L-and T-type Ca^(2+)channels dichotomously contribute to retinal ganglion cell injury in experimental glaucoma

Retinal ganglion cell apoptotic death is the main pathological characteristic of glaucoma,which is the leading cause of irreversible blindness.Disruption of Ca^(2+)homeostasis plays an important role in glaucoma.Voltage-gated Ca^(2+)channel blockers have been shown to improve vision in patients with glaucoma.However,whether and how voltage-gated Ca^(2+)channels are involved in retinal ganglion cell apoptotic death are largely unknown.In this study,we found that total Ca^(2+)current densities in retinal ganglion cells were reduced in a rat model of chronic ocular hypertension experimental glaucoma,as determined by whole-cell patch-clamp electrophysiological recordings.Further analysis showed that L-type Ca^(2+)currents were downregulated while T-type Ca^(2+)currents were upregulated at the later stage of glaucoma.Western blot assay and immunofluorescence experiments confirmed that expression of the Ca_(V)1.2 subunit of L-type Ca^(2+)channels was reduced and expression of the Ca_(V)3.3 subunit of T-type Ca^(2+)channels was increased in retinas of the chronic ocular hypertension model.Soluble tumor necrosis factor-α,an important inflammatory factor,inhibited the L-type Ca^(2+)current of isolated retinal ganglion cells from control rats and enhanced the T-type Ca^(2+)current.These changes were blocked by the tumor necrosis factor-αinhibitor XPro1595,indicating that both types of Ca^(2+)currents may be mediated by soluble tumor necrosis factor-α.The intracellular mitogen-activated protein kinase/extracellular signal-regulated kinase pathway and nuclear factor kappa-B signaling pathway mediate the effects of tumor necrosis factor-α.TUNEL assays revealed that mibefradil,a T-type calcium channel blocker,reduced the number of apoptotic retinal ganglion cells in the rat model of chronic ocular hypertension.These results suggest that T-type Ca^(2+)channels are involved in disrupted Ca^(2+)homeostasis and apoptosis of retinal ganglion cells in glaucoma,and application of T-type Ca^(2+)channel blockers,especially a specific CaV3.3 blocker,may be a potential strategy for the treatment of glaucoma.

Expression, purification and characterization of a phyA^m-phyCs fusion phytase

The phyA^m gene encoding acid phytase and optimized neutral phytase phyCs gene were inserted into expression vector pPIC9K in correct orientation and transformed into Pichiapastoris in order to expand the pH profile ofphytase and decrease the cost of production. The fusion phytase phyA^m-phyCs gene was successfully overexpressed in P. pastoris as an active and extracellular phytase. The yield of total extracellular fusion phytase activity is （25.4±0.53） U/ml at the flask scale and （159.1±2.92） U/ml for high cell-density fermentation, respectively. Purified fusion phytase exhibits an optimal temperature at 55 ℃ and an optimal pH at 5.5-6.0 and its relative activity remains at a relatively high level of above 70% in the range ofpH 2.0 to 7.0. About 51% to 63% of its original activity remains after incubation at 75 ℃ to 95 ℃ for 10 min. Due to heavy glycosylation, the expressed fusion phytase shows a broad and diffuse band in SDS-PAGE （sodium dodecyl sulfate-polyacrylamide gel electrophoresis）. After deglycosylation by endoglycosidase H （EndoHf）, the enzyme has an apparent molecular size of 95 kDa. The characterization of the fusion phytase was compared with those ofphyCs andphyA^m.

Dopamine D2 Receptor-Mediated Modulation of Rat Retinal Ganglion Cell Excitability

Ganglion cells(RGCs) are the sole output neurons of the retinal circuity. Here, we investigated whether and how dopamine D2 receptors modulate the excitability of dissociated rat RGCs. Application of the selective D2 receptor agonist quinpirole inhibited outward K^+ currents, which were mainly mediated by glybenclamide-and 4-aminopyridine-sensitive channels, but not the tetraethylammonium-sensitive channel. In addition,quinpirole selectively enhanced Nav1.6 voltage-gated Na^+ currents. The intracellular c AMP/protein kinase A,Ca^2+/calmodulin-dependent protein kinase Ⅱ, and mitogen-activated protein kinase/extracellular signal-regulated kinase signaling pathways were responsible for the effects of quinpirole on K^+ and Na^+ currents, while phospholipase C/protein kinase C signaling was not involved. Under current-clamp conditions, the number of action potentials evoked by positive current injection was increased by quinpirole. Our results suggest that D2 receptor activation increases RGC excitability by suppressing outward K+currents and enhancing Nav1.6 currents, which may affect retinal visual information processing.