We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Retrograde endocannabinoid inhibition of goldfish retinal cones is mediated by 2-arachidonoyl glycerol.
- Authors
SHIH-FANG FAN; STEPHEN YAZULLA
- Abstract
A functional role for retinal endocannabinoids has not been determined. We characterized retrograde suppression of membrane currents of goldfish cones in a retinal slice. Whole-cell recordings were obtained from cone inner segments under voltage clamp. IK(V)was elicited by a depolarizing pulse to +54 mV from a holding potential of −70 mV. A fifty-millisecond puff of saline with 70 mM KCl or Group I mGluR agonist DHPG was applied through a pipette directly at a mixed rodcone (Mb) bipolar cell body. The amplitude of IK(V)decreased 25% compared to the pre-puff control. Retrograde suppression of IK(V)was blocked by CB1 receptor antagonist, SR141716A. The FAAH inhibitor URB597 had no effect on the suppression of IK(V), whereas nimesulide, a COX-2 inhibitor, prolonged the effects of the K+puff 10-fold. Orlistat, a blocker of 2-AG synthesis, blocked the effect of the K+puff. Group I mGluR activation of Gq11 was demonstrated in that a puff with DHPG decreased IK(V)of cones by 32%, an effect blocked by SR141716A. The effect of DHPG was not blocked by the mGluR5 antagonist MPEP, indicating involvement of mGluR1. The suppressive effect of the K+puff vanished in a Ca2+-free, 2 mM Co2+saline. TMB-8 or ryanodine, blocked the effect of DHPG, but not that of the K+puff, showing that calcium influx or release from intracellular stores could mediate retrograde release. We suggest that retrograde suppression of cone IK(V)is mediated by Ca2+-dependent release of 2-AG from Mb bipolar cell dendrites by separate mechanisms: (1) voltage-dependent, mimicked by the K+puff, that may be activated by the depolarizing ON response to light; (2) voltage-independent, occurring under ambient illumination, mediated by tonic mGluR1 activation. The negative feedback of this latter mechanism could regulate tonic glutamate release from cones within narrow limits, regardless of ambient illumination.
- Subjects
CANNABINOIDS; GOLDFISH; PULSE (Heart beat); CALCIUM antagonists; SALINE solutions
- Publication
Visual Neuroscience, 2007, Vol 24, Issue 3, p257
- ISSN
0952-5238
- Publication type
Article
- DOI
10.1017/S095252380707006X