Biomedical subjects

Y Habuchi

Publications and source records attributed to Y Habuchi.

At least 37 records · Page 2Linked to original sources

PubMed1996

Regulation by acetylcholine of Ca2+ current in rabbit atrioventricular node cells.

Effects of acetylcholine (ACh) on L-type Ca2+ current (ICa) were examined in isolated atrioventricular (AV) node cells exhibiting spontaneous contractions and pacemaker current (If). ACh at a saturating concentration of 10 microM reduced basal ICa by 48 +/- 6%. The ACh effect was abolished by dialysis with 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), an adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase inhibitor, or guanosine-5'-O-(2-thiodiphosphate). Dialysis with guanosine 3',5'-cyclic monophosphate (cGMP) or NG-monomethyl-L-arginine (L-NMMA) and application of the cGMP-dependent protein kinase inhibitor KT-5823 (1 microM) did not affect ACh inhibition of ICa. Nitric oxide donor 3-morpholinosydnonimine (100 microM) and type III phosphodiesterase (PDE) inhibitor trequinsin (10 nM) enhanced basal ICa by 10-20%, whereas type IV PDE inhibitor Ro-20-1724 (30 microM) together with trequinsin caused a large ICa stimulation comparable to that by 3-isobutyl-1-methylxanthine (IBMX). These findings indicate that ACh inhibits basal ICa primarily by suppressing cAMP synthesis and that these cells have a potent type III and IV PDE activity to determine the basal cAMP concentration. When ICa was stimulated by IBMX (100 microM), the inhibitory effect of ACh was slightly reduced by L-NMMA, cGMP, and methylene blue but not by KT-5823 or Ro-20-1724. ACh hardly inhibited, or even enhanced, IBMX-stimulated Ica when forskolin (3 microM) was coapplied or the IBMX concentration was increased to 500 microM. These findings suggest that cAMP is degraded in the presence of 100 microM IBMX to some extent. Type II PDE, for which IBMX has a relatively high inhibitor constant, seems to contribute partially to the cAMP degradation.

1-Methyl-3-isobutylxanthine↗

PubMed1996

Delineation of premature P waves on four-dimensional electrocardiography, a new display of electrical forces by computer techniques.

This study investigated the feasibility of four-dimensional electrocardiography (4-D ECG), a new display in which the vector loop was rotated and scanned along a timed axis to overcome the shortcomings of vectorcardiography (VCG). The subjects consisted of 38 patients with premature atrial complexes and 30 controls. The orthogonal Frank electrocardiograms were rotated three-dimensionally according to the right-hand rectangular coordinate system and scanned along a timed axis. The P wave delineation score, signifying good agreement with the intraobserver and interobserver variability, was significantly higher in 4-D ECG than those in the orthogonal leads or those on the transverse and frontal projections (P < 0.001). The authors measured the premature P loop areas as viewed from 361 directions. P loop areas were best delineated when viewed from cranial directions of 42.6 +/- 34.0 degrees and from rightward directions of 11.3 +/- 30.7 degrees. Adequate cranial rotation followed by scanning along a timed axis will maximally delineate premature atrial signals and provide comprehensive visualization of electrical forces.

Atrial Premature Complexes↗

PubMed1995

Ethanol inhibition of Ca2+ and Na+ currents in the guinea-pig heart.

The effects of ethanol on L-type Ca2+ and fast Na+ currents (ICa and INa, respectively) were examined using the whole-cell patch-clamp experiments on guinea-pig ventricular cells. At a clinically relevant concentration of 24 mM, ethanol slightly but significantly shortened the action potential duration, and reduced the ICa by 7 +/- 4% (mean +/- S.D.). This concentration of ethanol did not affect INa, but a lethal concentration of ethanol (80 mM) significantly inhibited INa by 13 +/- 5%. The voltage dependence of INa activation was not affected by ethanol, whereas the inhibitions of ICa by 80 mM ethanol and INa by 240 mM were both accompanied by a several mV shift in the channel availability curve toward more negative potentials, suggesting that the channels in the inactivated state are more susceptible to ethanol. The ICa inhibition by ethanol at clinically relevant concentrations could contribute to a negative inotropic effect, action potential shortening and development of arrhythmias, while the pathophysiological significance of ethanol inhibition of INa seems less important.

