine anterior segments were perfused at constant pressure to measure outflow facility. RESULTS: Hypotonic media activated both the high-conductance Ca(2+)-activated K(+) channel (BK(Ca)) and swelling-activated Cl(-) channel (Cl(swell)) currents and induced release of adenosine 5'-triphosphate (ATP) from TM cells. ATP activated P2Y(2) receptors with the following profile: ATP = uridine 5'-triphosphate (UTP) > adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma S) > adenosine 5'-diphosphate (ADP) = uridine 5'-diphosphate (UDP), and increased BK(Ca) current. Hypotonic medium initially decreased outflow facility in perfused anterior segments, which recovered with time to baseline levels. Addition of tamoxifen or iberiotoxin (Cl(swell) and BK(Ca) blockers, respectively) lengthened the recovery phase, which implies that these channels participate in cell volume regulation. In contrast, an activator of BK(Ca)s (NS1619) produced the opposite effect. CONCLUSIONS: Cell swelling activates a regulatory volume decrease mechanism that implies activation of K(+) and Cl(-) currents and participation of P2Y(2) receptors. Because previous studies have shown that intracellular volume of TM cells is an important determinant of outflow facility, it seems feasible that cell volume regulation would be part of the homeostatic mechanisms of the TM, to regulate the outflow pathway.

[The White Paper of the health professions of Catalonia]. / Le livre Blanc des Professions de Santé de Catalogne.

The White Paper of the Health Professions of Catalonia (WPHPC) is a strategic document for the development of the health professions. It deals with the main components of the manpower development (education, management and planning) in relation to the health services development required to attain the objectives defined in the Catalan Health Plan. The WPHPC fosters the coherence between social needs and professional competencies required to respond to them, as well as to the quantitative aspects of service needs under adequate standards of quality, effectiveness and efficiency. The WPHPC has followed a methodological process with maximum stakeholder participation and transparency. Citizens, professionals and health organizations have contributed significantly. The conclusions and recommendations of the WPHPC are organized around four axis: the citizenship, the professionals, the health care organizations and the health care model. Key elements are: the requirement of a new social contract between the different stakeholders, the values of professionalism, the need for a new credentialism of professional competencies, innovation in the education process, innovation of governance and management for organization of knowledge, the redistribution of work inside teams requires deregulation and reregulation of the professions, the need for actualized data on workforce and job positions and the permanent requirement of sociological research.

Effects of platelet-derived growth factor on aqueous humor dynamics.

PURPOSE: It is well known that the small GTPase RhoA modulates actin cytoskeleton and cellular contractility in the trabecular meshwork (TM). Several substances known to contract the TM reduce outflow facility, whereas cellular relaxation is commonly associated with the opposite effect. Inhibitors of the RhoA pathway are under development as antiglaucoma drugs. Here the authors investigate the role of platelet-derived growth factor (PDGF), a known activator of the Rac1 pathway, in cell cytoskeleton, outflow facility, and intraocular pressure (IOP). METHODS: Effects of PDGF on actin cytoskeleton, Rac1, and AKT activation were tested in preconfluent and confluent bovine TM cells in culture. Rac1 and AKT/P-AKT activation were assessed by Western blot analysis. Trabecular outflow facility was measured in bovine perfused anterior segments. Changes in IOP were measured for up to 6 hours after topical application in the cornea of rabbit eyes by means of a contact tonometer. RESULTS: In TM cells, PDGF (10 ng/mL) activated Rac1 through AKT and induced actin cytoskeleton rearrangement with lamellipodia formation. In this sense, lamellipodia formation in TM cells was prevented by NSC23766, a Rac1 inhibitor, and LY294002, a PI3K inhibitor. In perfused anterior segments, PDGF (100 ng/mL) increased trabecular outflow facility by 26%. In vivo, when topically applied to rabbit corneas, PDGF induced a 20% decrease in IOP (100 ng/mL). This reduction was concentration dependent and presented an EC(50) value of 2.7 nM. CONCLUSIONS: PDGF, by activating the Rac1 pathway, induces cytoskeletal changes in TM cells that enhance outflow facility. Decreased IOP after PDGF application is likely caused by the facilitation of aqueous humor outflow. Rac1 pathway activation appears to be a positive modulator of outflow facility and an interesting target for decreasing IOP after ocular hypertension.

Identification and functional characterization of ClC-2 chloride channels in trabecular meshwork cells.

