• Journal of Plant Biology
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• v.36 no.1
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• pp.59-66
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• 1993

In maize coleoptile segments where auxin transport capacity decreases with time following excision, susceptability of the tissue to transport inhibitors such as N-1-naphthylphthalamic acid (NPA), 3,4,5-triiodobenzoic acid (TIBA) or high concentrations of IAA was found to be rather increased. A time-dependent increase in the sensitivity to NPA can be postulated since the dose-response curve for NPA was shifted in the‘aged’tissue to the left (i.e. lower concentration). Preincubation of the tissue at a low temperature abolished the time-dependent sensitivity change, suggesting that cellular metabolism could be involved. The NPA-sensitive state was also brought about by calcium depletion of the tissue, which can be partially reversed by addition of calcium. Presence of exogenous IAA in the preincubation medium kept the auxin transport system from decay, implicating auxin as an endogenous controlling factor. Results of our experiments indicate a reversible, time-dependent changes of auxin transport system in which transport capacity and sensitivity to NPA are tightly coupled. Changes in the sensitivity to NPA were also seen in auxin action as well.

• Journal of Biosystems Engineering
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• v.32 no.1 s.120
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• pp.37-43
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• 2007

This study was carried out to investigate the applicability of PVC membrane-based ion-selective electrodes for macronutrients (K, Ca, and N) by measuring of potassium, calcium, nitrate ions in hydroponic nutrient solution. The capabilities of two ion-selective membranes with varying chemical compositions for each ion were evaluated in terms of sensitivity, selectivity, and lifetime to choose sensing elements suitable for measuring typical ranges of nutrient concentrations in hydroponic solutions. The selected calcium and nitrate ion-selective membranes showed effectively sensitive responses to calcium and nitrate ions with lifetimes of 25 and 15 days, respectively. The addition of a cation additive to the potassium membrane cocktail allowed its sensitivity to be increased whereas its lifetime was reduced from 30 days to 10 days.

• BMB Reports
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• v.33 no.3
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• pp.202-207
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• 2000

The depletion of intracellular calcium stores by thapsigargin treatment evoked extracellular calcium-dependent membrane currents in Xenopus laevis oocytes. These currents have been compared to those evoked by microinjection of a calcium influx factor (CIF) purified from Jurkat T lymphocytes. The membrane currents elicited by thapsigargin treatment (peak current, $163{\pm}60$ nA) or CIF injection (peak current, $897{\pm}188$ nA) were both dependent on calcium entry, based on their eradication by the removal of extracellular calcium. The currents were, in both cases, attributed primarily to well-characterized $Ca^{2+}-dependent$ $Cl^-$ currents, based on their similar reversal potentials (-24 mV vs. -28 mV) and their inhibition by niflumic acid (a $Cl^-$ channel blocker). Currents induced by either thapsigargin treatment or CIF injection exhibited an identical pattern of inhibitory sensitivity to a panel of lanthanides, suggesting that thapsigargin treatment or CIF injection evoked $Cl^-$ currents by stimulating calcium influx through pharmacologically identical calcium channels. These results indicate that CIF acts on the same calcium entry pathway activated by the depletion of calcium stores and most lanthanides are novel pharmacological tools for the study of calcium entry in Xenopus oocytes.

• BMB Reports
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• v.56 no.3
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• pp.172-177
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• 2023

BEST family is a class of Ca²⁺-activated Cl- channels evolutionary well conserved from bacteria to human. The human BEST paralogs (BEST1-BEST4) share significant amino acid sequence homology in the N-terminal region, which forms the transmembrane helicases and contains the direct calcium-binding site, Ca²⁺-clasp. But the cytosolic C-terminal region is less conserved in the paralogs. Interestingly, this domain-specific sequence conservation is also found in the BEST1 orthologs. However, the functional role of the C-terminal region in the BEST channels is still poorly understood. Thus, we aimed to understand the functional role of the C-terminal region in the human and mouse BEST1 channels by using electrophysiological recordings. We found that the calcium-dependent activation of BEST1 channels can be modulated by the C-terminal region. The C-terminal deletion hBEST1 reduced the Ca²⁺-dependent current activation and the hBEST1-mBEST1 chimera showed a significantly reduced calcium sensitivity to hBEST1 in the HEK293 cells. And the C-terminal domain could regulate cellular expression and plasma membrane targeting of BEST1 channels. Our results can provide a basis for understanding the C-terminal roles in the structure-function of BEST family proteins.