Action Potentials↗

PubMed1995

Electrophysiological effects of changrolin, an anti-arrhythmic agent derived from Dichroa febrifuga, on guinea-pig and rabbit heart cells.

1. The electrophysiological effects of changrolin (CRL), a Chinese anti-arrhythmic drug derived from a traditional antimalarial plant, were examined using the whole-cell patch-clamp method on single cells isolated from guinea-pig and rabbit hearts. 2. At a clinically relevant concentration of 50 mumol/L changrolin inhibited ICa by 19.3 +/- 6.0% and 17.3 +/- 2.6% in guinea-pig and rabbit ventricular cells, respectively. The voltage-dependent channel availability curve was not affected. The CRL effect was enhanced to a small extent during a repetitive stimulation at 2 Hz. 3. INa was resistant to CRL and the channel availability curve was also unaffected. A small use-dependent inhibition was observed only when the INa was elicited at 5 Hz in the presence of 300 mumol/L CRL. 4. At 50 mumol/L, CRL did not affect the time-independent inward rectifier and the delayed rectifier K+ currents (IK1 and IK, respectively), but inhibited the transient outward current (ITO) by 17.7 +/- 2.4%. Changrolin significantly shortened the action potential duration in both guinea-pig and rabbit ventricular cells. 5. In conclusion, CRL inhibits ICa and ITO but has little effect on INa.

Action Potentials↗

PubMed1995

Decreased sensitivity to beta-adrenergic stimulation of the ventricular cells isolated from the spontaneously hypertensive rat heart.

1. The stimulatory effects of isoproterenol on the L-type Ca2+ current (ICa) were compared between the control (WKY) and hypertensive (SHR) rat heart cells, using the patch-clamp method. 2. The current density and the shape of the current-voltage relationship for ICa were not different between the two groups. However, the maximal percentage increase in response to isoproterenol was smaller in SHR (+91% in SHR and +81% in WKY), and the ED50 was significantly higher in SHR (0.081 mu mol/L in SHR and 0.020 mu mol/L in WKY). IBMX, a potent phosphodiesterase inhibitor, significantly increased the isoproterenol-stimulated ICa in SHR, but not in WKY. These results suggest an impaired cAMP production in SHR heart cells.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Angiotensin II inhibition of L-type Ca2+ current in sinoatrial node cells of rabbits.

The actions of angiotensin II (ANG II) were examined in the spontaneously active cells isolated from the rabbit sinoatrial node, using the nystatin-permeabilized, whole cell, patch-clamp method. At 30 nM, ANG II significantly lowered the spontaneous firing rate of the action potentials from 212 +/- 21 to 172 +/- 32 beats/min, with a concomitant reduction in the action potential amplitude. The voltage-clamp experiments showed that ANG II inhibited the L-type Ca2+ current (ICa) with a dissociation constant (Kd) of approximately 4 nM and a maximal inhibition of 30%. The inhibition was blocked by an AT1-receptor antagonist CV11974. Acetylcholine (ACh) at 10 microM reduced the ICa by 42 +/- 12%, and ANG II did not cause any further inhibition in the presence of ACh. At 100 nM, ANG II reduced the ICa by only 12% in the presence of 2 microM isoproterenol, and a similar inhibition was observed with 0.1 microM ACh. ANG II did not affect the dibutyryl adenosine 3',5'-cyclic monophosphate-stimulated ICa. Protein kinase C activator 12-O-tetra-decanoylphorbol-13-acetate did not mimic ANG II in the effects on ICa, and preincubation of the cells with calphostin C, a protein kinase C inhibitor, did not attenuate the ANG II effect. ANG II exerts a negative chronotropic effect in the pacemaker cells as its direct action through a pathway involving adenosine 3',5'-cyclic monophosphate-dependent protein kinase.