In the eye, trabecular meshwork (TM) cell volume may be an important determinant of aqueous humor outflow. Among their functions, ClC-2 chloride channels are thought to be involved in regulation of cellular volume and intracellular [Cl(-)]. We characterized the properties and modulation of an inwardly rectifying chloride current activated in these cells. Patch-clamp recordings revealed inwardly rectifying chloride currents activated by membrane hyperpolarization in primary cultures of both bovine (BTM) and human (HTM) TM cells. Electrophysiological properties and anion permeability sequence (Cl(-)>Br(-)>I(-)>F(-)) were in agreement with previous data for ClC-2 in other cells. The currents were blocked by Cd(2+) and enhanced by extracellular acidification, 8Br-cAMP and cell swelling, while extracellular alkalinization decreased them. RT-PCR experiments using total RNA revealed the molecular expression of ClC-2 channels. Previously we reported the involvement of swelling-activated chloride channels (Cl(swell)) and Ca(2+)-activated K(+) channels (BK(Ca)) in cell volume and outflow facility regulation. However, in the present analysis, cell volume experiments in calcein-loaded cells and outflow facility studies performed in bovine anterior segments revealed that ClC-2 channels do not make a significant contribution to the recovery of cellular volume or to the regulation of the outflow facility. Nevertheless, ClC-2 modulation by different stimuli may contribute to intracellular [Cl(-)] regulation and other cellular functions yet to be determined in the TM.

Differential expression of the human chloride channel genes in the trabecular meshwork under stress conditions.

Among other channels, voltage-gated chloride channels (ClC) regulate cell volume, membrane potential and cellular transport. Because changes in trabecular meshwork (TM) cell volume influence outflow facility and because the relative abundance of a gene's transcript is an indication of the relevance of the gene's function, we investigated the presence and relative expression of seven members of the CLCN gene family in the human TM. To elucidate the role of ClC-2 and ClC-3 in cell swelling, we studied changes in their mRNA levels after hypotonic shock. In addition, to examine the potential involvement of these two channels in conditions associated with glaucoma, we determined their transcripts levels in response to elevated intraocular pressure (IOP) and dexamethasone (DEX). For our evaluations, we used non-transformed human TM cells and perfused human anterior segments from post-mortem donors. For hypotonic shock, cells were exposed to 260 mOsm kg(-1) medium for 15 and 30 min. For DEX, cells were treated with 0.1 microm DEX for 1, 4 and 10 days. For elevated IOP, one eye of each pair of perfused human anterior segments was subjected to DeltaP 38+/-4 mm Hg for 1 hr, 4 and 7 days while the contralateral remained at baseline pressure as a control. ClCs transcripts were determined by relative quantitative RT-PCR. Our results showed that all transcripts but ClC-1 were detected in HTM cells. ClC-2 and ClC-3 were the most abundant and comprised about twice the amount of ClC-6 and ClC-7 and four times that of ClC-4 and ClC-5. Hypotonic conditions consistently up regulated CLCN2 and slightly up regulated CLCN3. After short periods of elevated pressure, ClC-2 and ClC-3 transcripts were increased but ClC-2 induction was significantly higher than that of ClC-3. In contrast, after long pressure insults (7 days), ClC-3 mRNA was significantly increased while CLCN2 was not changed. DEX treatment markedly down regulated CLCN3 and little, if any, reduced ClC-2. The extent of response of the CLCN2 and CLCN3 to these conditions was markedly affected by individual traits but at all times maintained the relative expression pattern of both genes. CLCN2 gene expression was predominantly influenced by cell volume regulation while that of CLCN3 was preferentially affected by conditions associated with TM pathology.

Effects of dinucleoside polyphosphates on trabecular meshwork cells and aqueous humor outflow facility.

The most important risk factor for the development of glaucoma is elevated intraocular pressure (IOP). Hypotensive drugs decrease IOP, preventing optic nerve damage and further vision loss. The balance between aqueous humor (AH) production and drainage determines IOP, and problems in AH outflow pathways are associated with open-angle glaucoma development. Previous studies have shown the presence of diadenosine tetraphosphate (Ap(4)A) and pentaphosphate (Ap(5)A) in the AH. Topic application of Ap(4)A to the cornea decreased IOP, whereas Ap(5)A increased it. Because dinucleoside polyphosphates stimulate P2Y purinergic receptors, we studied their presence in trabecular meshwork (TM) cells. Additionally, the effects of diadenosine polyphosphates (Ap(n)As; n = 3-5) and Up(4)U (P(1),P(4)-(diuridine 5')-tetraphosphate; INS365) in outflow facility were tested. P2Y(1), P2Y(2), and P2Y(4) receptors were detected in TM cells by Western blot and immunocytochemistry. In TM cells, Ap(3)A, Ap(4)A, and Ap(5)A induced discrete intracellular calcium concentration ([Ca(2+)](i)) mobilizations compared with higher and more sustained [Ca(2+)](i) mobilizations after Up(4)U application. In bovine ocular anterior segments perfused at constant pressure, 1 microM Ap(3)A or Ap(4)A increased outflow facility, whereas Up(4)U or Ap(5)A did not modify it. 2-MeSADP, a selective P2Y(1) agonist, induced outflow facility increases similar to those obtained after Ap(3)A and Ap(4)A, and these were prevented by addition of the selective P2Y(1) receptor antagonist MRS-2179 (2'-deoxy-N(6)-methyladenosine-3',5'-diphosphate). Our results demonstrate that the hypotensive effect of Ap(4)A and other dinucleotides is mediated, at least in part, by increasing trabecular outflow facility through activation of P2Y(1) receptors. The latter would seem to be an interesting target in the development of antiglaucomatous drugs to selectively increase AH outflow.