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Ronald Wilders

Publications and source records attributed to Ronald Wilders.

28 records · Page 2Linked to original sources
PubMed2004

NHE-1 and NBC during pseudo-ischemia/reperfusion in rabbit ventricular myocytes.

Despite many studies into the pathophysiology of cardiac ischemia-reperfusion injury, a number of key details are as yet undisclosed. These include the timing and magnitude of the changes in both Na(+)/H(+) exchange (NHE-1) and Na(+) -- HCO(3)(-) -cotransport (NBC) transport rates. We fluorimetrically measured H(i)(+) fluxes (J(NHE-1) and J(NBC)) and Na(i)(+) fluxes in single contracting rabbit ventricular myocytes subjected to metabolic inhibition, pseudo-ischemia (i.e. metabolic inhibition and extracellular acidosis of 6.4), and pseudo-reperfusion. Metabolic inhibition and pseudo-ischemia inhibited NHE-1 by 43 +/- 3.1% and 91 +/- 3.6%, and NBC by 66 +/- 5.4% and 100%, respectively. Inhibition was due to both an acidic shift of the pH(i) at which NHE-1 and NBC become quiescent (set-point pH(i)) and a reduction of the steepness of the pH(i) -- H(i)(+) flux profiles. NHE-1 and NBC did not contribute to Na(i)(+) loading during metabolic inhibition (Na(i)(+) 18 +/- 1.7 mM) or pseudo-ischemia (Na(i)(+) 21 +/- 1.7 mM), because pH(i) acidified less than set-point pH(i)'s. Upon pseudo-reperfusion NBC recovered to 54 +/- 7.3% but NHE-1 to 193 +/- 11% of aerobic control flux, and set-point pH(i)'s returned to near neutral values. Metabolic inhibition and reperfusion caused an acid load of 18 +/- 3.2 mM H(+) 94% of which were extruded by the hyperactive NHE-1. At pseudo-reperfusion Na(i)(+) rose sharply to 31 +/- 5.8 mM within 1.5 min and that coincided with hypercontracture. Cariporide not only prevented the Na(i)(+) transient, but also inhibited pH(i) recovery and prevented hypercontracture. Our results are consistent with the view that NHE-1 is active during metabolic inhibition if, like in whole hearts, pH(i) is driven more acidic than NHE-1 set-point pH(i). Furthermore, either an acidic pH(i) or absence of additional Na(i)(+) loading during reperfusion, or both, limit ischemia-reperfusion injury.

Animals↗
PubMed2003

Tidal volume, cardiac output and functional residual capacity determine end-tidal CO2 transient during standing up in humans.

In man assuming the upright position, end-tidal P(CO(2)) (P(ETCO(2))) decreases. With the rising interest in cerebral autoregulation during posture change, which is known to be affected by P(ETCO(2)), we sought to determine the factors leading to hypocapnia during standing up from the supine position. To study the contribution of an increase in tidal volume (V(T)) and breathing frequency, a decrease in stroke volume (SV), a ventilation-perfusion (V/Q) gradient and an increase in functional residual capacity (FRC) to hypocapnia in the standing position, we developed a mathematical model of the lung to follow breath-to-breath variations in P(ETCO(2)). A gravity-induced apical-to-basal V/Q gradient in the lung was modelled using nine lung segments. We tested the model using an eight-subject data set with measurements of V(T), pulmonary O(2) uptake and breath-to-breath lumped SV. On average, the P(ETCO(2)) decreased from 40 mmHg to 36 mmHg after 150 s standing. Results show that the model is able to track breath-to-breath P(ETCO(2)) variations (r(2)= 0.74, P P 0.05). Model parameter sensitivity analysis demonstrates that the decrease in P(ETCO(2)) during standing is due primarily to increased V(T), and transiently to decreased SV and increased FRC; a slight gravity-induced V/Q mismatch also contributes to the hypocapnia. The influence of cardiac output on hypocapnia in the standing position was verified in experiments on human subjects, where first breathing alone, and then breathing, FRC and V/Q were controlled.

Adult↗
PubMed2003

Conduction slowing by the gap junctional uncoupler carbenoxolone.