Acetylcholine↗

PubMed1995

Delayed rectifier K+ current in rabbit atrial myocytes.

The role of delayed rectifier K+ current(s) (IK) in rabbit left atrium was examined by applying the whole cell voltage-clamp technique to isolated single myocytes. Right-triangular waveforms, which mimic the shape of atrial action potentials (APs), and selective blockers were used to compare the contribution of IK with other K+ currents to repolarization of the APs. IK measured at 34 degrees C in atrial myocytes was very small; the maximum peak amplitude of the tail current (IK,tail) at -40 mV was approximately 50 pA. The IK,tail was almost abolished in most cells (approximately 80%) by the application of 1 microM E-4031, a class III antiarrhythmic drug. The E-4031-sensitive current recorded with the triangular command wave-form showed strong inward rectification and had a maximum amplitude of approximately 30 pA at -40 mV. Total outward current elicited by triangular command pulses depended strongly on stimulation frequency. The main frequency-dependent component was a Ca(2+)-independent transient K+ current (I(t)). I(t) elicited by triangular pulses at 1 Hz was substantially reduced by 4-aminopyridine (4-AP) at potentials positive to 0 mV but was not changed significantly by 1 microM E-4031; 100 microM E-4031 reduced I(t) by approximately 30%. The shape of the APs which were recorded from a single rabbit atrial cell strongly depended on the pulse frequency. Application of 1 microM E-4031 increased action potential duration (APD) in > 50% of cells examined but had little effect on the resting membrane potential (RMP). Application of 0.1 mM BaCl2 also lengthened APD and reduced RMP by approximately 20 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗

PubMed1995

Does dopamine act on myocardial cells?

We examined the electrophysiological effects of dopamine on the single myocardial cells isolated from the rat and rabbit heart. Dopamine at a concentration of 1 or 10 microM did not affect the L-type Ca2+ current (ICa) or the transient outward current (ITO) in rat ventricular, rabbit atrial, ventricular, and sinoatrial node cells. It did not induce any detectable change in the action potential configuration of the rabbit ventricular cells either. We conclude that dopamine does not directly act on myocardial cells at least in terms of the electrophysiological properties.

Action Potentials↗

PubMed1995

Urinary excretion of free dopamine and digoxinlike substances correlates with endogenous secretion of insulin in normotensive adults, but not in hypertensive subjects.

We investigated whether urinary excretion of free dopamine is related with the humoral factors which affect Na+, K+ ATPase activity in the kidneys. Subjects were 51 adults admitted in a hospital without renal insufficiency: they were divided into normotensive (n = 36, 60 +/- 3 years old, 122 +/- 3/73 +/- 2 mmHg) and hypertensive groups (n = 15, 65 +/- 5 years old, 157 +/- 6/91 +/- 2 mmHg). Urinary excretion of free dopamine was significantly and positively correlated with urinary excretion of C-peptide immunoreactivity of insulin (CPR) (r = 0.451, p = 0.014) in normotensive subjects, but not in hypertensive subjects (r = 0.155, p = 0.668). Urinary excretion of endogenous digoxinlike substances (EDLS) was also significantly and positively correlated with urinary CPR (r = 0.500, p = 0.006) in normotensive subjects, but not in hypertensive subjects (r = 0.275, p = 0.363). In normotensive subjects, urinary excretion of free dopamine and EDLS may be regulated at least in part by insulin secreted endogenously. In hypertensive subjects, however, this regulatory mechanism of the diuretic factors, such as insulin, EDLS and dopamine, is thought to be deranged, which might result in decompensation of a diuretic and antidiuretic balance leading to blood pressure elevation.

Adult↗

PubMed1995

Diagnostic significance of dopamine estimation using plasma and urine in patients with adrenal and renal insufficiency, renal transplantation and hypertension.

