Purchase this article with an account.
S. Yazulla, S.–F. Fan; Mechanism of Retrograde Transmission of Endocannabinoids From Bipolar Cells to Cones in Goldfish Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1508.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
We reported last year that endocannabinoids (eCBs) provided a retrograde signal from bipolar cells to cones in goldfish retina (ARVO abstract 2261, 2005). A short puff of K+–saline directed at bipolar cells modulated IK(V) of long single cones (LSC). All effects were blocked by the CB1 receptor antagonist SR 141716A, indicating involement of an eCB. Here we explored the mechanism of the retrograde eCB effects in an attempt to determine whether anandamide or 2–arachidonylglycerol (2–AG) was the likely eCB.
Experiments were performed on goldfish retinal slices. Whole–cell recordings were obtained from the inner segment of LSC under voltage clamp (holding potential –70 mV). IK(V) of LSC was elicited by a single +124 mV depolarization pulse. A single puff (50 or 200 msec, 15 psi) of physiological saline with 70 mM KCl or 0.2 mM mGluR agonist ACPD was applied through a pipette (tip diameter ∼2 µm) within a few µm of a mixed rod/cone (Mb) bipolar cell body.
1. The amplitude of IK(V), recorded ∼400 msec after the K+ puff, either decreased to 77 ± 5% (mean ± S.E., n = 10) or increased to 139 ± 15% (n = 5) relative to the pre–puff control. 2. The fatty acid amide hydrolase inhibitor (FAAH) URB597 had no effect on the changes of IK(V) in response to the K+ puff at either 100 nM (n = 4) or 100 µM (n = 5), suggesting that anandamide was not the retrograde eCB. 3. A cyclooxygenase–2 (COX–2) inhibitor (nimesulide, 30 µM) prolonged the effects of the K+ puff 10–fold (3.7±2 min to 36±14 min), suggesting that 2–AG was the retrograde eCB. 4. Diacylglycerol lipase (DGL) is a key enzyme in the synthesis of 2–AG. A blocker of DGL, orlistat (10 µM), completely suppressed the effect of the K+ puff (n = 5). 5. The effect of the K+ puff also vanished in a Ca2+–free, 2mM Co2+ saline (n = 8). 6. A puff with ACPD decreased IK(V) of LSC to 78 ± 7% (n = 10) of control, presumably mediated by release of Ca2+ from intracellular stores in response to activation of mGluR.
Retrograde modulation of IK(V) of goldfish cones is mediated by Ca2+–dependent release of 2–AG from Mb bipolar cell dendrites. COX–2, rather than FAAH likely terminates the retrograde effect. We suggest that a retrograde release of 2–AG from bipolar cell dendrites may occur in the light or dark by separate mechanisms controlling intracellular Ca2+: a voltage–independent mechanism in the dark by tonic mGluR activation and consequent release of intracellular Ca2, and, a voltage–dependent mechanism that is activated during the ON response to light.
This PDF is available to Subscribers Only