• Journal of Chest Surgery
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• v.18 no.1
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• pp.1-6
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• 1985

Isolated sinus node cells of the rabbit were used to assess the effects of extracellular Na, K, Ca and Mg concentrations on cardiac pacemaker activity. With intracellular glass micro-electrodes spontaneous action potentials of SA node were recorded and the effects of various ions and their blockers were analyzed in terms of the cycle length, the amplitude and the duration of action potentials, the results obtained were as follows. 1. Sodium reduction [up to 30%] decreased the amplitude of action potential and lengthened the cycle length. TTX, specific blocker of Na channel slightly lengthened the cycle length. 2. Increasing potassium ion concentration, the duration of action potential decreased and the frequency increased in 6mM, however, spontaneous action potential was stopped in 24 mM. Barium ion known to be decreasing K conductance increased the duration of action potential but no significant change in the cycle length was noticed. 3. Calcium ion has shortening effect on the duration and the cycle length of action potential but not with dose-dependent manner. Cadmium ion .[0.02mM] lengthened cycle length and the duration of action potential. 4. Increasing the concentration of magnesium ion the cycle length was lengthened, significantly.

• Journal of Korean Neurosurgical Society
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• v.42 no.3
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• pp.205-210
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• 2007

Objective : Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels mediate the hyperpolarization-activated currents (Ih) that participate in regulating neuronal membrane potential and contribute critically to pacemaker activity, promoting synchronization of neuronal networks. However, distinct regional and cellular localization of HCN channels in the brain have not been precisely defined. Aim of this study was to verify the precise cellular location of HCN1 channels in rat cerebellum to better understand the physiological role these channels play in synaptic transmission between CNS neurons. Methods : HCN1 expression in rat brain was analyzed using immunohistochemistry and electron-microscopic observations. Postsynaptic density-95 (PSD-95), otherwise known as locating and clustering protein, was also examined to clarify its role in the subcellular location of HCN1 channels. In addition, to presume the binding of HCN1 channels with PSD-95, putative binding motifs in these channels were investigated using software-searching method. Results : HCN1 channels were locally distributed at the presynaptic terminal of basket cell and exactly corresponded with the location of PSD-95. Moreover, nine putative SH3 domain of PSD-95 binding motifs were discovered in HCN1 channels from motif analysis. Conclusion : Distinct localization of HCN1 channels in rat cerebellum is possible, especially when analyzed in conjunction with the SH3 domain of PSD-95. Considering that HCN1 channels contribute to spontaneous rhythmic action potentials, it is suggested that HCN1 channels located at the presynaptic terminal of neurons may play an important role in synaptic plasticity.

• The Korean Journal of Physiology
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• v.6 no.2
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• pp.31-37
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• 1972

The right cervical vagus nerve was electrically stimulated for 30 sec, and 30 minutes recording cardiac rate responses and electrocardiogram. The main purposes of the present experiment are to determine effect of stimulation frequency on the maintenance of cardiac rate responses and to determine recovery time of sinus rhythm after asystole period followed by idioventricular rhythm during prolonged electrical stimulation of the vagus, and the optimal stimulation parameters for vagal stimulation were studied as well. The results obtained are summarized as follows: 1. The maximum negative chrontropic responses were obtained with the following ranges of electrical parameters. Intensity: 3V-7V, Frequency: 20/sec-60/sec, and pulse duration: 5 msec-20 msec. 2. Compared with the responses from sympathetic effectors, cardiac rate responses to electrical stimulation of vagus nerve were well maintained with all stimulation frequencies. 3. At all stimulation frequencies except 20/sec, sinus node started to take over primary pacemaker activity when cardiac rates were restored to about 38-40/min. 4. It was indicated that upper limit of idioventricular rhythm does not exceed 38-40/min. 5. With the stimulation parameter set of 20/sec-5 msec-3 V, sinus rhythm did not appear during 30 minutes of stimulation period. Therefore, this electrical parameter set appears to be optimal for elicitation of prolonged and maximum cardiac rate responses by vagal stimulation.

• Journal of Chest Surgery
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• v.16 no.2
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• pp.199-212
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• 1983

The inhibition/influences of adenine compounds on the heart have been described repeatedly by many investigators, since the first report by Druny and Szent-Gyorgyi [1929]. These studies have shown that adenosine and adenine nucleotides have an over-all effect similar to that of acetylcholine [ACh] by slowing and weakening the heartbeat. The basic cellular and membrane events underlying the inhibitory action of adenosine on sinus rate, however, are not well understood. Furthermore, the physiological role of adenosine in regulation of the heartbeat remains still to be elucidated. Therefore, this study was undertaken in order to examine the response of rabbit SA node to adenosine and to compare the response to that of ACh. Isolated SA node preparation, whole atrial pair, or left atrlal strip was used in each experiment. Action potentials of SA node were recorded through the intracellular glass microelectrodes, which were filled with 3M KCI and had resistance of 30-50 M. All experiments were performed in a bicarbonate-buffered Tyrode solution which was aerated with 3% $CO_2-97%$ $O_2$ gas mixture and kept at $35^{\circ}C$. Spontaneous firing rate of SA node at 35C [Mean + SEM, n=16] was 154 + 3.3 beats/min. The parameters of action potentials were: maximum astolic potential [MDP], -731.7mV: overshoot [OS], 9 + 1.4mV; slope of pacemaker potential [SPP], 94 3.0mV/sec.Adenosine suppressed the firing rate of SA node in a dose dependent manner. This inhibitory effect appeared at the concentration of $10^{-6}M$ and was potentiated in parallel with the increase in adenosine concentration. Changes in action potential by adenosine were dose-dependent increase of MDP and decrease of SPP until $10^{-4}$. Above this concentration, however, the amplitude of action potential decreased markedly due to the simultaneous decrease of both MDP and OS. All these effects of adenosine were not affected by pretreatment of atropine [2mg/l] and propranolol [$5{\times}10^{-6}M$]. ACh [$10^{-6}M$] responses on action potential were similar to those of adenosine by increasing MDP and decreasing SPP. These effects of ACh disappeared by pretreatment of atropine [2mg/1]. Inhibition/effects of adenosine and ACh on sinus rate were enhanced synergistically with the simultaneous administration of adenosine and ACh. Marked decrease of overshoot potential was the most prominent feature on action potential. Dipyridamole [DPM], which is known to block the adenosine transport across cell membrane, definitely potentiated the action of adenosine . Adenosine suppressed the sinus rate and atrial contractility in the same dosage range, even in the reserpinized preparation. Above` results suggest that adenosine suppresses pacemaker activity, like ACh, by acting directly on the membrane of SA node, increasing MDP and decreasing SPP.