Although free and conjugated dopamine (DA) constitute most of the plasma and urine catecholamine pool, the diagnostic significance of DA estimation for the evaluation of illness is not clear. We evaluated the clinical utility of DA estimation by measuring free and conjugated DA in patients with various illness. Patients with adrenal insufficiency did not show decreases in DA concentrations but did demonstrate reductions in free and conjugated plasma adrenaline (Ad). Patients with established stage of essential hypertension exhibited decreased plasma concentrations of free and conjugated DA, although they were hyperadrenergic. In patients with chronic renal insufficiency and failure, the free DA concentration in the urine decreased depending on the severity of renal impairment. Conversely, plasma concentrations of conjugated DA are higher in patients with chronic renal failure than in normal subjects. The high plasma concentrations of conjugated DA decreased dramatically following hemodialysis and renal transplantation. Urinary free DA excretion increased markedly following renal transplantation. In conclusion, the estimation of the free and conjugated DA in plasma and urine is clinically useful for the diagnosis of adrenal insufficiency, essential hypertension, and renal insufficiency and failure. It also can be used to monitor the effectiveness of hemodialysis and renal transplantation.

Adrenal Insufficiency↗

PubMed1994

Modulation of sodium current by lactate in guinea pig ventricular myocytes.

OBJECTIVE: The aim was to elucidate whether or not lactate modifies the fast sodium current (INa) in cardiac cells. METHODS: A tight seal whole cell clamp technique was used to record the action potentials and INa in single ventricular cells from the guinea pig heart. RESULTS: In voltage clamp experiments, superfusion with 20 mM lactate shifted both the normalised conductance (gNa)-voltage relationship and the channel availability curve toward hyperpolarisation by approximately 4 mV, but did not affect the maximum conductance (gNa,max). In the test solution containing only CaCl2 as the main divalent component, 20 mM lactate reduced the ionised calcium concentration from 1.02 to 0.84 mM. When the calcium concentration was kept constant by the addition of CaCl2 into the lactate containing solution the lactate effect was nullified. However, a change in the calcium concentration from 1.0 to 0.84 mM without lactate induced a 4 mV negative shift of the channel availability curve. Current clamp experiments in Tyrode solution showed that 20 mM lactate shifted the threshold for the action potential upstroke by 2.5-3 mV, in accordance with the voltage clamp experiments. CONCLUSIONS: Lactate modifies INa of ventricular myocytes by shifting its kinetics toward hyperpolarisation. This shift seems to be caused exclusively by a decrease in the ionised divalent cation concentrations and a resultant change in the negative surface charge of the sarcolemma.

Action Potentials↗

PubMed1994

Relaxin increases heart rate by modulating calcium current in cardiac pacemaker cells.

Relaxin (RLX), a reproductive hormone of the insulin family, increases heart rate in experimental animals. The cellular and ionic mechanisms responsible for this positive chronotropic effect remain unknown. We have investigated the actions of RLX on the action potential and underlying transmembrane ionic currents in single sinoatrial node cells of the rabbit heart under whole-cell voltage-clamp conditions, using both nystatin-perforated-patch and membrane-ruptured techniques. In this preparation RLX (0.8 to 80 nmol/L) caused reversible increases in the rate of spontaneous action potentials and a dose-dependent increase in the L-type calcium current, ICa(L). The best-fit Langmuir relation for the augmentation of ICa(L) yielded a threshold concentration of 1 nmol/L and a KD of 14 nmol/L. These effects of RLX appear to be mediated by increases in intracellular cyclic AMP (cAMP), since RLX was without effect after application of (1) the beta-adrenergic agonist isoprenaline (1 mumol/L) or (2) superfusion of the intracellular second messenger cAMP (100 mumol/L) or 8-Br-cAMP (100 to 200 mumol/L). Internal dialysis with an inhibitor of cAMP-dependent protein kinase (PKI, 7 mumol/L) abolished the effects of RLX. These results provide the first electrophysiological evidence that RLX modulates heart rate and contractility by increasing ICa(L) and suggest that the biochemical mechanism involves the formation of cAMP and activation of cAMP-dependent protein kinase.

