Sigma-1 Receptor Activation Prevents Intracellular Calcium Dysregulation in Cortical Neurons during in Vitro Ischemia

Abstract

Sigma receptors are putative targets for neuroprotection following ischemia; however, little is known on their mechanism of action. One of the key components in the demise of neurons following ischemic injury is the disruption of intracellular calcium homeostasis. Fluorometric calcium imaging was used to examine the effects of sigma receptor activation on changes in intracellular calcium concentrations ([Ca 2ϩ ] i ) evoked by in vitro ischemia in cultured cortical neurons from embryonic rats. The sigma receptor agonist, 1,3-di-o-tolyl-guanidine (DTG), was shown to depress [Ca 2ϩ ] i elevations observed in response to ischemia induced by sodium azide and glucose deprivation. Two sigma receptor antagonists, metaphitwere shown to blunt the ability of DTG to inhibit ischemiaevoked increases in [Ca 2ϩ ] i , revealing that the effects are mediated by activation of sigma receptors and not via the actions of DTG on nonspecific targets such as N-methyl-D-aspartate receptors. DTG inhibition of ischemia-induced increases in [Ca 2ϩ ] i was mimicked by the -1 receptor-selective agonists, carbetapentane, (ϩ)-pentazocine and PRE-084 [2-(4-morpholinethyl) 1-phenylcyclohexanecarboxylate hydrochloride], but not by the sigma-2-selective agonist, ibogaine, showing that activation of sigma-1 receptors is responsible for the effects. In contrast, DTG, carbetapentane, and ibogaine blocked spontaneous, synchronous calcium transients observed in our preparation at concentrations consistent with sigma receptormediated effects, indicating that both sigma-1 and sigma-2 receptors regulate events that affect [Ca 2ϩ ] i in cortical neurons. Our studies show that activation of sigma receptors can ameliorate [Ca 2ϩ ] i dysregulation associated with ischemia in cortical neurons and, thus, identify one of the mechanisms by which these receptors may exert their neuroprotective properties.Sigma receptors are widely distributed in the mammalian brain, and these receptors recognize a diverse array of centrally acting substances including opiates, antipsychotics, antidepressants, phencyclidine (PCP)-related compounds, and neurosteroids Bowen, 2000). Thus far, two sigma receptor subtypes have been identified on the basis of their pharmacological profile, with the sigma-1 receptor showing high affinity for the positive isomer of bezomorphas such as (ϩ)-pentazocine and (ϩ)-SKF-10,047, and the sigma-2 receptor having high affinity for ibogaine (Vilner and Bowen, 2000), but only the sigma-1 receptor has been cloned (Hanner et al., 1996). Sigma receptors have been implicated in numerous physiological and pathophysiological processes such as learning and memory (Senda et al., 1996), movement disorders , and drug addiction (McCracken et al., 1999). These receptors are emerging as therapeutic targets for various diseases such neuropsychiatric disorders and cancer (Casellas et al., 2004;Hayashi and Su, 2004). Moreover, the observation that several sigma receptor ligands are neuroprotective in both in vivo and in vitro models of ischemia has ...

Sigma-1R Agonist Improves Motor Function and Motoneuron Survival in ALS Mice

“…In vitro studies revealed potent neuroprotective effects of sigma-1R agonists after excitotoxic damage [18], hypoxia-mediated neurotoxicity [41], oxidative stress-induced cell death [17], or glucose deprivation [42]. In vivo studies demonstrated that sigma-1R agonists exert therapeutic actions in rats after stroke [19,20], after selective cholinergic lesions [43], and after spinal root avulsion [10].…”

σ-1 Receptor Modulation of Acid-Sensing Ion Channel a (ASIC1a) and ASIC1a-Induced Ca2+ Influx in Rat Cortical Neurons

“…Primary cortical neurons from embryonic (E18) rats were cultured as previously described by our laboratory (Katnik et al, 2006). All procedures were done in accordance with the regulations of the University of South Florida Institutional Animal Care and Use Committee.…”

“…All of these voltagegated ion channels and NMDA receptors have been shown to contribute to the demise of neurons during an ischemic insult. Our laboratory has recently shown that -1 receptors inhibit Ca 2ϩ dysregulation evoked by ischemia and that activation of receptors is neuroprotective at delayed time points in a rat model of ischemic stroke (Ajmo et al, 2006;Katnik et al, 2006). Interstitial pH in the brain remains low several hours after an ischemic event (Nedergaard et al, 1991), and pharmacological blockade of ASIC1a by amiloride or psalmotoxin1 administered even 5 h after middle cerebral artery occlusion has been shown to diminish stroke injury (Simon, 2006).…”

Neuroprotection in Glaucoma

“…There are several factors that contribute to neuroprotective ability of sigma receptors. Sigma-1 receptor's ability to bind and associate with L-type voltage gated calcium channels, regulate neuronal intracellular calcium concentrations when exposed to ischemic conditions, prevent glutamate excitotoxicity of RGCs when exposed to sigma-1 agonist (+)-pentazocine are some of the key mechanisms underlying sigma-1's neuroprotective effects Katnik at al., 2006;Dun et al, 2007). Other pathways affected by sigma-1 receptor include attenuation of intrinsic death signal of glutamate-exposed retinal cell lines, which is a likely candidate to maintain the viability, and homeostatic intracellular calcium regulation of RGCs when they are exposed to a number of noxious stimuli that cause RGC apoptosis .…”