• The Korean Journal of Physiology and Pharmacology
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• 제5권2호
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• pp.147-156
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• 2001

It has been proposed that $Ca^{2+}-activated$ K $(K_{Ca})$ channels play an essential role in vascular tone. The alterations of the properties of coronary $K_{Ca}$ channels have not been studied as a possible mechanism for impaired coronary reserve in cardiac hypertrophy. The present studies were carried out to determine the properties of coronary $K_{Ca}$ channels in normal and hypertrophied hearts. These channels were measured from rabbit coronary smooth muscle cells using a patch clamp technique. The main findings of the present study are as follows: (1) the unitary current amplitudes and the slope conductance of coronary $K_{Ca}$ channels were decreased without changes of the channel kinetics in isoproterenol-induced cardiac hypertrophy; (2) the sensitivity of coronary $K_{Ca}$ channels to the changes of intracellular concentration of $Ca^{2+}$ was reduced in isoproterenol-induced cardiac hypertrophy. From above results, we suggest for the first time that the alteration of $K_{Ca}$ channels are involved in impaired coronary reserve in isoproterenol-induced cardiac hypertrophy.

• The Korean Journal of Physiology and Pharmacology
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• 제9권1호
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• pp.37-43
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• 2005

Our previous report demonstrated that chick myoblasts are equipped with $Ca^{2+}$-permeable stretchactivated channels and $Ca^{2+}-activated$ potassium channels ($K_{Ca}$), and that hyperpolarization-induced by $K_{Ca}$ channels provides driving force for $Ca^{2+}$ influx through the stretch-activated channels into the cells. Here, we showed that acetylcholine (ACh) also hyperpolarized the membrane of cultured chick myoblasts, suggesting that nicotinic acetylcholine receptor (nAChR) may be another pathway for $Ca^{2+}$ influx. Under cell-attatched patch configuration, ACh increased the open probability of $K_{Ca}$ channels from 0.007 to 0.055 only when extracellular $Ca^{2+}$ was present. Nicotine, a nAChR agonist, increased the open probability of $K_{Ca}$ channels from 0.008 to 0.023, whereas muscarine failed to do so. Since the activity of $K_{Ca}$ channel is sensitive to intracellular $Ca^{2+}$ level, nAChR seems to be capable of inducing $Ca^{2+}$ influx. Using the $Ca^{2+}$ imaging analysis, we were able to provide direct evidence that ACh induced $Ca^{2+}$ influx from extracellular solution, which was dramatically increased by valinomycin-mediated hyperpolarization. In addition, ACh hyperpolarized the membrane potential from $-12.5{\pm}3$ to $-31.2{\pm}5$ mV by generating the outward current through $K_{Ca}$ channels. These results suggest that activation of nAChR increases $Ca^{2+}$ influx, which activates $K_{Ca}$ channels, thereby hyperpolarizing the membrane potential in chick myoblasts.

• The Korean Journal of Physiology and Pharmacology
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• 제12권2호
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• pp.51-58
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• 2008

Cardiac fibroblasts constitute one of the largest cell populations in the heart, and contribute to structural, biochemical, mechanical and electrical properties of the myocardium. Nonetheless, their cardiac functions, especially electrophysiological properties, have often been disregarded in studies. $Ca^{2+}$-activated $K^+\;(K_{Ca})$ channels can control $Ca^{2+}$ influx as well as a number of $Ca^{2+}$-dependent physiological processes. We, therefore, attempted to identify and characterize $K_{Ca}$ channels in rat Cardiac fibroblasts. First, we showed that the cells cultured from the rat ventricle were cardiac fibroblasts by immunostaining for discoidin domain receptor 2 (DDR-2), a specific fibroblast marker. Secondly, we detected the expression of various $K_{Ca}$ channels by reverse transcription polymerase chain reaction (RT-PCR), and found all three family members of $K_{Ca}$ channels, including large conductance $K_{Ca}$ (BK-${\alpha}1-\;and\;-{\beta}1{\sim}4$subunits), intermediate conductance $K_{Ca}$ (IK), and small conductance $K_{Ca}$ (SK$1{\sim}4$ subunits) channels. Thirdly, we recorded BK, IK, and SK channels by whole cell mode patch clamp technique using their specific blockers. Finally, we performed cell proliferation assay to evaluate the effects of the channels on cell proliferation, and found that the inhibition of IK channel increased the cell proliferation. These results showed the existence of BK, IK, and SK channels in rat ventricular fibroblasts and involvement of IK channel in cell proliferation.