• Molecules and Cells
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• v.42 no.4
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• pp.301-312
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• 2019

Post-transcriptional regulation underlies the circadian control of gene expression and animal behaviors. However, the role of mRNA surveillance via the nonsense-mediated mRNA decay (NMD) pathway in circadian rhythms remains elusive. Here, we report that Drosophila NMD pathway acts in a subset of circadian pacemaker neurons to maintain robust 24 h rhythms of free-running locomotor activity. RNA interference-mediated depletion of key NMD factors in timeless-expressing clock cells decreased the amplitude of circadian locomotor behaviors. Transgenic manipulation of the NMD pathway in clock neurons expressing a neuropeptide PIGMENT-DISPERSING FACTOR (PDF) was sufficient to dampen or lengthen free-running locomotor rhythms. Confocal imaging of a transgenic NMD reporter revealed that arrhythmic Clock mutants exhibited stronger NMD activity in PDF-expressing neurons than wild-type. We further found that hypomorphic mutations in Suppressor with morphogenetic effect on genitalia 5 (Smg5) or Smg6 impaired circadian behaviors. These NMD mutants normally developed PDF-expressing clock neurons and displayed daily oscillations in the transcript levels of core clock genes. By contrast, the loss of Smg5 or Smg6 function affected the relative transcript levels of cAMP response element-binding protein B (CrebB) in an isoform-specific manner. Moreover, the overexpression of a transcriptional repressor form of CrebB rescued free-running locomotor rhythms in Smg5-depleted flies. These data demonstrate that CrebB is a rate-limiting substrate of the genetic NMD pathway important for the behavioral output of circadian clocks in Drosophila.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.2
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• pp.81-90
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• 2000

The types of $K^+$ channel which determine the pattern of spontaneous action potential (SAP) were investigated using whole-cell variation of patch clamp techniques under current- and voltage-clamp recording conditions in rat clonal pituitary $GH_3$ cells. Heterogeneous pattern of SAP activities was changed into more regular mode with elongation of activity duration and afterhyperpolarization by treatment of TEA (10 mM). Under this condition, exposure of the class III antiarrhythmic agent E-4031 $(5\;{\mu}M)$ to $GH_3$ cells hardly affected SAP activities. On the other hand, the main $GH_3$ stimulator thyrotropin-releasing hormone (TRH) still produced its dual effects (transient hyperpolarization and later increase in SAP frequency) in the presence of TEA. However, addition of $BaCl_2$ (2 mM) in the presence of TEA completely blocked SAP repolarization process and produced membrane depolarization in all tested cells. This effect was observed even in TEA-untreated cells and was not mimicked by higher concentration of TEA (30 mM). Also this barium-induced membrane depolarization effect was still observed after L-type $Ca^{2+}$ channel was blocked by nicardipine $(10\;{\mu}M).$ These results suggest that barium-sensitive current is important in SAP repolarization process and barium itself may have some depolarizing effect in $GH_3$ cells.

• Molecules and Cells
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• v.20 no.3
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• pp.435-441
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• 2005

Classical transient receptor potential channels (TRPCs) are thought to be candidates for the nonselective cation channels (NSCCs) involved in pacemaker activity and its neuromodulation in murine stomach smooth muscle. We aimed to determine the role of TRPC4 in the formation of NSCCs and in the generation of slow waves. At a holding potential of -60 mV, $50{\mu}M$ carbachol (CCh) induced $I_{NSCC}$ of amplitude [$500.8{\pm}161.8pA$ (n = 8)] at -60 mV in mouse gastric smooth muscle cells. We investigated the effects of commercially available antibodies to TRPC4 on recombinant TRPC4 expressed in HEK cells and CCh-induced NSCCs in gastric smooth muscle cells. TRPC4 currents in HEK cells were reduced from $1525.6{\pm}414.4pA$ (n = 8) to $146.4{\pm}83.3pA$ (n = 10) by anti-TRPC4 antibody and $I_{NSCC}$ amplitudes were reduced from $230.9{\pm}36.3pA$ (n = 15) to $49.8{\pm}11.8pA$ (n = 9). Furthermore, $I_{NSCC}$ in the gastric smooth muscle cells of TRPC4 knockout mice was only $34.4{\pm}10.4pA$ (n = 8) at -60 mV. However, slow waves were still present in the knockout mice. Our data suggest that TRPC4 is an essential component of the NSCC activated by muscarinic stimulation in the murine stomach.