BACKGROUND: Cellular electrical coupling is essential for normal propagation of the cardiac action potential, whereas reduced electrical coupling is associated with arrhythmias. Known cellular uncoupling agents have severe side effects on membrane ionic currents. We investigated the effect of carbenoxolone on cellular electrical coupling, membrane ionic currents, and atrial and ventricular conduction. METHODS AND RESULTS: In isolated rabbit left ventricular and right atrial myocytes, carbenoxolone (50 micromol/l) had no effect on action potential characteristics. Calcium, potassium, and sodium currents remained unchanged. Dual current clamp experiments on poorly coupled cell pairs revealed a 21+/-3% decrease in coupling conductance by carbenoxolone (mean+/-S.E.M., n=4, p<0.05). High-density activation mapping was performed in intact rabbit atrium and ventricle during Langendorff perfusion of the heart. The amplitude of the Laplacian of the electrograms, a measure of coupling current in intact hearts, decreased from 1.45+/-0.66 to 0.75+/-0.51 microA/mm(3) (mean+/-SD, n=32, p<0.05) after 15 min of carbenoxolone. Carbenoxolone reversibly decreased longitudinal and transversal conduction velocity from 66+/-15 to 49+/-16 cm/s and from 50+/-14 to 35+/-15 cm/s in ventricle, respectively (mean+/-SD, n=5, both p<0.05). In atrium, longitudinal and transversal conduction velocity decreased from 80+/-29 to 60+/-16 cm/s and from 49+/-10 to 38+/-10 cm/s (mean+/-SD, n=8, both p<0.05). CONCLUSIONS: Carbenoxolone-induced uncoupling causes atrial and ventricular conduction slowing without affecting cardiac membrane currents. Activation delay is larger in poorly coupled cells.

Action Potentials↗
PubMed2003

Ionic remodeling of sinoatrial node cells by heart failure.

BACKGROUND: In animal models of heart failure (HF), heart rate decreases as the result of an increase in intrinsic cycle length of the sinoatrial node (SAN). In this study, we evaluate the HF-induced remodeling of membrane potentials and currents in SAN cells. METHODS AND RESULTS: SAN cells were isolated from control rabbits and rabbits with volume and pressure overload-induced HF and patch-clamped to measure their electrophysiological properties. HF cells were not hypertrophied (capacitance, mean+/-SEM, 52+/-3 versus 50+/-4 pF in control). HF increased intrinsic cycle length by 15% and decreased diastolic depolarization rate by 30%, whereas other action potential parameters were unaltered. In HF, the hyperpolarization-activated "pacemaker" current (If) and slow component of the delayed rectifier current (IKs) were reduced by 40% and 20%, respectively, without changes in voltage dependence or kinetics. T-type and L-type calcium current, rapid and ultrarapid delayed rectifier current, transient outward currents, and sodium-calcium exchange current were unaltered. CONCLUSIONS: In single SAN cells of rabbits with HF, intrinsic cycle length is increased as the result of a decreased diastolic depolarization rate rather than a change in action potential duration. HF reduced both If and IKs density. Since IKs plays a limited role in pacemaker activity, the HF-induced decrease in heart rate is attributable to remodeling of If.

Action Potentials↗
PubMed2003

Tissue discontinuities affect conduction velocity restitution: a mechanism by which structural barriers may promote wave break.

BACKGROUND: The mechanism by which structural barriers promote wave break and fibrillation is unclear. Conduction velocity (CV) restitution is an important determinant of wave break. Abnormal CV restitution is associated with ventricular fibrillation in patients with heart disease and arises preferentially in fibrotic myocardium. We hypothesize that tissue discontinuities imposed by structural barriers cause abnormal CV restitution. METHODS AND RESULTS: Tissue discontinuities were simulated in cultures of neonatal rat heart cells grown in 8-armed star patterns. Premature stimulation was applied at the extremity of 1 arm (n=12) while extracellular electrograms were recorded at 24 sites throughout the star. Action potentials were recorded at the following 3 sites: in the stimulated arm and at the discontinuity both proximal to and distal from the star center. Extracellular recordings revealed progressive increases in activation delay (indicative for abnormal CV restitution) only at the discontinuity from arms proximal to the star center. The mean increase in delay was 0.81+/-0.41 ms/10 ms for recording sites proximal to and 3.13+/-0.58 ms/10 ms for sites distal from this discontinuity. Depolarizing currents were determined in single cells during premature stimulation and for voltage configurations similar to those arising at the discontinuity. Both voltage-clamp measurements and computer simulations showed that delay at the discontinuity was associated with biphasic, prolonged activation and delayed inactivation of depolarizing current. CONCLUSIONS: Tissue discontinuities cause abnormal CV restitution. Rapid increase in activation after an initial slow activation and delayed inactivation at the discontinuity lengthen the duration of depolarizing current and cause the abnormal restitution.