• BMB Reports
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• 제44권10호
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• pp.635-646
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• 2011

Due to its high external and low internal concentration the $Ca^{2+}$ ion is used ubiquitously as an intracellular signaling molecule, and a great many $Ca^{2+}$-sensing proteins have evolved to receive and propagate $Ca^{2+}$ signals. Among them are ion channel proteins, whose $Ca^{2+}$ sensitivity allows internal $Ca^{2+}$ to influence the electrical activity of cell membranes and to feedback-inhibit further $Ca^{2+}$ entry into the cytoplasm. In this review I will describe what is understood about the $Ca^{2+}$ sensing mechanisms of the three best studied classes of $Ca^{2+}$-sensitive ion channels: Large-conductance $Ca^{2+}$-activated $K^+$ channels, small-conductance $Ca^{2+}$-activated $K^+$ channels, and voltage-gated $Ca^{2+}$ channels. Great strides in mechanistic understanding have be made for each of these channel types in just the past few years.

• Asian-Australasian Journal of Animal Sciences
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• 제15권7호
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• pp.949-956
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• 2002

There are several physiological and pharmacological evidences indicating that opening of voltage dependent $Ca^{2+}$ channels play a critical role in induction of acrosome reaction in mammalian sperm. We determined the intracellular free $Ca^{2+}$ concentration in ejaculated goat sperm using a fluorescent, $Ca^{2+}$-specific probe, Fura2/AM, after the suspension of sperm in KRB medium, capable of sustaining capacitation and the acrosome reaction. We used nifedipine, D-600 and diltiazem, the $Ca^{2+}$ channel antagonists belonging to the classes of dihydropyridines, phenylalkylamines and benzothiazepines, to investigate the possibility that L-type voltage gated $Ca^{2+}$ channels play a role in the progesterone-stimulated exocytotic response. Progesterone promoted a rise in intracellular $Ca^{2+}$ in goat sperm and addition of nifedipine (100 nM) just prior to progesterone induction, significantly inhibited both intracellular $Ca^{2+}$ rise and exocytosis suggesting that $Ca^{2+}$ channels are involved in the process. However, the intracellular $Ca^{2+}$ increase during the process of capacitation was not affected with the addition of nifedipine suggesting a role of focal channel for $Ca^{2+}$ during capacitation. Studies using monensin and nigericin, two monovalent cation ionophores showed that an influx of $Na^+$ also may play a role in the opening of $Ca^{2+}$ channels. These results strongly suggests that the entry of $Ca^{2+}$ channels with characteristics similar to those of L-type, voltage-sensitive $Ca^{2+}$ channels found in cardiac and skeletal muscle, is a crucial step in the sequence of events leading to progesterone induced acrosome reaction in goat sperm.

• The Korean Journal of Physiology and Pharmacology
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• 제11권5호
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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.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 2003년도 정기총회 및 학술발표회
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• pp.44-44
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• 2003

$BK_{Ca}$ channels were suggested to contain one or more domains of the ‘regulator of K+ conductance’(RCK) in their cytosolic carboxyl termini (Jiang et al.2001). It was also shown that the RCK domain in mammalian $BK_{Ca}$ channels might sense the intracellular $Ca^{2+}$ with a low affinity (Xia et al. 2002). We aligned the amino acid sequence of the $\alpha$-subunit of rat $BK_{Ca}$ channels (rSlo) with known RCK domains and identified a second region exhibiting about 50％ homology. This putative domain, RCK2, contains the characteristic amino acids conserved in other RCK domains. We wondered whether this second domain is involved in the domain-domain interaction and the gating response to intracellular $Ca^{2+}$ for rSlo channel, as revealed in the structure of RCK domain of E. coli channel (Jiang et al.2001). In order to examine the possibility, site-directed mutations were introduced into the RCK2 domain of rSlo channel and the mutant channels were expressed in Xenopus oocytes for functional studies. One of such mutation, G772D, in the putative nucleotide-binding domain resulted in the enhanced $Ca^{2+}$ sensitivity and the channel gating of rSlo channel. These results suggest that this region of $BK_{Ca}$ channels is important for the channel gating and may form an independent domain in the cytosolic region of $BK_{Ca}$ channels. In order to obtain the mechanistic insights of these results, G772 residue was randomly mutagenized by site-directed mutagenesis and total 17 different mutant channels were constructed. We are currently investigating these mutant channels by electrophysiological techniques.ical techniques.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 2001년도 학술 발표회 진행표 및 논문초록
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• pp.36-36
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• 2001

