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Biomedical subjects

A Mugelli

Publications and source records attributed to A Mugelli.

At least 19 recordsLinked to original sources
PubMed2001

The properties of the pacemaker current I(F)in human ventricular myocytes are modulated by cardiac disease.

The pacemaker current I(f)is present in ventricular myocytes from the human failing heart where it may contribute to arrhythmogenesis. The role of cardiac disease in the modulation of I(f)expression is still uncertain. We studied the functional expression and properties of I(f)in human ventricular myocytes isolated from control donor hearts or from explanted failing hearts of patients with ischemic and dilated cardiomyopathy. In patch-clamped cells, I(f)was elicited by hyperpolarization. Membrane capacitance (C(m)) was significantly higher in dilated cardiomyopathy than in control or ischemic cardiomyopathy. I(f)was present in all ischemic and dilated cardiomyopathy tested cells and in 76% of control cells. In ischemic and dilated cardiomyopathy, I(f)amplitude measured at -120 mV was significantly greater than in control. However, I(f)density (i.e. current normalized to C(m)) was significantly higher in ischemic cardiomyopathy (2.0+/-0.2 pA/pF) than in dilated cardiomyopathy (1.2+/-0.1 pA/pF) or control (1.0+/-0.1 pA/pF). In diseased hearts, the activation curve was significantly shifted to more positive values compared to control. The slope of the fully-activated I-V relations was greater in ischemic cardiomyopathy than in dilated cardiomyopathy or control (P<0.05) while the intercept with the x -axis (V(rev)) was similar. In conclusion, I(f)is overexpressed in human ventricular myocytes from failing hearts; its functional expression seems related to the etiology of the disease, being higher in ischemic than in dilated cardiomyopathy, and not to the degree of cell hypertrophy.

Adult↗
PubMed2001

Myocardial remodeling and arrhythmogenesis in moderate cardiac hypertrophy in rats.

In 47 male adult Wistar rats with 4-wk aortic coarctation (AC) and 39 age-matched sham-operated rats (SO) chronically instrumented for telemetry electrocardiogram recording, we investigated the mechanisms of arrhythmogenesis in moderate cardiac hypertrophy, with an approach from "in vivo" toward the cellular level, analyzing 1) stress-induced cardiac arrhythmias in all rats and 2) myocardial fibrosis in 35 animals and action potential duration and density of hyperpolarization-activated current in 19 others at the ventricular level. Aortic banding increased arterial blood pressure, cardiac weight, and ventricular myocyte volume by 11, 25, and 14%, respectively (P < 0.001-0.05). Ventricular arrhythmias occurred at similar rates in AC and SO rats throughout the stress procedure. Action potential duration and hyperpolarization-activated current were about twice as great and myocardial fibrosis about four times greater in AC animals (P < 0.005-0.05). Electrocardiogram data also revealed more supraventricular arrhythmias in AC rats during the baseline period and after stress and fewer atrioventricular block episodes after stress (P < 0.05). Thus stress-induced supraventricular and atrioventricular nodal, but not ventricular, arrhythmias were affected in moderate cardiac hypertrophy when ventricular morphofunctional alterations were evident.

Action Potentials↗
PubMed2000

Long-term treatment of spontaneously hypertensive rats with losartan and electrophysiological remodeling of cardiac myocytes.

