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The Journal of Neuroscience, November 7, 2007, 27(45):12168-12175; doi:10.1523/JNEUROSCI.3541-07.2007

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Cellular/Molecular
Somatostatin Peptides Produce Multiple Effects on Gating Properties of Native Cone Photoreceptor cGMP-Gated Channels That Depend on Circadian Phase and Previous Illumination

Shih-Kuo Chen, Gladys Y.-P. Ko, and Stuart E. Dryer

Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001

Correspondence should be addressed to Dr. Stuart E. Dryer, Department of Biology and Biochemistry, University of Houston, 4800 Calhoun Road, Houston, TX 77204-5001. Email: SDryer{at}uh.edu

A subpopulation of avian amacrine cells expresses somatostatin-14 (SS14) and somatostatin-28 (SS28), which provide a potential efferent limb for light-dependent regulation of photoreceptors. Here, we demonstrate that SS14 and SS28 modulate cone photoreceptor cGMP-gated channels (CNGCs) through multiple mechanisms. In chicken cones cultured in constant darkness for 2 d after previous entrainment to light–dark (LD) cycles or in cells maintained in LD, application of 100 nM SS14 or 100 nM SS28 for either 15 min or 2 h caused a decrease in the sensitivity of CNGCs to cGMP during the night, at circadian time 16 (CT16)–CT20 or zeitgeber time 16 (ZT16)–ZT20. SS14 had no effect during the day (CT4–CT8 or ZT4–ZT8). These effects persist in cells pretreated with pertussis toxin (PTX) and, like dopamine, may work to reinforce long-term circadian fluctuations in CNGCs driven by oscillators within the photoreceptors themselves. In contrast, a 15 min exposure to SS28 caused a seemingly paradoxical increase in the sensitivity of CNGCs to cGMP during the early day (ZT4–ZT6), but only in cones maintained in LD. This effect of SS28 desensitizes rapidly, is blocked by pretreatment with PTX, and is selectively mimicked by the cyclohexapeptide agonist MK-678. This transient response also requires activation of phospholipase C and protein kinase C. The transient response to SS28 may play a role in photoreceptor adaptation to rapid changes in ambient illumination. These data also show that photoreceptor responses to at least some peptide neurotransmitters depend on the previous history of light exposure.

Key words: somatostatin; dark current; circadian; phospholipase C; protein kinase C; cone; photoreceptor

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Received April 12, 2007; revised Sept. 17, 2007; accepted Sept. 17, 2007.

Correspondence should be addressed to Dr. Stuart E. Dryer, Department of Biology and Biochemistry, University of Houston, 4800 Calhoun Road, Houston, TX 77204-5001. Email: SDryer{at}uh.edu

This article has been cited by other articles:

				K. Jian, R. Barhoumi, M. L. Ko, and G. Y.-P. Ko Inhibitory Effect of Somatostatin-14 on L-Type Voltage-Gated Calcium Channels in Cultured Cone Photoreceptors Requires Intracellular Calcium J Neurophysiol, September 1, 2009; 102(3): 1801 - 1810. [Abstract] [Full Text] [PDF]

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