• Animal cells and systems
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• v.11 no.2
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• pp.169-173
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• 2007

Hyperpolarization-activated nonselective cation channels (HCNs) play a pivotal role in producing rhythmic electrical activity in the heart and the nerve cells. In our previous experiments, voltage-dependent $Cd^{2+}$ access to one of the substituted cysteines in S6, T464C, supports the existence of an intracellular voltage-dependent activation gate. Direct binding of intracellular cAMP to HCN channels also modulates gating. Here we attempted to locate the cAMP-modulated structure that can modify the gating of HCN channels. SpHCN channels, a sea urchin homologue of the HCN family, became inactivated rapidly and intracellular cAMP removed this inactivation, resulting in about eight-fold increase of steady-state current level. T464C was probed with $Cd^{2+}$ applied to the intracellular side of the channel. We found that access of $Cd^{2+}$ to T464C was strongly gated by cAMP as well as voltage. Release of bound $Cd^{2+}$ by DMPS was also gated in a cAMP-dependent manner. Our results suggest the existence of an intracellular cAMP-modulated gate in the lower S6 region of spHCN channels.

• Journal of Microbiology and Biotechnology
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• v.15 no.3
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• pp.665-671
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• 2005

Initiation and activation of sperm motility are prerequisite processes for the contact and fusion of male and female gametes at fertilization. The phenomena are under the regulation of cAMP and $Ca^{2+}$ in vertebrates and invertebrates. Mammalian sperm requires $Ca^{2+}$ and cAMP for the activation of sperm motility. Cell signaling for the initiation and activation of sperm motility in the ascidians and salmonid fishes has drawn much attention. In the ascidians, the sperm-activating and attracting factors from unfertilized egg require extracellular $Ca^{2+}$ for activating sperm motility and eliciting chemotactic behavior toward the egg. On the other hand, the cAMP-dependent phosphorylation of protein is essential for the initiation of sperm motility in salmonid fishes. A decrease of the environmental $K^+$ concentration surrounding the spawned sperm causes $K^+$ efflux and $Ca^{2+}$ influx through the specific $K^+$ channel and dihydropyridine-sensitive L-/T-type $Ca^{2+}$ channel, respectively, thereby leading to the membrane hyperpolarization. The membrane hyperpolarization induces synthesis of cAMP, which triggers further cell signaling processes, such as cAMP-dependent protein phosphorylation, to initiate sperm motility in salmonid fishes. This article reviews the studies on the physiological mechanisms of sperm motility and its cell signaling in aquatic species.

• The Korean Journal of Physiology
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• v.28 no.1
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• pp.37-50
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• 1994

Synthetic potassium channel openers (KCOs) are agents capable of opening K-channels in excitable cells. These agents are known to have their maximal potency in the smooth muscle tissue, especially in the vascular smooth muscle. Much attention has been focused on the type of K-channel that is responsible for mediating the effects of KCOs. As the KCO-induced changes are antagonized by glibenclamide, an $K_{ATP}$ (ATP-sensitive K-channel) blocker in the pancreatic ${\beta}-cell,\;K_{ATP}$ was suggested to be the channel responsible. However, there also are many results in favor of other types of K-channel $$(maxi-K,\;small\;conductance\;K_{Ca,}\; SK_{ATP}) mediating the effects of KCOs. Effects of lemakalim, (-)enantiomer of cromakalim (BRL 34915), on the spontaneous contractions and slow waves, were investigated in the antral circular muscle of the guinea-pig stomach. Membrane currents and the effects on membrane currents and single channel activities were also measured in single smooth muscle cells and excised membrane patches by using the patch clamp method. Lemakalim induced hyperpolarization and inhibited spontaneous contractions in a dose-dependent manner. These effects were blocked by glibenclamide and low concentrations of tetraethyl ammonium (< mM). Glibenclamide blocked the effect of lemakalim on the membrane potential and slow waves. The mechanoinhibitory effect of lemakalim was blocked by pretreatment with glibenclamide. In a whole ceIl patch clamp condition, lemakalim largely increased outward K currents. These outward K currents were blocked by TEA, glibenclamide and a high concentration of intracelIular EGTA (10 mM). Volatage-gated Ca currents were not affected by lemakalim. In inside-out patch clamp experiments, lemakalim increased the opening frequency of the large conductance $Ca^{2+}-activated$ K channels $(BK_{Ca},\;Maxi-K).$ From these results, it is suggested that lemakalim induces hyperpolarization by opening K-channels which are sensitive to internal Ca and such a hyperpolarization leads to the inhibition of the spontaneous contraction.