OBJECTIVE: Cardiac hypertrophy due to pressure overload is associated with several cellular electrophysiological alterations such as prolongation of action potential duration (APD), decrease in transient outward current (Ito) and occurrence of the pacemaker current I(f). These alterations may play a role in sudden arrhythmic death, which is a major risk factor in myocardial hypertrophy and failure. Since angiotensin II is a key signal for myocyte hypertrophy, we tested if an 8-week treatment of old spontaneously hypertensive rats (SHR) with the antagonist of type-1 angiotensin II receptor (AT1), losartan (10 mg/kg/day), was able to influence the cellular electrophysiologic remodeling associated with cardiac hypertrophy. METHODS: Left ventricular myocytes were isolated from control (CTR) or losartan-treated (LOS) 18-month old SHR. Patch-clamped LVM were superfused with a normal Tyrode's solution (to measure action potential) or appropriately modified Tyrode's solution (to measure Ito and I(f)). RESULTS: Heart weight to body weight ratio (HW/BW) was significantly smaller in LOS (5.69 +/- 0.25 mg/g) than in CTR rats (6.67 +/- 0.37 mg/g; P < 0.05). Membrane capacitance, an index of cell size, was significantly reduced in LOS (342 +/- 12, n = 92) vs. CTR (422 +/- 14 pF, n = 96, P < 0.001). APD was significantly shorter in LOS than in CTR (at -60 mV: 197 +/- 23 vs. 277 +/- 19 ms, n = 28, P < 0.001); this effect was paralleled by a larger maximum Ito density in the LOS group (LOS: 15.1 +/- 1.4 pA/pF, CTR: 10.0 +/- 0.8 pA/pF) (n = 27, P < 0.02). I(f), elicited by hyperpolarizing steps (range: -60 to -130 mV), was consistently recorded in SHR cells; however, its maximal specific conductance was significantly lower in LOS than in CTR rats (28.6 +/- 3.6 vs. 54.2 +/- 8.0 pS/pF, n = 55, P < 0.001). Voltage of half-maximal activation (V1/2) of both Ito and I(f) was unchanged by the treatment. CONCLUSIONS: AT1 receptor blockade with losartan prevents the development of myocyte hypertrophy and associated electrophysiological alterations in old SHR.

Action Potentials↗
PubMed2000

Use of antihypertensive drugs in the Italian hospitals. GIFA group. Gruppo Italiano di Farmacoepidemiologia nell'Anziano.

Calcium channel blockers and ACE-inhibitors are among the most common drugs prescribed for the initial treatment of hypertension. While their ability to control surrogate outcomes, such as blood pressure and left ventricular hypertrophy, is proven, there is limited evidence of their prevention of major cardiovascular events, including mortality. The aim of our work was to assess the use of these drugs in Italy in comparison with beta-blockers and diuretics. We examined the consumption of the four main antihypertensive classes of drugs (beta-blockers, diuretics, calcium channel blockers and ACE- inhibitors). In-hospitalization data from the GIFA (Gruppo Italiano di Farmacoepidemiologia nell'Anziano) database were used. During the period from 1988 to 1995, the most frequently prescribed antihypertensive drugs were calcium channel blockers (47%) followed by diuretics (37%), ACE-inhibitors (33%) and beta-blockers (5.5%). Changes over time in the use of these drugs were analysed: ACE-inhibitors had the greatest increase in use over time. Calcium channel blockers, ACE-inhibitors and beta-blockers were usually prescribed to the youngest patients (aged <65 years), while diuretics to the oldest. Calcium channel blockers were prescribed to 60% of patients with myocardial infarction and to 55% of those with congestive heart failure. In conclusion, our study demonstrates that the Italian physicians very often prescribe drugs like calcium channel blockers and ACE-inhibitors. Among these pharmacological agents, enalapril (twice per day) and slow release calcium channel blockers are the most frequently prescribed drugs.

Adrenergic beta-Antagonists↗
PubMed2000

Isolated cardiac cells for electropharmacological studies.

Single cardiac myocytes provide a model widely used to characterize the electrophysiological properties of drugs and to identify new therapeutic targets. This review focuses on isolation procedures to obtain single cardiac myocytes from several mammal species, including humans, and on patch-clamp technique as a useful method to investigate the molecular mechanism of druy actions.

Animals↗
PubMed2000

Electrophysiologic effects of lercanidipine on repolarizing potassium currents.