Action Potentials↗

PubMed1992

Blockade of Na+ current by promethazine in guinea-pig ventricular myocytes.

1. To elucidate the antiarrhythmic mechanism of promethazine, its effects on the fast Na+ current (INa) were examined in single guinea-pig ventricular myocytes by whole-cell voltage clamp methods. 2. Promethazine blocked INa with a KD of 42.6 microM and Hill's coefficient of 1.1 at a holding potential of -140 mV. 3. The INa blockade was enhanced at a less negative holding potential of -80 mV with a change of KD to 4.4 microM. Although 10 microM promethazine did not change the inactivation time constants of INa, it shifted the steady-state inactivation curve (h infinity curve) toward more negative potentials by 19.5 mV with the slope factor unaffected. 4. Double pulse experiments revealed that the development of blockade followed two-exponential functions having time constants of 7 and 220 ms at -20 mV. 5. Promethazine slowed the repriming of INa. This was associated with the development of slow phase having a time constant of 1160 +/- 59 ms. 6. Promethazine produced a profound use-dependent block when the cell was repeatedly stimulated with interpulse intervals shorter than 1 s. However, short pulses of 2 ms duration hardly produced such a use-dependent block. Hence, open channel blockade is considered to play a minor role in the promethazine action on INa. 7. These results suggest that promethazine blocks cardiac INa in a manner similar to class I antiarrhythmic drugs and that this effect may account for its antiarrhythmic action.

Algorithms↗

PubMed1992

Endothelin enhances delayed potassium current via phospholipase C in guinea pig ventricular myocytes.

The effects of endothelin, a novel vasoconstrictive peptide, on the delayed rectifier K+ current (IK) were examined in single dialyzed cells from guinea pig ventricles. Either big endothelin or endothelin-1 enhanced IK at a dissociation constant of 2 nM with L-type Ca2+ current being unaffected. Under intracellular perfusion with pCa 7.6 solution, 3 nM big endothelin increased IK by 55 +/- 38.5%. Either pretreatment with 10 microM 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H 7) or a low Ca2+ [10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and minus CaCl2] internal solution diminished the enhancement. Preceding stimulation of protein kinase C (PKC) by 10-20 nM 12-O-tetradecanoylphorbol-13-acetate also reduced the degree of enhancement. When Na+ was eliminated from the solutions, endothelin increased IK distinctively in cells internally dialyzed with a low Ca2+ solution. This enhancement was not abolished by either pretreatment with H 7 or by removal of Ca2+ from the external perfusate but by increasing the internal EGTA concentration to 40 mM. Preincubation with ryanodine or internal perfusion with heparin also reduced the IK enhancement under Na(+)-free conditions. Intracellular application of 200 microM guanosine 5'-O-(3-thiotriphosphate) effectively attenuated the effect of endothelin. It is concluded that endothelin enhances IK via phospholipase C-mediated PKC activation and intracellular Ca2+ mobilization. GTP-binding protein is involved in these reactions.

Animals↗

PubMed1991

Modulation of the delayed K+ current by histamine in guinea pig ventricular myocytes.

The effects of histamine on delayed K+ current (IK) were investigated in patch-clamped single guinea pig ventricular myocytes. Histamine increased IK with a maximal fractional response of 2.7 and a kd of 9.4 x 10(-7) mol/l. At a concentration of 10(-8) mol/l, histamine did not increase IK significantly, but increased ICa by 52% +/- 12%. The voltage-dependence of IK activation, the reversal potential and the time course of the IK tail decay were not changed by histamine. Under pretreatment with 10(-4) mol/l of ranitidine, neither histamine (10(-6) mol/l) nor 2-pyridylethylamine (10(-4) mol/l) caused any sizable increase in IK. When the cell was pretreated with a saturating dose of isoproterenol (10(-6) mol/l), histamine did not additively enhance IK. The IK enhancement by 3 x 10(-7) mol/l histamine was partially antagonized by concurrent exposure to 5 x 10(-6) mol/l carbachol. Whereas, use of a higher concentration of histamine (10(-6) mol/l) obscured the inhibitory effect of carbachol. It is concluded that histaminergic action of IK is attributed exclusively to H2 receptor-mediated reactions involving GS protein and adenylate cyclase.