Small conductance $Ca^{2＋}$-activated $K^{+}$ channels (or S $K_{Ca}$ channels) are a group of $K^{＋}$-selective ion channels activated by sub-micromolar concentrations of intracellular $Ca^{2＋}$ independent of membrane voltage. We expressed a cloned S $K_{Ca}$ channel, rSK2, in Xenopus oocytes and investigated the monovalent cation selectivity of the channels. We have used site-directed mutagenesis and macro-channel recordings to identify amino acid residues influencing the ion selectivity.(omitted)d)

• The Korean Journal of Physiology and Pharmacology
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• 제21권2호
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• pp.259-265
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• 2017

Excessive influx and the subsequent rapid cytosolic elevation of $Ca^{2+}$ in neurons is the major cause to induce hyperexcitability and irreversible cell damage although it is an essential ion for cellular signalings. Therefore, most neurons exhibit several cellular mechanisms to homeostatically regulate cytosolic $Ca^{2+}$ level in normal as well as pathological conditions. Delayed rectifier $K^+$ channels ($I_{DR}$ channels) play a role to suppress membrane excitability by inducing $K^+$ outflow in various conditions, indicating their potential role in preventing pathogenic conditions and cell damage under $Ca^{2+}$-mediated excitotoxic conditions. In the present study, we electrophysiologically evaluated the response of $I_{DR}$ channels to hyperexcitable conditions induced by high $Ca^{2+}$ pretreatment (3.6 mM, for 24 hours) in cultured hippocampal neurons. In results, high $Ca^{2+}$-treatment significantly increased the amplitude of $I_{DR}$ without changes of gating kinetics. Nimodipine but not APV blocked $Ca^{2+}$-induced $I_{DR}$ enhancement, confirming that the change of $I_{DR}$ might be targeted by $Ca^{2+}$ influx through voltage-dependent $Ca^{2+}$ channels (VDCCs) rather than NMDA receptors (NMDARs). The VDCC-mediated $I_{DR}$ enhancement was not affected by either $Ca^{2+}$-induced $Ca^{2+}$ release (CICR) or small conductance $Ca^{2+}$-activated $K^+$ channels (SK channels). Furthermore, PP2 but not H89 completely abolished $I_{DR}$ enhancement under high $Ca^{2+}$ condition, indicating that the activation of Src family tyrosine kinases (SFKs) is required for $Ca^{2+}$-mediated $I_{DR}$ enhancement. Thus, SFKs may be sensitive to excessive $Ca^{2+}$ influx through VDCCs and enhance $I_{DR}$ to activate a neuroprotective mechanism against $Ca^{2+}$-mediated hyperexcitability in neurons.

• The Korean Journal of Physiology and Pharmacology
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• 제2권2호
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• pp.133-145
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• 1998

$Ca^{2+}-signals$ in endothelial cells are determined by release from intracellular stores and entry through the plasma membrane. In this review, the nature of $Ca^{2+}$ entry and mechanisms of its control are reviewed. The following ion channels play a pivotal role in regulation of the driving force for $Ca^{2+}$ entry: an inwardly rectifying $K^+$ channel, identified as Kir2.1, a big-conductance, $Ca^{2+}-activated$ $K^+$ channel (hslo) and at least two $Cl^-$ channels (a volume regulated $Cl^-$ channel, VRAC, and a $Ca^{2+}$ activated $Cl^-$ channel, CaCC). At least two different types of $Ca^{2+}$-entry channels exist: 1. A typical CRAC-like, highly selective $Ca^{2+}$ channel is described. Current density for this $Ca^{2+}$ entry is approximately 0.1pA/pF at 0 mV and thus 10 times smaller than in Jurkat or mast cells. 2. Another entry pathway for $Ca^{2+}$ entry is a more non-selective channel, which might be regulated by intracellular $Ca^{2+}$. Although detected in endothelial cells, the functional role of trp1,3,4 as possible channel proteins is unclear. Expression of trp3 in macrovascular endothelial cells from bovine pulmonary artery induced non-selective cation channels which are probably not store operated or failed to induce any current. Several features as well as a characterisation of $Ca^{2+}$-oscillations in endothelial cells is also presented.