Blockade of cardiac repolarizing potassium channels by drugs may result in QT-interval prolongation, eventually degenerating into "torsades de pointes," a life-threatening arrhythmia. Lercanidipine (LER) is a recently introduced lipophilic calcium antagonist with no cardiodepressant activity and long-lasting antihypertensive action. Its chemical structure is characterized by the presence of a diphenylpropylaminoalkyl group, which is present in some of the drugs that have been reported to cause QT-interval prolongation. Our previous data demonstrated that LER blocks L-type calcium channels without affecting sodium current; however, no data are available concerning its effects on cardiac potassium channels. Transient outward (I(to)), delayed rectifier (I(K)), background currents, and action potential (AP) profile were measured from patch-clamped ventricular myocytes isolated from rat, guinea pig, or human hearts using enzymatic dissociation procedures. LER did not affect I(K) (and I(Kr)) density and activation curve in guinea pig myocytes; the reversal potential of the background current (I(K1)) and its slope were not changed by the drug. Maximal diastolic potential (MDP) and duration of the AP measured at -60 mV (APD(-60)) were not significantly changed. I(to) density and activation curves measured in rat myocytes were similar in the absence and presence of 1 or 10 microM LER. Finally, the effect of LER was tested in human ventricular myocytes: superfusion with 1 microM LER did not affect MDP and APD(-60). I(to) density and the midpoint of activation and inactivation curves were similar in the absence and presence of LER. In conclusion, our data demonstrate that LER does not affect repolarizing potassium currents and action potential profile recorded from guinea pig, rat, and human ventricular myocytes. It is unlikely that LER could cause QT prolongation in vivo.

Action Potentials↗
PubMed1999

Modulation of the pacemaker current If by beta-adrenoceptor subtypes in ventricular myocytes isolated from hypertensive and normotensive rats.

OBJECTIVE: Both beta 1- and beta 2-adrenoceptors (beta 1-AR and beta 2-AR) are functionally present in human and rat ventricular myocytes. The two receptor subtypes are differently regulated during the development of myocardial hypertrophy and failure. I(f) is expressed in human and rat ventricular myocytes. In hypertrophied myocytes isolated from old spontaneously hypertensive rats (SHR) the density is much larger than in age-matched normotensive Wistar Kyoto (WKY). Due to the possible relevance of I(f) as an arrhythmogenic mechanism in the rat and human ventricle, we studied and compared the effects of beta 1-AR and beta 2-AR stimulation on I(f) in both hypertrophied and normal left ventricular myocytes of 18-month old SHR and WKY. METHODS: The whole-cell configuration of the patch-clamp technique was employed. Noradrenaline (NA, 1 microM) was used to stimulate beta 1-AR and isoprenaline (ISO, 1 microM) in the presence of the beta 1-AR antagonist CGP 20712A (0.1 microM) to stimulate beta 2-AR. RESULTS: In SHR, NA increased I(f) by causing a 10.8 +/- 0.9 mV (n = 10) positive shift in the voltage of maximal activation (V1/2); this effect was completely reversed by CGP 20712A. beta 2-AR stimulation was effective in seven out of 13 cells tested, where it caused a small positive shift in V1/2 (4.0 +/- 1.7 mV). Cyclopentyladenosine (CPA), a selective A1-receptor agonist, reversed the effect of NA; the antiadrenergic action of CPA was abolished in cells pre-incubated with pertussis toxin (PTX) to block inhibitory G proteins (Gi). In PTX-treated cells the shift in V1/2 caused by both beta 2-AR (9.6 +/- 1.7 mV, n = 6, p < 0.05) and beta 1-AR (17.6 +/- 1.9 mV, n =7, p < 0.05) was significantly greater than in control cells. Both beta-AR subtypes modulated I(f) activation also in WKY: beta 1-AR shifted V1/2 by 16.0 +/- 1.4 mV (n = 15) and beta 2-AR by 4.2 +/- 1.1 mV (n = 7). However, in PTX-treated WKY cells only the beta 2-AR effect was potentiated (shift in V1/2: 11.4 +/- 1.4 mV, n = 9, p < 0.01), while the beta 1-AR response was unchanged (18.9 +/- 4.2 mV, n = 5, n.s.). CONCLUSIONS: I(f) expressed in SHR hypertrophied ventricular myocytes is modulated by catecholamines mainly through the stimulation of the beta 1-AR subtype. The beta 1-AR response is, however, significantly lower than that observed in myocytes from normotensive rats, probably as a consequence of the presence of an increased inhibitory activity of Gi proteins. This post-receptorial control may be seen as a mechanism to limit the arrhythmogenicity of beta-AR stimulation in myocardial hypertrophy and failure.

Action Potentials↗
PubMed1999

Influence of postnatal-development on I(f) occurrence and properties in neonatal rat ventricular myocytes.

