• Biomolecules & Therapeutics
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• v.26 no.6
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• pp.546-552
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• 2018

A comprehensive collection of proteins senses local changes in intracellular $Ca^{2+}$ concentrations ($[Ca^{2+}]_i$) and transduces these signals into responses to agonists. In the present study, we examined the effect of sphingosine-1-phosphate (S1P) on modulation of intracellular $Ca^{2+}$ concentrations in cat esophageal smooth muscle cells. To measure $[Ca^{2+}]_i$ levels in cat esophageal smooth muscle cells, we used a fluorescence microscopy with the Fura-2 loading method. S1P produced a concentration-dependent increase in $[Ca^{2+}]_i$ in the cells. Pretreatment with EGTA, an extracellular $Ca^{2+}$ chelator, decreased the S1P-induced increase in $[Ca^{2+}]_i$, and an L-type $Ca^{2+}$-channel blocker, nimodipine, decreased the effect of S1P. This indicates that $Ca^{2+}$ influx may be required for muscle contraction by S1P. When stimulated with thapsigargin, an intracellular calcium chelator, or 2-Aminoethoxydiphenyl borate (2-APB), an $InsP_3$ receptor blocker, the S1P-evoked increase in $[Ca^{2+}]_i$ was significantly decreased. Treatment with pertussis toxin (PTX), an inhibitor of $G_i$-protein, suppressed the increase in $[Ca^{2+}]_i$ evoked by S1P. These results suggest that the S1P-induced increase in $[Ca^{2+}]_i$ in cat esophageal smooth muscle cells occurs upon the activation of phospholipase C and subsequent release of $Ca^{2+}$ from the $InsP_3$-sensitive $Ca^{2+}$ pool in the sarcoplasmic reticulum. These results suggest that S1P utilized extracellular $Ca^{2+}$ via the L type $Ca^{2+}$ channel, which was dependent on activation of the $S1P_4$ receptor coupled to PTX-sensitive $G_i$ protein, via phospholipase C-mediated $Ca^{2+}$ release from the $InsP_3$-sensitive $Ca^{2+}$ pool in cat esophageal smooth muscle cells.

• The Korean Journal of Physiology
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• v.27 no.1
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• pp.93-105
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• 1993

The present study was performed to investigate the properties of ionic currents elicited by voltage pulses in the unfertilized eggs of mouse and hamster by using the whole cell voltage clamp techniques and to find out if there are any differences in properties between eggs of the two rodents. In addition, the modulatory effect of G proteins and protein kinase C (PKC) on the ionic channels were observed. The inward current in hamster eggs was shown to be due to $Ca^{2+}\;current\;(i_{ca})$). The current voltage relations of these currents in hamster egg were analogous to those in mouse eggs. The amplitude of $i_{ca}$ in the hamster egg was larger than that in the mouse egg ($-3.12{\pm}1.07\;nA\;vs.\;-1.71{\pm}0.71\;nA,\;mean{\pm}\;SD$). These results suggest that the $Ca^{2+}$ channels in both kinds of eggs have similar channel properties but their density, and/or conduct ance per unit area is higher in hamster eggs than in mouse eggs. Outward currents in eggs of both mouse and hamster were carried by $K^+$. In hamster eggs, they appeared to comprise at least two components; a transient outward component ($i_{to}$) and a steady state component ($i_{\infty}.$ The $i_{to}$ was found to be dependent on intracellular $Ca^{2+}$ concentration; whereas on the other hand $i_{\infty}\;was\;Ca^{2+}$-independent. $Ca^{2+}$ currents were increased in eggs treated with GTP (or $GTP{\gamma}S$) or fluoroaluminate ($AIF_4^-$). In the hamster egg these increments were antagonized by GDP (or $GDP{\beta}S$) application. In contrast to the enhancement of $i_{ca},\;i_k$ was reduced following GTP (or $GTP{\gamma}S$) perfusion in mouse eggs. The transient component ($i_{to}$) in hamster eggs was increased by adding GTP but decreased by phorbol ester, TPA or dioctanoyl glycerol (DOG). Simultaneous application of $GTP{\gamma}S$ and DOG suppressed $i_{to}$ more effectively than a single application or DOG or TPA. From the above results, we have shown that ionic currents elicited by voltage pulses existed in the unfertilized eggs of mouse and hamster. There are at least two types of currents, $i_{ca}\;and\;i_k$ in mouse eggs, while three types, $i_{ca},\;Ca^{2+}$-dependent $i_k$ and $Ca^{2+}$-independent $i_k$ exist in hamster eggs. ionic channels in these eggs may be regulated either directly by GTP and PKC or indirectly by the substances linked with GTP and PKC.

