Tao Jin
Email Address
phstaoj@nus.edu.sg
Organizational Units
PHYSIOLOGY
dept
YONG LOO LIN SCH OF MEDICINE
faculty
6 results
Publication Search Results
Now showing 1 - 6 of 6
Publication Urocortin II inhibits the apoptosis of mesenteric arterial smooth muscle cells via L-type calcium channels in spontaneously hypertensive rats(2006) Tao, J.; Zhang, Y.; Li, S.; Tuck, W.S.; PHYSIOLOGYPublication Activation of corticotropin-releasing factor 2 receptor inhibits Purkinje neuron P-type calcium currents via Goα-dependent PKC epsilon pathway(2009-09) Tao, J.; Zhang, Y.; Huang, H.; Jiang, X.; PHYSIOLOGYCorticotropin-releasing factor (CRF) receptors have been demonstrated to be widely expressed in the central nervous system and in many peripheral tissues of mammalians. However, it is still unknown whether CRF receptors will function in cerebellar Purkinje neurons. In the present study, we investigated the expression profile of CRF receptors in rat cerebellum and identified a novel functional role of CRFR2 in modulating Purkinje neuron P-type Ca2+ currents (P-currents). We found that CRFR2α mRNA, but not CRFR1 and CRFR2β, was endogenously expressed in rat cerebellum. Activation of CRFR2 by UCN2 inhibited P-currents in a concentration-dependent manner (IC50 ~ 0.07 μM). This inhibitory effect was abolished by astressin2B, a CRFR2 antagonist, and was blocked by GDP-β-S, pertussis toxin, or a selective antibody raised against the Goα. Inhibition of phospholipase C (PLC) blocked the inhibitory action of UCN2. The application of diacylglycerol (DAG) antagonist, 1-hexadecyl-2-acetyl-sn-glycerol, as well as inhibition of either protein kinase C or its epsilon isoform (PKCε) abolished the UCN2 effect while 1-oleoyl-2-acetyl-sn-glycerol (EI-150), a membrane-permeable DAG analogue, occluded UCN2-mediated inhibition. In addition, UCN2 significantly increases spontaneous firing frequency of Purkinje neurons in cerebellar slices. In summary, activation of CRFR2 inhibits P-currents in Purkinje neurons via Goα-dependent PLC/PKCε pathway, which might contribute to its physiological functions in the cerebellum. © 2009 Elsevier Inc. All rights reserved.Publication Expression of urocortin 2 and its inhibitory effects on intracellular Ca2+via L-type voltage-gated calcium channels in rat pheochromocytoma (PC12) cells(2006-12-04) Tao, J.; Li, S.; Zhang, Y.; Soong, T.W.; PHYSIOLOGYUrocortin 2, a new member of the corticotrophin-releasing factor (CRF) neuropeptide family, was reported to be widely expressed in the central nervous system and peripheral tissues. Here, we detected urocortin 2 mRNA in PC12 cells using reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, we observed its effects on intracellular Ca2+ concentration ([Ca 2+]i) using confocal microscopy and flow cytometry and on voltage-gated calcium channel (VGCC) currents using whole-cell patch clamp. Our results showed that urocortin 2 mRNA was coexpressed with CRF, and CRF receptor (CRFR) 2β in undifferentiated PC12 cells, but not CRFR1 or CRFR2α. KCl (40 mM) or Bay K8644 (1 μM), an L-type VGCC activator, increased [Ca 2+]i. Pretreatment of the cells with urocortin 2 significantly diminished the effect of Bay K8644 or KCl. Urocortin 2 showed no influence on [Ca2+]i in tyrode's solution containing EGTA or Ca2+-free tyrode's solution. It reversibly inhibited the VGCC currents in a concentration-dependent manner, but had no apparent effects on the cells treated with nifedipine (1 μM), an L-type VGCC blocker. Urocortin 2 up-shifted the current-voltage curves. No frequency-dependence of urocortin 2 effects on IBa was observed. The inhibitory effects of urocortin 2 on VGCC currents or [Ca2+]i were not affected by astressin 2B, an antagonist of CRFR2. As calcium overload play a key role in some neuronal degenerative diseases such as Alzheimer's and Parkinson's diseases, our results suggest that urocortin 2 may be a potentially interesting agent for the treatment of these diseases. © 2006 Nature Publishing