OBJECTIVE: I(f) is a hyperpolarization-activated current, which plays a key role in determining the spontaneous rate of cardiac pacemaker cells. We have previously shown that I(f) is also expressed in left ventricular myocytes isolated from spontaneously hypertensive rats; in these cells, its occurrence and density is linearly related with the severity of myocardial hypertrophy. Since hypertrophy induces a re-expression of genes encoding fetal proteins, we investigated changes in I(f) properties during post-natal development. METHODS: Fresh ventricular myocytes were enzymatically isolated from the heart of 1-2- to 28-day-old Wistar rats. The whole-cell configuration of the patch-clamp technique was employed to record the action potential and I(f). RESULTS: Membrane capacitance, an index of cell size, progressively increased from 13 +/- 1 pF at 1-2 days to 66 +/- 4 pF at 28 days of age (p < 0.01). At 1-2 days, a cesium-sensitive hyperpolarization-activated inward current (I(f)) was recorded in the majority of tested cells (n = 51). The midpoint of the activation curve (V1/2) was -78 +/- 2 mV (n = 32), and specific current conductance of fully activated I(f) (gf.max) was 60 +/- 11 pS/pF. Reversal potential (Vrev) measured by tail-current analysis was -24 +/- 3 mV (n = 8). Reduction of extracellular Na+ from 140 to 35 mM or extracellular K+ from 25 to 5.4 mM caused a shift of -12 +/- 1 mV (n = 3) or -11 +/- 2 mV (n = 5) of Vrev, respectively. Occurrence of I(f) decreased with aging, being present in 64%, 48% and 32% of cells at 10, 15 and 28 days, respectively. When present, I(f) density was significantly smaller than at 1-2 days (p < 0.05), reaching a value of 8 +/- 2 pS/pF at 28 days. However, V1/2 did not change in the older rats, being -80 +/- 2, -83 +/- 4 and -85 +/- 3 mV at 10, 15 and 28 days, respectively. Vrev at 10 and 15 days was -27 and -28 mV, respectively, thus suggesting that channel selectivity did not change. CONCLUSIONS: The pacemaker current, I(f), is expressed in ventricular myocytes from neonatal rats and progressively disappears; when present, it shows electrophysiological properties similar to I(f) re-expressed in hypertrophied adult rat ventricular myocytes. Thus, it is likely that the occurrence of I(f) in ventricular myocytes of hypertrophied and failing hearts is due to the re-expression of a fetal gene.

Action Potentials↗
PubMed1998

Effect of 5-HT4 receptor stimulation on the pacemaker current I(f) in human isolated atrial myocytes.

OBJECTIVE: 5-HT4 receptors are present in human atrial cells and their stimulation has been implicated in the genesis of atrial arrhythmias including atrial fibrillation. An I(f)-like current has been recorded in human atrial myocytes, where it is modulated by beta-adrenergic stimulation. In the present study, we investigated the effect of serotonin (5-hydroxytryptamine, 5-HT) on I(f) electrophysiological properties, in order to get an insight into the possible contribution of I(f) to the arrhythmogenic action of 5-HT in human atria. METHODS: Human atrial myocytes were isolated by enzymatic digestion from samples of atrial appendage of patients undergoing coeffective cardiac surgery. Patch-clamped cells were superfused with a modified Tyrode's solution in order to amplify I(f) and reduce overlapping currents. RESULTS AND CONCLUSIONS: A time-dependent, cesium-sensitive increasing inward current, that we had previously described having the electrophysiological properties of the pacemaker current I(f), was elicited by negative steps (-60 to -130 mV) from a holding potential of -40 mV. Boltzmann fit of control activation curves gave a midpoint (V1/2) of -88.9 +/- 2.6 mV (n = 14). 5-HT (1 microM) consistently caused a positive shift of V1/2 of 11.0 +/- 2.0 mV (n = 8, p < 0.001) of the activation curve toward less negative potentials, thus increasing the amount of current activated by clamp steps near the physiological maximum diastolic potential of these cells. The effect was dose-dependent, the EC50 being 0.14 microM. Maximum current amplitude was not changed by 5-HT. 5-HT did not increase I(f) amplitude when the current was maximally activated by cAMP perfused into the cell. The selective 5-HT4 antagonists, DAU 6285 (10 microM) and GR 125487 (1 microM), completely prevented the effect of 5-HT on I(f). The shift of V1/2 caused by 1 microM 5-HT in the presence of DAU 6285 or GR 125487 was 0.3 +/- 1 mV (n = 6) and 1.0 +/- 0.6 mV (n = 5), respectively (p < 0.01 versus 5-HT alone). The effect of 5-HT4 receptor blockade was specific, since neither DAU 6285 nor GR 125487 prevented the effect of 1 microM isoprenaline on I(f). Thus, 5-HT4 stimulation increases I(f) in human atrial myocytes; this effect may contribute to the arrhythmogenic action of 5-HT in human atrium.