• Proceedings of the PSK Conference
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• 2003.10b
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• pp.128.1-128.1
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• 2003

VR1, a capsaicin receptor, is now known to playa major role in mediating inflammatory thermal nociception. Although the physiological role or biophysical properties of VR1 are known, its activation mechanisms by ligands are poorly understood. Here, we show that VR1 requires phosphorylation by $Ca^{2+}$-calmodulin-dependent kinase II (CaMKII) for its activation by capsaicin. In contrast, dephosphorylation by calcineurin, leads to desensitization of the receptor. Point mutation of VR1 at two putative consensus sites for CaMKII fails to elicit capsaicin-sensitive currents with concomitant reduction in phosphorylation of VR1 in vivo. (omitted)

• Journal of fish pathology
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• v.9 no.1
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• pp.41-51
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• 1996

The present study was undertaken to investigate the physiological characteristics of the adrenergic responses in the tilapia dorsal aorta. Epinephrine, norepinephrine, clonidine and methoxamine in the presence of propranolol($3{\times}10^{-6}$M), induced only endothelium-independent and concentration-dependent vasocontractions in tilapia dorsal aorta. The rank order of potency of adrenergic agonists inducing vasocontraction was epinephrine>norepinephrine>phenylephrine>clonidine>ethoxamine, Yohimbine produced a parallel shift of the concentration-vascontraction curves of epinephrine, norepinephrine, phenylephrine and clonidine to the right, while prazosin depressed the maximum responses of epinephrine and norepinephrine. Calcium-free physiological solution and verapamil markedly reduced epinephrine or norepinephrine-induced vasocontractions. These results suggest that a-adrenergic agonists produce only on endothelium-inedpenent casoconstrictions in tilapia dorsal aorta and these effect of a-adrenergic agonists, which might be associated with both calcium release from intracellular stores and calcium influx through voltage-dependent calcium channel.

• Journal of Life Science
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• v.17 no.8 s.88
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• pp.1053-1062
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• 2007

In the present work, we show that tamoxifen(Tam)-induced cytotoxicity is due to the mitochondrial-dependent pathway triggered by the intracellular $Ca^{2+}$ increase in MCF-7 human breast cancer cells. Tam induced the intracellular $Ca^{2+}$ increase. According to the experimental results with $Ca^{2+}$ channel blockers, Tam-induced $Ca^{2+}$ uptake seemed to depend on the voltage-sensitive $Ca^{2+}$ channel at the early stage, but at later stages the intracellular $Ca^{2+}$ increases are more likely due partly to the release of stored $Ca^{2+}$ and partly to the capacitative $Ca^{2+}$ or other entry pathways. Tam-induced $Ca^{2+}$ increase led to the release of cytochrome c from mitochondria into the cytosol and the change of mitochondrial membrane potential. In MCF-7 cells, caspase-7 plays a key role in the downstream of apoptosis because caspase-3 is absent. In the cells treated with Tam, caspase-7 cleavage was increased almost two-fold. There was no marked alteration in the level of anti-apoptotic Bcl-2 protein; however, the cells showed increased expression of pro-apoptotic Bax protein more than two-fold in response to Tam. These results imply that the apoptotic signaling pathway activated by Tam is likely to be mediated via the mitochondrial-dependent pathway.

• Proceedings of the Korean Biophysical Society Conference
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• 1999.06a
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• pp.52-52
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• 1999

Inactivation of N-type calcium current has been reported to be voltage dependent (Jones ＆ Marks, 1989) and $Ca^{2＋}$ dependent(Cox ＆ Dunlap, 1994). We examined inactivation by recording currents from the same cell both in [B $a^{2＋}$]$_{o}$ and [C $a^{2＋}$]$_{o}$ in rat sympathetic neurons. With 11 mM internal EGTA, fractional inactivation[l-(current amplitude at the end of 5 sec pulse/peak current amplitude [1-(current amplitude at the end of 5 sec pulse/peak current amplitude)] was larger in $Ca^{2+}$(0.80$\pm$0.07) than in $Ba^{2+}$(0.69$\pm$0.10)(n=31, p<0.001), but the current traces were nicely fitted with two exponential components both in $Ba^{2+}$ and $Ca^{2+}$.(omitted)ted)ted)

• The Korean Journal of Physiology
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• v.25 no.2
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• pp.159-170
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• 1991

In the rabbit renal artery, mechanisms of contraction by sodium depletion were investigated. The helical strips of isolated renal artery were immersed in the Tris-buffered salt solution. The contractions were recorded isometrically using a strain-gauge transducer. Na-free solution (Na was substituted by Li, choline or sucrose) produced contractions which were dependent on the nature of the Na substitutes. Na-free solution (choline) produced the contraction in ouabain-pretreated artery (Na loaded artery) even in the presence of verapamil. The amplitude of the contraction was dependent on the duration of the pretreatment with ouabain $(10\;^5M)$. Monensin potentiated the effect of ouabain on the contraction. Removal of Ca from bathing solution abolished the contraction and the substitution of Sr for Ca produced the contraction. Divalent cations such as Mg, Mn blocked the depolarization-induced contraction, while they had little effect on the Na-free contraction in Na loaded artery. These results suggest that the contraction induced by Na removal is dependent on the cellular Na content and may be caused by Ca influx via the Na-Ca exchange carrier.