• The Korean Journal of Physiology and Pharmacology
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• v.3 no.1
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• pp.1-10
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• 1999

We sought to find out the mechanism of vascular relaxation by extracellular $K^+$ concentration $([K^+]_o)$ in the cerebral resistant arteriole from rabbit. Single cells were isolated from the cerebral resistant arteriole, and using voltage-clamp technique barium-sensitive $K^+$ currents were recorded, and their characteristics were observed. Afterwards, the changes in membrane potential and currents through the membrane caused by the change in $[K^+]_o$ was observed. In the smooth muscle cells of cerebral resistant arteriole, ion currents that are blocked by barium, 4-aminopyridine (4-AP), and tetraethylammonium (TEA) exist. Currents that were blocked by barium showed inward rectification. When the $[K^+]_o$ were 6, 20, 60, and 140 mM, the reversal potentials were $-82.7{\pm}1.0,\;-49.5{\pm}1.86,\;-26{\pm}1.14,\;-5.18{\pm}1.17$ mV, respectively, and these values were almost identical to the calculated $K^+$ equilibrium potential. The inhibition of barium-sensitive inward currents by barium depended on the membrane potential. At the membrane potentials of -140, -100, and -60 mV, $K_d$ values were 0.44, 1.19, and 4.82 ${\mu}M,$ respectively. When $[K^+]_o$ was elevatedfrom 6 mM to 15 mM, membrane potential hyperpolarized to -50 mV from -40 mV. Hyperpolarization by $K^+$ was inhibited by barium but not by ouabain. When the membrane potential was held at resting membrane potential and the $[K^+]_o$ was elevated from 6 mM to 15 mM, outward currents increased; when elevated to 25 mM, inward currents increased. Fixing the membrane potential at resting membrane potential and comparing the barium-sensitive outward currents at $[K^+]_o$ of 6 and 15 mM showed that the barium- sensitive outward current increased at 15 mM $K^+.$ From the above results the following were concluded. Barium-sensitive $K^+$?channel activity increased when $[K^+]_o$ is elevated and this leads to an increase in $K^+-outward$ current. Consequently, the membrane potential hyperpolarizes, leading to the relaxation of resistant arteries, and this is thought to contribute to an increase in the local blood flow of brain.

• The Korean Journal of Physiology and Pharmacology
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• v.8 no.1
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• pp.7-15
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• 2004

Nitric oxide (NO) system has been implicated in a wide range of physiological functions in the nervous system. However, the role of NO in regulating the neural activity in the gustatory zone of nucleus tractus solitarius (NTS) has not been established. The present study was aimed to investigate the role of NO in the gustatory NTS neurons. Sprague-Dawley rats, weighing about 50 g, were used. Whole cell patch recording and immunohistochemistry were done to determine the electrophysiological characteristics of the rostral gustatory nucleus of the tractus solitaries and distribution of NO synthases (NOS). Neuronal NOS (nNOS) immunoreactivity was strongly detected along the solitary tract extending from rostral to caudal medulla. Resting membrane potentials of NTS neurons were $-49.2{\pm}2\;mV$ and action potential amplitudes were $68.5{\pm}2\;mV$ with a mean duration measured at half amplitude of $1.7{\pm}0.3\;ms$. Input resistance, determined from the response to a 150 ms, -100 pA hyperpolarizing current pulse, was $385{\pm}15\;M{\Omega}$, Superfusion of SNAP or SNP, NO donors, produced either hyperpolarization (68%), depolarization (5%), or no effect (27%). The hyperpolarization was mostly accompanied by a decrease in input resistance. The hyperpolarization caused by SNAP or SNP increased the time to initiate the first action potential, and decreased the number of action potentials elicited by current injection. SNP or SNAP also markedly decreased the number of firing neural discharges of the spontaneous NTS neural activity under zero current. Superfusion of L-NAME, a NOS inhibitor, slightly depolarized the membrane potential and increased the firing rate of NTS neurons induced by current injection. ODQ, a soluble guanylate cyclase inhibitor, ameliorated the SNAP-induced changes in membrane potential, input resistance and firing rates. 8-Br-cGMP, a non-degradable cell-permeable cGMP, hyperpolarized the membrane potential and decreased the number of action potentials. It is suggested that NO in the gustatory NTS has an inhibitory role on the neural activity of NTS through activating soluble guanylate cyclase.