Action Potentials↗
PubMed1998

Effect of some cyclooxygenase inhibitors on the increase in guanosine 3':5'-cyclic monophosphate induced by NO-donors in human whole platelets.

1. The effect of the NSAIDs indomethacin, indoprofen, diclofenac and acetylsalicylic acid on the increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) induced by nitric oxide-donor agents was tested in human whole platelets and in platelet crude homogenate. 2. In whole platelets, indomethacin reduced the increase in cyclic GMP induced by the nitric oxide-donors (NO-donors) sodium nitroprusside (NaNP) and S-nitroso-N-acetylpenicillamine (SNAP) in a dose-dependent way, its IC50 being 13.7 microM and 15.8 microM, respectively. 3. Of the other cyclooxygenase inhibitors tested, only indoprofen reduced the increase in cyclic GMP induced by both NO-donors in a dose-dependent way (IC50=32.7 microM, NaNP and 25.0 microM, SNAP), while acetylsalicylic acid (up to 1000 microM) and diclofenac (up to 100 microM) were ineffective. 4. However, in platelet crude homogenate neither indomethacin nor indoprofen reduced the cyclic GMP production. 5. Indomethacin (10 microM), indoprofen (30 microM), diclofenac (100 microM) and acetylsalicylic acid (1000 microM) showed a comparable efficacy in inhibiting platelet thromboxane B2 (TXB2) production, suggesting that the inhibitory effect of indomethacin and indoprofen on the increase in cyclic GMP induced by both NO-donors was not mediated by inhibition of cyclooxygenase. 6. In vitro, the NSAIDs analysed did not interfere with nitrite production of SNAP. 7. The unhomogeneous behaviour of NSAIDs on the increase in cyclic GMP induced by NO-donors in whole platelets may contribute to the different pharmacological and toxicological characteristics of the drugs, providing new knowledge on the effect of indomethacin and indoprofen.

Acetophenones↗
PubMed1997

Characterization of the hyperpolarization-activated current, I(f), in ventricular myocytes from human failing heart.

BACKGROUND: Disease-associated electrophysiological alterations may contribute to the increased predisposition to arrhythmias of the hypertrophied or failing myocardium. An I(f)-like current is expressed in rat left ventricular myocytes (LVMs), its amplitude being linearly related to the severity of cardiac hypertrophy. Here, we report the occurrence and electrophysiological properties of I(f) in human LVMs. METHODS AND RESULTS: LVMs were isolated from hearts of three male patients undergoing cardiac transplantation for terminal heart failure due to ischemic dilated cardiomyopathy. The patch-clamp technique was used to record I(f), ie, a barium-insensitive, cesium-sensitive, time-dependent increasing inward current elicited on hyperpolarization. Membrane capacitance was 244 +/- 27 pF (n = 25). I(f) occurred in all cells tested; its density measured at -120 mV was 2.1 +/- 0.3 pA/pF. Activation curves of I(f) (n = 24) were fitted by a Boltzmann function; the threshold was -55 mV; midpoint, -70.9 +/- 2.1 mV; slope, -5.4 +/- 0.3 mV; and maximal specific conductance, 19.6 +/- 2.5 pS/pF. I(f) blockade by extracellular cesium was voltage dependent. Reducing extracellular potassium concentration from 25 to 5.4 mmol/L caused a shift of the reversal potential from -12.7 +/- 0.5 to -24.8 +/- 2.1 mV and a 64% decrease of current conductance. CONCLUSIONS: I(f) is present in human LVMs. Its electrophysiological characteristics resemble those previously described in hypertrophied rat LVMs and suggest that I(f) could be an arrhythmogenic mechanism in patients with severe heart failure.

