Sigma-1 receptor stimulation attenuates calcium influx through activated L-type Voltage Gated Calcium Channels in purified retinal ganglion cells

Abstract

Sigma-1 receptors (σ-1rs) exert neuroprotective effects on retinal ganglion cells (RGCs) both in vivo and in vitro. This receptor has unique properties through its actions on several voltage-gated and ligand-gated channels. The purpose of this study was to investigate the role that σ-1rs play in regulating cell calcium dynamics through activated L-type Voltage Gated Calcium Channels (L-type VGCCs) in purified RGCs. RGCs were isolated from P3-P7 Sprague-Dawley rats and purified by sequential immunopanning using a Thy1.1 antibody. Calcium imaging was used to measure changes in intracellular calcium after depolarizing the cells with potassium chloride (KCl) in the presence or absence of two σ-1r agonists [(+)-SKF10047 and (+)-Pentazocine], one σ-1r antagonist (BD1047), and one L-type VGCC antagonist (Verapamil). Finally, co-localization studies were completed to assess the proximity of σ-1r with L-type VGCCs in purified RGCs. VGCCs were activated using KCl (20 mM). Pre-treatment with a known L-type VGCC blocker demonstrated a 57% decrease of calcium ion influx through activated VGCCs. Calcium imaging results also demonstrated that σ-1r agonists, (+)-N-allylnormetazocine hydrochloride [(+)-SKF10047] and (+)-Pentazocine, inhibited calcium ion influx through activated VGCCs. Antagonist treatment using BD1047 demonstrated a potentiation of calcium ion influx through activated VGCCs and abolished all inhibitory effects of the σ-1r agonists on VGCCs, implying that these ligands were acting through the σ-1r. An L-type VGCC blocker (Verapamil) also inhibited KCl activated VGCCs and when combined with the σ-1r agonists there was not a further decline in calcium entry suggesting similar mechanisms. Lastly, co-localization studies demonstrated that σ-1rs and L-type VGCCs are co-localized in purified RGCs. Taken together, these results indicated that σ-1r agonists can inhibit KCl induced calcium ion influx through activated L-type VGCCs in purified RGCs. This is the first report of attenuation of L-type VGCC signaling through the activation of σ-1rs in purified RGCs. The ability of σ-1rs to co-localize with L-type VGCCs in purified RGCs implied that these two proteins are in close proximity to each other and that such interactions regulate L-type VGCCs.

Afobazole Activation of σ-1 Receptors Modulates Neuronal Responses to Amyloid-β25–35

“…Incubation in the s-1-receptor antagonist BD-1047 reduced the effects of afobazole by ∼40%. The concentration and degree of block reported here is consistent with previous studies showing BD-1047 inhibition of s-1-receptor-mediated effects in cortical neurons and retinal ganglion cells (Katnik et al, 2006, Cuevas et al, 2011a, Mueller et al, 2013. The lack of involvement of s-2 receptors is confirmed by results obtained using the s-2 receptor antagonist rimcazole .…”

ER stress and ER stress-mediated apoptosis are involved in manganese-induced neurotoxicity in the rat striatum in vivo

“…5). In 347 addition, sigma-1R, another ER chaperone protein, exerts neuro-348 protective effects on nerve cells (Mueller et al, 2013). Our results 349 also suggested that the expression of sigma-1R was significant 350 increased (Fig.…”

Sigma Receptor Ligand, (+)-Pentazocine, Suppresses Inflammatory Responses of Retinal Microglia

“…22,23,25,26,42 Within the DR model, RGCs, in particular, were protected. 27 In addition, Ha et al 17 have observed that rR1 knockout mice display a late-onset inner retinal dysfunction with some similarities to glaucoma.…”

“…Cell types throughout the retina that contain rR1 include ganglion cells, inner nuclear layer cells, photoreceptors, and retinal pigment epithelium. 17,18 Within the nervous system, rR1 has been shown to regulate several processes including N-methyl-D-aspartate receptor and K þ channel activity, 19 neuritogenesis, 20,21 L-type voltage-gated calcium channel activity, 22,23 and microglial activity. 24 However, the complete endogenous function of this protein is not known.…”