• Molecules and Cells
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• v.44 no.2
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• pp.88-100
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• 2021

Anoctamin 6/TMEM16F (ANO6) is a dual-function protein with Ca2+-activated ion channel and Ca2+-activated phospholipid scramblase activities, requiring a high intracellular Ca2+ concentration (e.g., half-maximal effective Ca2+ concentration [EC50] of [Ca2+]i > 10 μM), and strong and sustained depolarization above 0 mV. Structural comparison with Anoctamin 1/TMEM16A (ANO1), a canonical Ca2+-activated chloride channel exhibiting higher Ca2+ sensitivity (EC50 of 1 μM) than ANO6, suggested that a homologous Ca2+-transferring site in the N-terminal domain (Nt) might be responsible for the differential Ca2+ sensitivity and kinetics of activation between ANO6 and ANO1. To elucidate the role of the putative Ca2+-transferring reservoir in the Nt (Nt-CaRes), we constructed an ANO6-1-6 chimera in which Nt-CaRes was replaced with the corresponding domain of ANO1. ANO6-1-6 showed higher sensitivity to Ca2+ than ANO6. However, neither the speed of activation nor the voltage-dependence differed between ANO6 and ANO6-1-6. Molecular dynamics simulation revealed a reduced Ca2+ interaction with Nt-CaRes in ANO6 than ANO6-1-6. Moreover, mutations on potentially Ca2+-interacting acidic amino acids in ANO6 Nt-CaRes resulted in reduced Ca2+ sensitivity, implying direct interactions of Ca2+ with these residues. Based on these results, we cautiously suggest that the net charge of Nt-CaRes is responsible for the difference in Ca2+ sensitivity between ANO1 and ANO6.

• BMB Reports
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• v.51 no.5
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• pp.236-241
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• 2018

Anoctamin 1 (ANO1) is an anion channel that is activated by changes in cytosolic $Ca^{2+}$ concentration and noxious heat. Although the critical roles of ANO1 have been elucidated in various cell types, the control of its gating mechanisms by $Ca^{2+}$ and heat remain more elusive. To investigate critical amino acid residues for modulation of $Ca^{2+}$ and heat sensing, we constructed a randomized mutant library for ANO1. Among 695 random mutants, reduced $Ca^{2+}$ sensitivity was observed in two mutants (mutant 84 and 87). Consequently, the E143A mutant showed reduced sensitivity to $Ca^{2+}$ but not to high temperatures, whereas the E705V mutant exhibited reduced sensitivity to both $Ca^{2+}$ and noxious heat. These results suggest that the glutamic acids (E) at 143 and 705 residues in ANO1 are critical for modulation of $Ca^{2+}$ and/or heat responses. Furthermore, these findings help to provide a better understanding of the $Ca^{2+}$-mediated activation and heat-sensing mechanism of ANO1.

• YAKHAK HOEJI
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• v.34 no.3
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• pp.180-191
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• 1990