Cardiac Output, Low↗
PubMed1997

Characteristics of L-type calcium channel blockade by lacidipine in guinea-pig ventricular myocytes.

1. The Ca(2+)-antagonistic properties of lacidipine were investigated in patch-clamp guinea-pig ventricular myocytes. 2. In basal conditions, 0.1 microM lacidipine reduced the action potential duration, associated with a decrease in the L-type calcium current (ICa,L) to 66 +/- 4% of the control value, without a change in the current-voltage relationship. Sodium current and background potassium currents were not affected. All the effects reached a steady state within 2 min. 3. The Ca(2+)-antagonistic effect of lacidipine was voltage-dependent: a marked negative shift (about 20 mV) of the steady-state inactivation curve was observed with long (10 s) conditioning prepulses, but not with short (350 ms) prepulses. 4. The onset of and recovery from the voltage-dependent effect caused by 0.1 microM lacidipine were significantly slower when compared to those of equiactive concentrations of nimodipine (0.5 microM) and nisoldipine (0.1 microM). ICa,L measured after prepulses at -40 mV lasting 500 ms or less was unchanged (95 +/- 5% of maximum current value) while it was reduced to 49 +/- 10% by nimodipine and 43 +/- 9% by nisoldipine (P < 0.05 vs lacidipine for both). 5. Similarly, the recovery from block in the presence of lacidipine was slower than with nimodipine and nisoldipine. After a prepulse of 1 s at -80 mV, ICa,L recovered up to 54 +/- 2% of the maximum current value in the presence of lacidipine, and up to 91 +/- 3% and 93 +/- 5% in the presence of nimodipine and nisoldipine, respectively (P < 0.05 vs lacidipine). 6. Blockade of ICa,L by lacidipine was use-dependent. After ten 200 ms long pulses (1 Hz) from -80 mV, ICa,L was reduced to 55 +/- 7% of the current measured at the first pulse. In the presence of nimodipine and nisoldipine, ICa,L elicited by the tenth pulse amounted to 93 +/- 3% and 80 +/- 6% of the first pulse value, respectively (P < 0.05 vs lacidipine). Lacidipine did not cause use-dependent blockade of ICa,L in cells stimulated with 10 ms long pulses. 7. These results demonstrate that lacidipine selectively inhibits ICa,L in isolated cardiomyocytes and suggest that this effect occurs mainly through binding to the inactivated Ca2+ channels.

Animals↗
PubMed1997

The pacemaker current I(f) in single human atrial myocytes and the effect of beta-adrenoceptor and A1-adenosine receptor stimulation.

1. We used single human atrial myocytes to study I(f) occurrence, properties and pharmacological modulation. Cells were obtained by chunk enzymatic digestion from samples of right atrial appendages of patients undergoing corrective cardiac surgery. 2. Patch-clamped cells in the whole-cell configuration were superfused with a modified Tyrode solution to reduce contamination by interfering currents and to amplify I(f). The average cell membrane capacitance was 85.06+/-2.41 pF (n=531). Data were consistent with the geometrical dimensions of the cells (length 94.2+/-1.89 microm, width 17.9+/-0.42 microm, n=126). 3. When hyperpolarizing to -120 mV from a holding potential of -40 mV, 252 of 306 tested cells (82%) expressed a hyperpolarization-activated inward current (I(f) density=3.77+/-0.25 pA pF(-1)); the current was considered to be present in a given cell if its density at -120 mV was larger than 0.5 pA pF(-1). 4. Current activation was sigmoidal and fitted a Boltzmann model; the average activation curve (n=25) showed a maximum current amplitude of 205.97+/-19.94 pA, corresponding to 3.87+/-0.63 pA pF(-1), voltage of half-maximal activation (V(1/2)) at -86.68+/-2.19 mV and a slope of -11.39+/-0.69 mV. The reversal potential of I(f) measured by tail-current analysis was -13.07+/-1.92 mV (n=6). The addition of CsCl (5 mM) fully and reversibly blocked the current. 5. In the presence of the beta-adrenoceptor agonist isoprenaline (Iso, 1 microM), V(1/2) was significantly shifted toward less negative potentials by 6.06+/-1.96 mV (n=16, P=0.0039). The selective A1-adenosine receptor agonist cyclopentyladenosine (CPA, 1 microM) caused a statistically significant shift of V(1/2) toward more negative potentials with respect to the control curve, both in the absence (-7.37+/-1.83 mV, P=0.0005, n=11) and in the presence of 1 microM Iso (-4.97+/-1.78, P=0.031, n=6). 6. These results demonstrate that a current with the properties of I(f) described in cardiac primary and secondary pacemakers occurs in the majority of human atrial cells. While the pathophysiological relevance of I(f) in human atrial tissue remains to be defined, our data clearly show that it is modulated through stimulation of beta-adrenoceptors and A1-adenosine receptors.

