https://scholar.dgist.ac.kr/handle/20.500.11750/731 2026-04-04T15:43:03Z 2026-04-04T15:43:03Z Rhyu, Mee-Ra Kim, Yiseul Suh, Byung-Chang Jeong, Da-Jeong Bigiani, Albertino Lyall, Vijay https://scholar.dgist.ac.kr/handle/20.500.11750/60082 2026-02-11T12:10:15Z 2025-09-15T15:00:00Z

Title: Involvement of multiple taste receptors in the actions of Kokumi taste stimuli Author(s): Rhyu, Mee-Ra; Kim, Yiseul; Suh, Byung-Chang; Jeong, Da-Jeong; Bigiani, Albertino; Lyall, Vijay Abstract: Kokumi taste stimuli are ligands that activate the calcium-sensing receptor (CaSR). Kokumi stimuli elicit flavor persistence and richness, and also modulate basic tastes, such as enhance salt taste. Most γ-glutamyl peptides produce Kokumi taste as natural allosteric modulators of CaSR. We investigated the effects of γ-Glu-Cys-Gly (GSH) and γ-Glu-Val-Gly (γ-EVG) on salt taste using patch clamp technique and calcium signaling. Salt detection is mediated by at least two pathways. A Na+ selective pathway that utilizes the amiloride (Am)-sensitive epithelial Na+ channel (ENaC), and a cation non-selective pathway that is Am-insensitive. Patch-clamp studies using rat fungiform taste cells expressing ENaC provided direct evidence that GSH and γ-EVG do not alter ENaC activity. We further investigated if Kokumi taste substances can modulate salt response via the Am-insensitive pathway(s). We monitored temporal changes in [Ca2+] in HEK293T cells expressing the human vanilloid receptor 1 (hTRPV1), a non-selective cation channel, which has been suggested as a potential Am-insensitive salt taste mediator. GSH and γ-EVG induced concentration-dependent changes in [Ca2+] that were markedly attenuated in the presence of capsazepine, a specific TRPV1 antagonist. In cells expressing capsaicin-insensitive hTRPV1 mutants, the apparent affinity of hTRPV1 for GSH and γ-EVG was significantly reduced. These results suggest that multiple taste receptors may be potentially involved in the actions of Kokumi taste stimuli.

2025-09-15T15:00:00Z Yeon, Jun Hee Suh, Byung-Chang https://scholar.dgist.ac.kr/handle/20.500.11750/59014 2025-09-01T11:40:10Z 2017-02-12T15:00:00Z

Title: Stable Interaction between Voltage-Activated Ca2+ Channel α1 and β Subunits Revealed by Translocatable β Systems Author(s): Yeon, Jun Hee; Suh, Byung-Chang Abstract: High-voltage-gated Ca2+ (CaV) channels consist of a pore-forming α1 subunit and two auxiliary α2δ and β subunits. Although it is well established that CaV β promotes cell surface expression and regulates the gating properties of CaV channels, the stability of the α1-β interaction in vivo remains unclear. Here, we address this issue by engineering translocatable CaV β systems that allow the real-time measurement of the coupling in live imaging and patch-clamp. In cells without CaV α1B expression, all constructed β subunits except palmitoylated β2a were translocated to the intracellular target membranes by rapamycin application. However, in cells co-expressed with CaV α1B no translocation of the β subunits was measured up to 2 hrs. In addition, rapamycin-induced recruitment of CaV β subunits to the plasma membrane did not affected the gating properties of CaV channels. In contrast, double mutation of CaV β subunits was shown to be dissociated easily from CaV α1 by rapamycin application. In these mutant forms, dissociation of β subunit from CaV α1B lead to the decrease in current amplitude, PIP2 sensitivity and current recovery from Gβγ inhibition. Furthermore, it inhibited inactivation and shifted the voltage dependent IV curve to the right in the live cells. When cells were cotransfected with double mutated CaV β1b and β2a together, rapamycin lead to dissociation of β1b, but not β2a, from CaV α1B. The CaV α1B separated from β1b did not further interact with CaV β2a, suggesting that once dissociated, CaV α1 do not interact with other β. Taken together, our data demonstrate that the interaction of CaV α1 with β subunit is very stable in live cells.