• Proceedings of the Zoological Society Korea Conference
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• 1996.10a
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• pp.172.2-172
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• 1996

No Abstract, See Full Text

• Proceedings of the Korean Biophysical Society Conference
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• 1996.07a
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• pp.35-35
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• 1996

Nitric oxide (NO) has been reported to have many roles in vivo ranging from the neurotransmitter in brain to the relaxant in smooth muscles. Recently, using inside-out patches, Bolotina et al. (1) showed that relaxing effect of NO is aortic smooth muscle is through direct activation of Ca2+-activated K+ channels (maxi-K), resulting in hyperpolarization. (omitted)

• Proceedings of the Zoological Society Korea Conference
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• 1999.10b
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• pp.175.1-175
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• 1999

No Abstract, See Full Text

• Journal of Chest Surgery
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• v.46 no.6
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• pp.402-412
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• 2013

Background: Moderate and severe hypothermia with cardiopulmonary bypass during aortic surgery can cause some complications such as endothelial cell dysfunction or coagulation disorders. This study found out the difference of vascular reactivity by phenylephrine in moderate and severe hypothermia. Methods: Preserved aortic endothelium by excised rat thoracic aorta was sectioned, and then down the temperature rapidly to $25^{\circ}C$ by 15 minutes at $38^{\circ}C$ and then the vascular tension was measured. The vascular tension was also measured in rewarming at $25^{\circ}C$ for temperatures up to $38^{\circ}C$. To investigate the mechanism of the changes in vascular tension on hypothermia, NG-nitro-L-arginine methyl esther (L-NAME) and indomethacin administered 30 minutes before the phenylephrine administration. And to find out the hypothermic effect can persist after rewarming, endothelium intact vessel and endothelium denuded vessel exposed to hypothermia. The bradykinin dose-response curve was obtained for ascertainment whether endothelium-dependent hyperpolarization factor involves decreasing the phenylnephrine vascular reactivity on hypothermia. Results: Fifteen minutes of the moderate hypothermia blocked the maximum contractile response of phenylephrine about 95%. The vasorelaxation induced by hypothermia was significantly reduced with L-NAME and indomethacin administration together. There was a significant decreasing in phenylephrine susceptibility and maximum contractility after 2 hours rewarming from moderate and severe hypothermia in the endothelium intact vessel compared with contrast group. Conclusion: The vasoplegic syndrome after cardiac surgery might be caused by hypothermia when considering the vascular reactivity to phenylephrine was decreased in the endothelium-dependent mechanism.

• Journal of Microbiology and Biotechnology
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• v.14 no.3
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• pp.456-465
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• 2004

$K^+$ efflux through a certain type of $K^+$ channels causes the change of membrane potential and leads to cAMP synthesis in the transmembrane cell signaling for the initiation of sperm motility in the salmonid fishes. The addition of $Ca^{2+}$ conferred motility to the trout sperm that were immobilized by external $K^+$ and other alkaline metals, $Rb^+$ and $Cs^{2+}$, suggesting the participation of external $Ca^{2+}$ in the initiation of sperm motility. L-type $Ca^{2+}$ channel blockers such as nifedipine, nimodipine, and FS-2 inhibited the motility, but N-type $Ca^{2+}$ channel blocker, w-conotoxin MvIIA, did not. On the other hand, the membrane hyperpolarization and cAMP synthesis were suppressed by $Ca^{2+}$ channel blockers, nifedipine, and trifluoroperazine. Furthermore, these suppressions were relieved by the addition of $K^+$ ionophore, valinomycin. Inhibitors of calmodulin, such as W-7, trifluoperazine, and calrnidazol-C1, inhibited the sperm motility, membrane hyperpolarization, and cAMP synthesis. The results suggest that $Ca^{2+}$ influx through $Ca^{2+}$ channels that are sensitive to specific $Ca^{2+}$ channel blockers and calmodulin participate in the changes of membrane potential, leading to synthesis of cAMP in the cell signaling for the initiation of trout sperm motility.