title: Meclofenamic acid blocks electrical synapses of retinal AII amacrine and on-cone bipolar cells.
abstract: Gap junction channels constitute specialized intercellular contacts that can serve as electrical synapses. In the rod pathway of the retina, electrical synapses between AII amacrine cells express connexin 36 (Cx36) and electrical synapses between AII amacrines and on-cone bipolar cells express Cx36 on the amacrine side and Cx36 or Cx45 on the bipolar side. For physiological investigations of the properties and functions of these electrical synapses, it is highly desirable to have access to potent pharmacological blockers with selective and reversible action. Here we use dual whole cell voltage-clamp recordings of pairs of AII amacrine cells and pairs of AII amacrine and on-cone bipolar cells in rat retinal slices to directly measure the junctional conductance (G(j)) between electrically coupled cells and to study the effect of the drug meclofenamic acid (MFA) on G(j). Consistent with previous tracer coupling studies, we found that MFA reversibly blocked the electrical synapse currents in a concentration-dependent manner, with complete block at 100 muM. Whereas MFA evoked a detectable decrease in G(j) within minutes of application, the time to complete block of G(j) was considerably longer, typically 20-40 min. After washout, G(j) recovered to 20-90% of the control level, but the time to maximum recovery was typically >1 h. These results suggest that MFA can be a useful drug to investigate the physiological functions of electrical synapses in the rod pathway, but that the slow kinetics of block and reversal might compromise interpretation of the results and that explicit monitoring of G(j) is desirable.
authors.affiliation: University of Bergen, Department of Biomedicine, Jonas Lies vei 91, N-5009 Bergen, Norway.
authors.forename: Margaret Lin
authors.initials: ML
authors.lastname: Veruki
authors.forename: Espen
authors.initials: E
authors.lastname: Hartveit
mesh_terms: D025042:Amacrine Cells / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001703:Biophysics; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D054351:Electrical Synapses / Q000187:drug effects*; D005136:Eye Proteins; D066298:In Vitro Techniques; D008469:Meclofenamic Acid / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D012160:Retina / Q000166:cytology*; D051245:Retinal Bipolar Cells / Q000187:drug effects / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology
chemical_list: D016861:Cyclooxygenase Inhibitors; D005136:Eye Proteins; C108488:reticalmin; D008469:Meclofenamic Acid