Group All rights reserved.Publication Separate locations of urocortin and its receptors in mouse testis: Function in male reproduction and the relevant mechanisms(2007) Tao, J.; Lin, M.; Sha, J.; Li, S.; GREGORY TAN MING YEONG; Soong, T.W.; PHYSIOLOGYPublication Effects of celecoxib on voltage-gated calcium channel currents in rat pheochromocytoma (PC12) cells(2007) Zhang, Y.; Ding, G.; Cheng, Y.; Sun, W.; Tao, J.; Huang, H.; PHYSIOLOGYCyclooxygenase-2 (COX-2) plays crucial roles in the development and invasion of tumors. Celecoxib, a selective COX-2 inhibitor, has been shown to be chemopreventive against cancer. However, to date, the mechanisms of these effects remain unclear. In this study, we investigate the effects of celecoxib on voltage-gated calcium channel (VGCC) currents in undifferentiated pheochromocytoma (PC12) cells using whole-cell patch clamp. Our results showed that celecoxib, instead of rofecoxib or NS-398, another selective COX-2 inhibitor, reversibly inhibited the current density of VGCC in a concentration-dependent manner, but had no apparent effects on the cells treated with nifedipine (1 μM), an L-type calcium channel blocker. Upon pre-incubation of PC12 cells with omega-conotoxia GVIA (1 μM), an N-type calcium channel blocker, omega-agatoxin IVA (1 μM), a P/Q-type calcium channel blocker, or SNX-482 (1 μM), a R-type calcium channel blocker, celecoxib (1 μM) inhibited the currents by 36%, 28%, and 25%, respectively. Celecoxib up-shifted the current-voltage (I-V), and hyperpolarizedly shifted the inactivation curve, but did not markedly affect the activation curve. Intracellular application of H89, a protein kinase A inhibitor, failed to affect the celecoxib's VGCC currents inhibition. Taken together, our present results suggested that celecoxib inhibited L-type calcium channels in PC12 cells via a COX-2 independent pathway, which might be responsible for its clinical effects including anti-tumor. © 2007.Publication Tyrosine kinase-independent inhibition by genistein on spermatogenic T-type calcium channels attenuates mouse sperm motility and acrosome reaction(2009) Tao, J.; Soong, T.W.; Zhang, Y.; Sun, W.; Li, S.; PHYSIOLOGYAlthough the protein tyrosine kinase (PTK) inhibitor, genistein, has been widely used to investigate the possible involvement of PTK during reproductive functions, it is unknown whether it modulates sperm calcium channel activity. In the present study, we recorded T-type calcium currents (ICa,T) in mouse spermatogenic cells using whole-cell patch clamp and found that extracellular application of genistein reversibly decreased ICa,T in a concentration-dependent manner (IC50 ∼22.7 μM). To determine whether TK activity is required for ICa,T inhibition, we found that peroxovanadate, a tyrosine phosphatase inhibitor, was ineffective in preventing the inhibitory effect of genistein. Furthermore, intracellular perfusion of the cells with ATP-γ-S also did not alter the inhibitory effect of genistein. To further reveal the direct inhibitory mechanism of genistein on ICa,T, we applied into the bath lavendustin A, a PTK inhibitor structurally unrelated to genistein, and found that the current amplitude remained unchanged. Moreover, daidzein, an inactive structural analog of genistein, robustly inhibited the currents. The inhibitory effect of genistein on T-type calcium channels was associated with a hyperpolarizing shift in the voltage-dependence of inactivation. Genistein was observed to decrease sperm motility and to significantly inhibit sperm acrosome reaction (AR) evoked by zona pellucida. Using transfected HEK293 cells system, only Cav3.1 and Cav3.2, instead of Cav3.3, channels were inhibited by genistein. Since T-type calcium channels are the key components in the male reproduction, such as in AR and sperm motility, our data suggest that this PTK-independent inhibition of genistein on ICa,T might be involved in its anti-reproductive effects. © 2008 Elsevier Ltd. All rights reserved.