A comparison was made of the effects of selective ${\alpha_1}-adrenoceptor$ agonist phenylephrine and selective ${\alpha_2}-adrenoceptor$ agonist clonidine on endothelium-containing and endothelium-denuded rings of the rat aorta. In the case of phenylephrine, removal of endothelium increased sensitivity 2.5 fold at $EC_{50}$ level and maximum contractive response 1.4 fold. In the case of clonidine, which gave only 15% of maximum contractive response given to phenylephrine on endothelium-containing rings, removal of the endothelium increased sensitivity 5.6 fold at $EC_{50}$ level and maximum contractive response 5 fold, which was about 55% of that given by phenylephrine. In endothelium-denuded ring, phenylephrine-induced contraction tended to be more increased in tonic contraction than in phasic contraction as compared to that in endothelium-containing ring, while clonidine-induced contraction was monophasic and was increased only in tonic contraction. In the calcium-free solution or in the presence, of verapamil, contraction stimulated by clonidine was almost abolished while that stimulated by phenylephrine produced only phasic contraction. The depression of sensitivity to these agonists in rings with endothelium appeared to be due to the vasodepressor action of endothelium derived relaxing factor (EDRF), because hemoglobin, a specific blocking agent of EDRF, abolished this depression. It is unlikely that the endothelium-dependent relaxation was due to stimulation of release of EDRF, because clonidine did not produce endothelium-dependent relaxation in 5-hydroxytryptamine-precontracted ring even when its contractile action was blocked by the ${\alpha_1}-adrenoceptor$ antagonist, prazosin. When the efficacy of phenylephrine was reduced to about the initial efficacy of clonidine by pretreatment with dibenamine, the contraction-response curves for phenylephrine became very similar to the corresponding curves obtained for clonidine before receptor inactivation. In the dibenamine-treated rings, contraction of phenylephrine was abolished in calcium-free solution or in the presence of verapamil like that obtained for clonidine before receptor inactivation. These results suggest that EDRF spontaneously released from endothelium depress contraction more profoundly in a case of an agonist with low efficacy and the phenylephrine-induced contraction was totally dependent on extracellular calcium as was that obtained for clonidine when the efficacy of phenylephrine was reduced to that of clonidine by irreversible inactivation of ${\alpha_1}-adrenoceptor$ with dibenamine.

• The Korean Journal of Physiology and Pharmacology
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• v.11 no.5
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• pp.215-219
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• 2007

Small and large conductance $Ca^{2+}$-activated $K^+(SK_{Ca}\;and\;BK_{Ca})$ channels are implicated in the modulation of neuronal excitability. We investigated how changes in peripheral $K_{Ca}$ channel activity affect mechanical sensitivity as well as the afferent fiber type responsible for $K_{Ca}$ channel-induced mechanical sensitivity. Blockade of $SK_{Ca}$ and $BK_{Ca}$ channels induced a sustained decrease of mechanical threshold which was significantly attenuated by topical application of capsaicin onto afferent fiber and intraplantar injection of 1-ethyl-2-benzimidazolinone. NS1619 selectively attenuated the decrease of mechanical threshold induced by charybdotoxin, but not by apamin. Spontaneous flinching and paw thickness were not significantly different after $K_{Ca}$ channel blockade. These results suggest that mechanical sensitivity can be modulated by $K_{Ca}$ channels on capsaicin-sensitive afferent fibers.

• Journal of the Korean Applied Science and Technology
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• v.30 no.2
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• pp.197-203
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• 2013

The diagnostic assay of calcium ion was sought using a modified sensor with square-wave stripping voltammetry (SWSV) and cyclic voltammetry (CV). In this study, simple graphite pencil was used as working, reference, and auxiliary electrodes. By coating the working electrodes with DNA, their sensitivity was very much improved, and good results were yielded. Moreover, clean seawater was used as an electrolyte solution instead of acid and base electrolytes to lessen the expenses involved in the experiment. The analytical optimum conditions were also examined. These conditions were attained at the low detection limit of $0.6ugL^1$. After that, the results were applied to drinking water of milk contain.

• Development and Reproduction
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• v.19 no.2
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• pp.61-67
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• 2015

The immediate early gene c-fos has long been known as a molecular marker of neural activity. The neuron's activity is transformed into intracellular calcium influx through NMDA receptors and L-type voltage sensitive calcium channels. For the transcription of c-fos, neural activity should be strong enough to activate mitogen-activated protein kinase (MAPK) signaling pathway which shows low calcium sensitivity. Upon translation, the auto-inhibition by Fos protein regulates basal Fos expression. The pattern of external stimuli and the valence of the stimulus to the animal change Fos signal, thus the signal reflects learning and memory aspects. Understanding the features of multiple components regulating Fos signaling is necessary for the optimal generation and interpretation of Fos signal.