2017-02-12T15:00:00Z Kim, Kwon Woo Suh, Byung-Chang https://scholar.dgist.ac.kr/handle/20.500.11750/59004 2025-09-01T10:40:10Z 2018-02-01T15:00:00Z

Title: Ethanol Increases Neuronal Firing by Regulating PI(4,5)P2 Sensitivity of M-Type K+ Channels Author(s): Kim, Kwon Woo; Suh, Byung-Chang Abstract: Ethanol affects the physiological functions of the central nerve systems by changing signaling pathways through the plasma membrane or by altering the membrane electrical properties. It has been reported that ethanol regulates neuronal firing by changing the gating of ion channels, including GIRK, BK, CaV, NaV and M-type potassium channels. It has been known that the M-type KCNQ2/3 channels require the membrane phosphoinositide phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for their activation. Although various studies on the physiological effects of ethanol has been reported, molecular mechanisms of the ethanol regulation on KCNQ2/3 channel gating and neuronal activity have not been studied well. Here, we have examined the molecular mechanisms for ethanol regulation of M-type KCNQ2/3 current and membrane excitability in SCG neurons. First, our data show that 100 mM and 400 mM concentrations of ethanol inhibits M-current in SCG neurons by ∼20% and ∼65%, respectively. Similar responses are found in tsA201 cells expressing the KCNQ2/3 channels. We also found that the ethanol inhibition is decreased when the cells are co-transfected with the PI(4,5)P2 synthesizing kinase PIPKIγ (∼8% inhibition in 400 mM ethanol-treated cells). In addition, KCNQ2 or KCNQ3 homomeric channels show different ethanol sensitivity, where KCNQ2 and KCNQ3 homomeric currents were inhibited by ∼40% and ∼10%, respectively, upon 200 mM ethanol application. Those results suggest that membrane PI(4,5)P2 plays an important regulator in the ethanol suppression of M-channels. In consistent, ethanol application increased neuronal firing in all three classes of SCG neurons sorted by their firing patterns (phasic-1, phasic-2 and tonic neuron). Taken together, our results suggest that ethanol elevates neuronal firing in the sympathetic SCG neurons by suppressing the M-channel activity via the suppression of PI(4,5)P2 sensitivity of KCNQ channel proteins.

2018-02-01T15:00:00Z Woo, Jin-Nyeong Suh, Byung-Chang https://scholar.dgist.ac.kr/handle/20.500.11750/58174 2025-07-25T03:33:25Z 2025-02-17T15:00:00Z

Title: Differential regulation of current kinetics by the β subunits in N-type calcium channel Author(s): Woo, Jin-Nyeong; Suh, Byung-Chang Abstract: The N-type voltage-gated calcium channel (CaV2.2) regulates synaptic transmission by controlling calcium influx during membrane depolarization. Auxiliary β subunits act as modulators for the gating properties of various calcium channels. However, the differential effects of β2 splice variants on CaV2.2 current kinetics remain unclear. Here, we elucidate how β2a and β2c subunits distinctly modulate CaV2.2 current kinetics. Using whole-cell voltage-clamp in a heterologous system, we analyzed current decay with a double exponential function model (y = Aexp(−x/τA) + Bexp(−x/τB) + y0). During 10-second depolarizing pulses, the current decayed much more slowly in CaV2.2 with β2a compared to CaV2.2 with β2c. Double exponential fitting uncovered β subunit-dependent patterns in amplitude components (A and B) and time constants (τA and τB). CaV2.2 with β2a showed a dominant slow component (A ≈ 0.88, τA ≈ 2 s) and a minor fast component (B ≈ 0.12, τB ≈ 70 ms). In contrast, CaV2.2 with β2c displayed a predominant fast component (A ≈ 0.85, τA ≈ 116 ms) and a minor slow component (B ≈ 0.15, τB ≈ 3 s). We hypothesize that components A and B represent voltage-dependent inactivation and deactivation, respectively, under sustained depolarization. β2a promotes rapid channel deactivation, allowing the current to reach equilibrium between activation and deactivation quickly with slow inactivation. Conversely, β2c induces rapid overall current decay primarily through accelerated inactivation, overshadowing the gradual deactivation process. Our findings demonstrate a significant functional divergence between membrane-anchored (β2a) and cytosolic (β2c) subunits within the β2 family, highlighting the critical role of β subunit localization in fine-tuning channel function. This study will provide novel insights into the molecular basis of calcium signaling in neurons.

2025-02-17T15:00:00Z