cGMP/cGMP-dependent protein kinase pathway modulates nicotine-induced currents through the activation of α-bungarotoxin-insensitive nicotinic acetylcholine receptors from insect neurosecretory cells.

Insect neurosecretory cells, called dorsal unpaired median neurons, are known to express two α-bungarotoxin-insensitive nicotinic acetylcholine receptor (nAChR) subtypes, nAChR1 and nAChR2. It was demonstrated that nAChR1 was sensitive to cAMP/cAMP-dependent protein kinase (PKA) regulation, resulting in a modulation of nicotine currents. In this study, we show that cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG) pathway modulates nicotine-induced currents, as increased cGMP affects the second compound of the biphasic current-voltage curve, corresponding to the nAChR2 receptors. Indeed, maintaining the guanosine triphosphate level with 100 µM guanosine triphosphate-γ-S increased nicotine currents through nAChR2. We also demonstrated that inhibition of PKG activity with 0.2 µM (8R,9S,11S)-(-)-9-methoxy-carbamyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cycloocta-(c,d,e)-trinden-1-one (KT5823), a PKG specific inhibitor, reduced nicotine-induced current amplitudes. KT5823 effect on nicotine currents is associated with calcium (Ca(2+) ) activity because inhibition of Ca(2+) concentration with cadmium chloride (CdCl2 ) abolished KT5823-induced inhibition mediated by nAChR2. However, specific inhibition of nitric oxide-guanylyl cyclase (GC) complex by 10 µM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) significantly increased nicotine-induced current amplitudes on both nAChR1 and nAChR2. These results suggest that nicotine-induced currents mediated by both α-bungarotoxin-insensitive nAChR1 and nAChR2 are coupled to the cGMP/PKG pathway. We propose that nicotinic acetylcholine receptor activation induces an increase in intracellular calcium (Ca(2+) ) concentration. Elevation of intracellular Ca(2+) results in the formation of Ca(2+) -calmodulin (CaM) complex, which activates guanylyl cyclase (GC) and/or adenylyl cyclase (AC). Ca(2+) -CaM complex could activate Ca(2+) calmodulin kinase II which could directly or indirectly modulate the nicotinic response. The mechanisms by which cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) interact remain unclear. We demonstrate that nicotine-induced currents are coupled to the cGMP/PKG pathway.

Protective effects of phycocyanin on ischemia/reperfusion liver injuries.

In this study, phycocyanin (Pc) extracted from Spirulina platensis was used to evaluate its antioxidants effects after ischemia/reperfusion injury (IRI) using the ex-vivo model of isolated perfused rat liver. The rats were divided into eight groups : Control group, where livers were directly perfused after their removal; Cold Ischemia group (CI), livers were treated in the same way as the control group, except that after their collection, they were stored for 12 h and 24 h in the Krebs Henseleit (KH) preservation solution at 4 °C and Treated group (PHY), livers were preserved in the same way as the preceding group except that the KH solution was enriched with phycocyanin at two different concentrations. Pc, a powerful antioxidant, significantly reduced ischemia/reperfusion injury in the liver. In fact, the addition of phycocyanin to the preservation solution significantly decreased the activity of liver transaminases (AST) and (ALT), alkaline phosphatase (ALP), the rate of lipid peroxidation (MDA) and the activity of certain antioxidant enzymes, essentially glutathione-S-transferase (GST) and glutathione peroxidase (GPx). On the other hand, Pc increases the level of thiol groups in hepatic tissues. In conclusion, the results show the Pc-enriched KH conservation solution is effective in preserving the hepatic graft and protecting it against IRI by acting as a potent antioxidant against the products of oxidative stress.

Permethrin enhances the agonist activity of dinotefuran on insect cholinergic synaptic transmission and isolated neurons.

Insect resistance mechanisms against pesticides lead to the development and the search of new pesticide combinations in order to delay the resistance. The combination of neonicotinoids with pyrethroids was currently proposed but the mode of action of these compounds at synaptic and extrasynaptic levels needs to be further explored. In the present study, we evaluated the effect of the combination of two insecticides, permethrin and dinotefuran, on cockroach cholinergic synaptic transmission and on isolated cell bodies. We first found that combination of 5 µM permethrin and dinotefuran enhances depolarization of the sixth abdominal ganglion compared to dinotefuran alone, without an inhibition of the spontaneous activity. However, a pretreatment with 1 µM dinotefuran or permethrin before bath application of the mixture inhibits the ganglionic depolarization. Compared to permethrin, 1 µM dinotefuran induces a persistent enhancement of spontaneous activity. Interestingly, at extrasynaptic level, using dorsal unpaired median neurons and Kenyon cells, we found that combination of both 1 µM dinotefuran and permethrin resulted in an increase of the mixture-induced current amplitudes. Pretreatment with 1 µM dinotefuran strongly decreases the currents whereas permethrin induces a time-dependent inhibition. These data demonstrate that the combination of dinotefuran and permethrin enhances the effect of dinotefuran.