Action Potentials↗

PubMed1991

Analysis of bites on three-dimensional vectorcardiography after coronary artery ligation in dogs.

The serial changes in the QRS loops of vectorcardiograms were investigated following ligation of a branch of the left anterior descending artery (LAD) by the three-dimensional rotation method in 18 dogs. Concave inflections of the QRS loop, defined as "bites," were best delineated when the loop was viewed from a left cranial or right caudal direction. Bites appeared 48 +/- 8 minutes after LAD ligation in all of the dogs, and their development was closely related to the temporal changes in the % sigma R and QRS point score on a standard 12-lead electrocardiogram. Q waves were not observed on the electrocardiograms in 9 dogs. In the remaining 9, they appeared 117 +/- 18 minutes after LAD ligation. The bite duration, area, and amplitude were compared with the anatomical extent of the infarcts. A significant positive correlation was found between bite duration and infarct size. The detection of bites on the three-dimensionally rotated vectorcardiogram appears to have a high sensitivity for anterior myocardial infarction and could potentially become a useful diagnostic tool.

Animals↗

PubMed1991

Effects of intracerebroventricular and intravenous injections of endothelin-1 on blood pressure and sympathetic activity in urethane-anesthetized rats.

Because endothelin-1 (ET-1) is believed to be an endogenous calcium-channel agonist, it was thought that it may affect not only vascular smooth muscle cells but also nerve activity. Intravenous injections of ET-1 (0.01 nmol) did not affect cardiovascular parameters or renal sympathetic activity. ET-1 (1 nmol) initially decreased blood pressure for a few minutes, and then caused an increase for 5-10 min. Blood pressure then returned to baseline but later there was a rise in pressure for more than 60 min. Sympathetic activity was markedly suppressed during the initial hypertensive phase but increased during the later phase. Intracerebroventricular injections of ET-1 increased blood pressure even with the small dose (0.01 nmol). The increase was maintained for about 10 min, and returned to baseline. It then decreased abruptly with marked bradycardia, and finally returned to the baseline 60-90 min later. These results indicate that ET-1 affects not only the vascular smooth muscle but also the autonomic nervous system to influence cardiovascular functions.

Anesthesia↗

PubMed1991

Caffeine-induced block of Na+ current in guinea pig single ventricular cells.

Effects of caffeine on Na+ current (INa) were investigated in single ventricular cells from guinea pigs using the whole cell clamp method. With a Ca(2+)-containing internal solution (pCa 8.2), 10 mM caffeine blocked INa by 17.5 +/- 4.6% at a -120-mV holding potential. It was accompanied by 3- to 5-mV shifts of the steady-state inactivation curve and time constant-voltage relationship toward hyperpolarization. The inactivation kinetics spontaneously shifted toward hyperpolarization at 0.30 +/- 0.17 mV/min. The spontaneous shift was accompanied by a similar negative shift of the threshold potential, whereas caffeine did not affect it. Caffeine retarded the recovery of INa from inactivation, and a 4-mV positive shift in the recovery potential produced a similar retardation in INa recovery without caffeine. The INa block by caffeine was not influenced by reinforcing the internal buffering capacities using internal solutions containing 40 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid or 50 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid or by pretreating the cell with 1 microM ryanodine. Neither pretreatment with isoproterenol or H 7 nor prestimulation of Gs protein by nonhydrolyzable GTP (GTP gamma S) altered the effects of caffeine on INa. It is concluded that caffeine inhibits INa and shifts the inactivation kinetics without being mediated by changes in intracellular ionic composition or intracellular signaling systems. Direct action on the channel proteins may be involved.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