Somatostatin coupling to adenylyl cyclase activity in the mouse retina

Abstract

The peptide somatostatin-14 (SRIF) acts in the mammalian retina through its distinct receptors (sst(1-5)). Scarce information is available on SRIF function in the retina, including the elucidation of transduction pathways mediating SRIF action. We have investigated SRIF and SRIF receptor modulation of adenylyl cyclase (AC) activity in both wild-type (WT) retinas and sst1 or sst2 knock-out (KO) retinas, which are known to over-express sst2 or sst1 receptors respectively. In WT retinas, application of SRIF compounds does not affect forskolin-stimulated AC activity. In contrast, activation of sst1 or sst2 receptors inhibits AC in the presence of sst2 or sst1 receptor antagonists respectively. Results from sst1 KO retinas demonstrate that either SRIF or the sst2 receptor preferring agonist octreotide, pertussis toxin-dependently inhibit AC activity. In contrast, in sst2 KO retinas, neither SRIF nor CH-275, an sst1 receptor agonist, are found to influence AC activity. As revealed by immunoblotting experiments, in sst1 KO retinas, levels of G(o)alpha proteins are 60% higher than in WT retinas and this increase in G(o)alpha protein levels is concomitant with an increase in sst2A receptor expression. We conclude that interactions between sst1 and sst2 receptors may prevent SRIF effects on AC activity. In addition, we suggest that the density of sst2 receptors and/or G(o)alpha proteins may represent the rate-limiting factor for the sst2 receptor-mediated inhibition of AC.

Expression, pharmacology, and functional role of somatostatin receptor subtypes 1 and 2 in human macrophages

“…Among synthetic ligands, we used the peptidyl multiligand analog SOM230, which binds with high affinity to sst 1,2,3,5 [42][43][44], and the peptidyl multiligand analog KE108, which binds with high affinity to all five SRIF receptors [44,45]. The sst 1 -selective peptidyl agonist CH-275 [35,41,46,47], the sst 2 -preferring peptiydyl agonist SMS 201-995 (also known as sandostatin or octreotide) [38,41,46,48,49], and the sst 2 -selective nonpeptidyl agonist L-779,976 [46, 49 -51] were also used in the absence or presence of the sst 1 -selective nonpeptydil antagonist SRA-880 [46,52,53] and the sst 2 -selective peptydil antagonist CYN [36,38,48,49,54]. All compounds were applied at 1 M, which from previous studies, is a concentration giving maximal re- ceptor occupancy [2,41].…”

The Neuropeptide Systems and their Potential Role in the Treatment of Mammalian Retinal Ischemia: A Developing Story

“…The experimental model that has been used to clarify for the first time the involvement of the sst2 receptor in the SRIF action against retinal ischemia [40] is a retina characterized by over-expression of functional sst2 receptors, caused by the genetic deletion of the sst1 receptor [28, 43-45]. It was expected that sst2 receptor agonist administration to these retinas resulted in increased protection from ischemic damage.…”

Physiology and pathology of somatostatin in the mammalian retina: A current view

“…Where the specific receptor subtype involved has been studied, it has been found that sst 2 inhibits adenylyl cyclase activity in the mouse, probably through G oα -proteins (Pavan et al, 2004). sst 2 coupling to G oα -proteins has been also demonstrated in the rabbit retina (Vasilaki et al, 2003).…”

“…Interestingly, in the mouse retina, sst 1 inhibits adenylyl cyclase activity only after elimination of the sst 2 response, suggesting that there may be interactions between sst 1 and sst 2 when they signal via adenylyl cyclase (Pavan et al, 2004). In addition, although NADPH diaphorase staining does not colocalise with sst 1 , sst 2 or sst 4 in the mouse retina (Mastrodimou et al, 2006b), the colocalisation of sst 2 with NADPH diaphorase in rod bipolar cells and photoreceptor cells of both rat and rabbit retinas has been reported (Vasilaki et al, 2001), suggesting a role of SRIF in the regulation of nitric oxide.…”