title: Stimulation of cannabinoid (CB1) and prostanoid (EP2) receptors opens BKCa channels and relaxes ocular trabecular meshwork.
abstract: Prostanoids and cannabinoids have ocular hypotensive and neuroprotective properties. The effect of the prostanoid AH13205 (EP2), the thromboxane-mimetic U46619, the cannabinoid (CB) agonists WIN55212-2 and CP 55,940, endothelin-1 (ET-1) and 8-bromo-cAMP on the membrane currents of trabecular meshwork (TM) cells were measured using the patch-clamp technique and compared to their effects on TM contractility. Previous studies show relaxation of TM to AH 13205 and other substances that elevate cAMP, while U46619 and endothelin-1 contract TM. This study shows that after contraction (100%) with carbachol (10(-6)m), the CB agonist CP 55,940 dose-dependently reduced contractility to 83+/-4% (n=9) (10(-6)m) and 61+/-10%, (n=7) (10(-5)m). In the presence of both the CB1 antagonist AM251 (10(-6)m) and CP 55,940 (10(-5)m), the contractile response to carbachol reached 84+/-3% (n=6) of the original level. In patch-clamp experiments, membrane permeable 8-bromo-cAMP (10(-4)m) had no effect on currents of TM cells. In contrast, AH 13205 and two cannabinoids reversibly enhanced outward current through high-conductance Ca(2+)-activated K(+) channels (BKCa, BK, maxi-K) to the following values (in % of the initial value at 100 mV): AH 13205 (10(-5)m): 200+/-28% (n=6), CP 55,940 (10(-6)m): 196+/-33% (n=7), CP 55,940 (10(-5)m): 484+/-113% (n=7), WIN55212-2 (10(-5)m): 205+/-41% (n=10). Iberiotoxin (10(-7)m) completely blocked these responses. The current response to CP 55,940 (10(-5)m) could be partially blocked by the CB1 antagonist AM251 (10(-6)m). Conversely, the contractile agents in this study either caused a transient reduction in outward current (ET-1(5x10(-8)m)) or had no effect (U46619 (10(-6)m)). We conclude that stimulation of EP2 and CB1 receptors in TM is coupled to the activation of BKCa channels via a non-diffusible second messenger cascade. This effect may contribute to the relaxant activity of EP2 and CB1 agonists in isolated TM strips, modulating ocular outflow.
authors.affiliation: Department of Veterinary Physiology, Free University of Berlin, Germany. stumpff@zedat.fu-berlin.de
authors.forename: Friederike
authors.initials: F
authors.lastname: Stumpff
authors.forename: Marianne
authors.initials: M
authors.lastname: Boxberger
authors.forename: Achim
authors.initials: A
authors.lastname: Krauss
authors.forename: Rita
authors.initials: R
authors.lastname: Rosenthal
authors.forename: Susann
authors.initials: S
authors.lastname: Meissner
authors.forename: Lars
authors.initials: L
authors.lastname: Choritz
authors.forename: Michael
authors.initials: M
authors.lastname: Wiederholt
authors.forename: Hagen
authors.initials: H
authors.lastname: Thieme
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000328:Adult; D000368:Aged; D000818:Animals; D048588:Benzoxazines; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002186:Cannabinoids / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D003511:Cyclohexanols / Q000494:pharmacology; D019332:Endothelin-1 / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects*; D008875:Middle Aged; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011466:Prostanoic Acids / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors / Q000187:drug effects*; D018078:Receptors, Prostaglandin E / Q000037:antagonists & inhibitors / Q000187:drug effects*; D013268:Stimulation, Chemical; D014129:Trabecular Meshwork / Q000187:drug effects* / Q000502:physiology
chemical_list: D048588:Benzoxazines; D002121:Calcium Channel Blockers; D002186:Cannabinoids; D018679:Cholinergic Agonists; D003511:Cyclohexanols; D019332:Endothelin-1; D009025:Morpholines; D009281:Naphthalenes; D010455:Peptides; D010880:Piperidines; D024681:Potassium Channels, Calcium-Activated; D011466:Prostanoic Acids; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D018078:Receptors, Prostaglandin E; C081039:AH 13205; D015124:8-Bromo Cyclic Adenosine Monophosphate; C103505:AM 251; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C064719:iberiotoxin; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D002217:Carbachol; D000242:Cyclic AMP; D002118:Calcium