• 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.24 no.2
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• pp.293-303
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• 1990

The contractile action of barium $(Ba^{2+})$ was investigated in the arterial strip of rabbit renal artery. The helical strip of isolated renal artery was immersed in the Tris-buffered Tyrode's solution equilibrated with 100% $O_2$ at $37^{\circ}C$ and its isometric tension was measured. $Ba^{2+}-induced$ contraction of arterial strip was dose-dependent and its maximal tension corresponded to $92.1{\pm}4.5%$ of tension by $K^+(100\;mM)$. $Ba^{2+}-induced$ contraction did not show the tachyphylactic phenomenon in the normal Tyrode's solution. $Ba^{2+}$ induced the tonic contraction in the $Ca^{2+}-free$ tyrode's solution and that was increased by the extracellula addition of $Ca^{2+}$. During the repeated exposure of the same dose of $Ba^{2+}\;(10\;mM)$ in the $Ca^{2+}-free$ Tyrode's solution, $Ba^{2+}-induced$ contraction was progressively decreased. Even though the intracellular NE-and caffeine-sensitive $Ca^{2+}$ was depleted, $Ba^{2+}$ induced the tonic contraction. After the pretreatment of lanthnum or verapamil, $Ba^{2+}$ did not induce contraction. $Ba^{2+}-induced$contraction was suppressed by extracellular $K^+$ in the normal Tyrode's solution and that was dependent on $K^+$ concentration. Suppressive effect of $K^+\;(14\;mM)$ on the $Ba^{2+}-induced$ contraction was also dependent on the intracellular $Ca^{2+}$ concentration. From the above resuts, it is suggested that $Ba^{2+}$ activate indirectly the contractile process by promoting the mobilization of intracellular $Ca^{2+}$ and the influx of extracellular $Ca^{2+}$. It is also suggested that action of $Ba^{2+}$ on the $Ca^{2+}-activated$ $K^+$ channel can result in the depolarization of cell membrane in the rabbit renal artery.

• The Korean Journal of Physiology
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• v.23 no.2
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• pp.263-275
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• 1989

Mechanical contractions and electrical activities of the fundic longitudinal and antral circular muscle fibers were investigated in order to elucidate topical differences of gastric motility. K-induced contracture was produced by exposure of muscle strips to high K Tyrode solution. Membrane potential and mechanical contraction were simultaneously recorded by conventional glass microelectrode method and single sucrose-gap technique. All experiments were performed in tris-buffered Tyrode solution which was aerated with $100%\;O_2\;and\;kept\;35^{\circ}C$. The results obtained were as follows: 1) The resting membrane potential of circular muscle cells in the antral region was about 10 mV more negative than that in the fundic region. 2) The membrane potentials decreased almost linearly as the extracellular KCI concentration was increased both in antral circular muscle cells and in fundic longitudinal muscle cells. 3) The thresholdal K concentration of K-contracture was 15 mM (membrane potential, -48 mV) for the antral circular muscle strip and 20 mM for the fundic longitudinal muscle cells. 4) The ratio of membrane permeability coefficient for $Na^+\;and\;K^+,\;P_{Na}/P_K\;({\alpha})$ was 0.065 for antral circular muscle cells and was 0.108 for fundic longitudinal muscle cells. 5) K-contracture of antral and fundic smooth muscle strips showed the contracture composed of phasic and tonic components. The amplitude of the phasic component increased sigmoidally in a dose-dependent manner, whereas that of the tonic component was maximal at a concentration of 40 mM KCI and at the concentrations above or below 40 mM KCI the amplitude was reduced. 6) The inverse relationship between the amplitude of tonic component and extracellular KCI concentration in the range of 40 to 150 mM KCI was more prominent in the antral circular muscle strip than in the fundic longitudinal muscle strip, where the amplitude of the tonic component decreased less steeply and was maintained higher at the same high K concentrations. 7) The tonic component was totally dependent on the external $Ca^{2+}$ and completely abolished by verapamil, while tile phasic component was far less dependent on the external $Ca^{2+}$ and partially suppressed by verapamil. From the above results, the following conclusions could be made. 1) The phasic component of K-contracture is produced both by intracellular $Ca^{2+}$ mobilization and by $Ca^{2+}$-influx from outside, while the tonic component is generated and maintained by the $Ca^{2+}-influx$ through the potential-dependent $Ca^{2+}$ channel. 2) The mechanism of reducing the free $Ca^{2+}$ concentration in the myoplasm seems to be more developed in the antral circular muscle than in the fundic longitudinal muscle. 3) The lower resting membrane potential of the fundic longitudinal muscle cell reflects a relatively high $P_{Na}/P_K$ ratio of about 0.108.