Adenosine↗
PubMed1997

Protective effect of darodipine, a calcium antagonist, on rat cardiomyocytes against oxygen radical-mediated injury.

1. We used electrophysiological and electron spin resonance (e.s.r.) techniques to study the mechanism of the protective effect of darodipine on rat isolated cardiomyocytes exposed to an exogenous source of oxygen free radicals (OFR). 2. The L-type calcium current (I(Ca,L)), action potential and cell shortening were measured in patch-clamped cells in the whole-cell configuration. I(Ca,L) blockade by darodipine was concentration-dependent, peak current being reduced by 20% with 50 nM and by 58% with 100 nM darodipine. The lowest concentration of darodipine did not affect action potential or twitch profile. 3. Exposure to OFR-generating solution (5 mM dihydroxyfumarate, DHF) caused the appearance of electrophysiological alterations and/or spontaneous activity in 73% of cells (n=26) within 5 min; action potential duration (APD) was prolonged (195+/-16 ms vs 140+/-6 ms in the control) and maximum diastolic potential (MDP) was reduced (-59.5+/-2.6 mV vs -69.8+/-0.8 mV in the control) (P<0.05, n=25). 4. A 2 min pretreatment with 50 nM darodipine significantly reduced the incidence of these arrhythmogenic events following a 5 min exposure to OFR (36% of cells, n=14; P<0.05 vs nonpretreated cells). Pretreatment with darodipine also prevented APD prolongation caused by OFR (137+/-12 ms after DHF vs 117+/-6 ms before DHF n=14, not significant) but not the decrease of MDP (-63.4+/-2.5 mV after DHF vs -70.9+/-1.0 mV before DHF, P<0.05). 5. The e.s.r. spectra obtained from the DHF-DMPO solution in the absence of darodipine demonstrated the presence of two components corresponding to two DMPO adducts. The addition of darodipine (50-500 nM) led to a concentration-dependent decrease in intensity of the signals, the intensity of the DMPO-COO.- adduct being decreased more than that of the DMPO-OH. adduct. 6. Our results demonstrate that darodipine dose-depentently blocks I(Ca,L) in rat isolated cardiomyocytes. Furthermore it exerts protective effects against free-radical-induced electrophysiological alterations independently of its calcium antagonistic properties; this effect is possibly due to trapping of specific radical species.

Animals↗
PubMed1996

Calcium-dependent electrophysiological alterations in hypertrophied rat cardiomyocytes.

We compared the occurrence of calcium-dependent electrophysiological alterations in left ventricular myocytes isolated from the heart of old spontaneously hypertensive (SHR) and age-matched normotensive Wistar Kyoto rats (WKY). Electrical and mechanical activity were measured in patch-clamped myocytes in which intracellular Ca2+ was allowed to change freely. In parallel experiments, intracellular Ca2+ concentration was monitored in fura-2-AM preloaded cells using an image analysis system. Left ventricular myocytes from SHR showed a significantly greater membrane capacitance (an index of cell size), a prolonged duration of the action potential and a higher incidence of delayed afterdepolarization (DADs) and associated aftercontractions, and of spontaneous activity. DADs were likely generated by intracellular Ca2+ waves due to spontaneous and local Ca2+ release from intracellular stores. These results demonstrate that DADs, possibly related to spontaneous intracellular Ca2+ waves, occur frequently in hypertrophied rat cardiomyocytes and may be a relevant arrhythmogenic mechanism.

Animals↗