Action Potentials↗
PubMed2003

A common polymorphism in KCNH2 (HERG) hastens cardiac repolarization.

OBJECTIVE: Genetic variants of cardiac ion channels may influence cardiac repolarization. Thereby such variants may modulate the penetrance of primary electrical disorders, contribute to differences in susceptibility to drug-induced QT-prolongation between individuals, or contribute to rhythm disturbances in the context of structural heart disease. Since the current encoded by KCNH2 (HERG; I(Kr)) is a primary determinant of repolarization, we conducted association studies between the respective alleles of the common amino acid-changing polymorphism at codon 897 (2690A>C; K897T) within HERG and rate-corrected QT interval (QTc). METHODS AND RESULTS: Association analysis in Caucasian subjects (n=1030) revealed a significant association of this polymorphism with QTc (P=0.0025) with CC homozygotes having a significantly shorter QTc (388.5+/-2.9 ms) compared to AA homozygotes (398.5+/-0.9) and heterozygotes (AC, 397.2+/-1.2). The latter two genotypes were associated with comparable mean QTc's, suggesting that the 2690C-allele is recessive. After stratification by sex, the polymorphism was more predictive of QTc in females (P=0.0021), a finding that was replicated in a second population sample (n=352) from the same ethnic background (P=0.044). To assess whether this polymorphism could represent a 'functional' polymorphism, we compared the biophysical properties of K897- and T897-HERG channels by whole-cell voltage clamp. Compared to the K897 channel, the T897 channel displayed a shift of -7 mV in voltage dependence of activation and increased rates of current activation and deactivation. CONCLUSION: As confirmed in modeling studies, these changes are expected to shorten action potential duration by an increase in I(Kr). This recapitulates the shorter QTc in females homozygous for the 2690C-allele.

Action Potentials↗
PubMed2003

Contribution of sodium channel mutations to bradycardia and sinus node dysfunction in LQT3 families.

One variant of the long-QT syndrome (LQT3) is caused by mutations in the human cardiac sodium channel gene. In addition to the characteristic QT prolongation, LQT3 carriers regularly present with bradycardia and sinus pauses. Therefore, we studied the effect of the 1795insD Na+ channel mutation on sinoatrial (SA) pacemaking. The 1795insD channel was previously characterized by the presence of a persistent inward current (Ipst) at -20 mV and a negative shift in voltage dependence of inactivation. In the present study, we first additionally characterized Ipst over the complete voltage range of the SA node action potential (AP) by measuring whole-cell Na+ currents (INa) in HEK-293 cells expressing either wild-type or 1795insD channels. Ipst for 1795insD channels varied between 0.8+/-0.2% and 1.9+/-0.8% of peak INa. Activity of 1795insD channels during SA node pacemaking was confirmed by AP clamp experiments. Next, Ipst and the negative shift were implemented into SA node AP models. The -10-mV shift decreased sinus rate by decreasing diastolic depolarization rate, whereas Ipst decreased sinus rate by AP prolongation, despite a concomitant increase in diastolic depolarization rate. In combination, moderate Ipst (1% to 2%) and the shift reduced sinus rate by approximately 10%. An additional increase in Ipst could result in plateau oscillations and failure to repolarize completely. Thus, Na+ channel mutations displaying an Ipst or a negative shift in inactivation may account for the bradycardia seen in LQT3 patients, whereas SA node pauses or arrest may result from failure of SA node cells to repolarize under conditions of extra net inward current.

Action Potentials↗
PubMed2002

Ca(2+)-activated Cl(-) current in rabbit sinoatrial node cells.

The Ca(2+)-activated Cl(-) current (I(Cl(Ca))) has been identified in atrial, Purkinje and ventricular cells, where it plays a substantial role in phase-1 repolarization and delayed after-depolarizations. In sinoatrial (SA) node cells, however, the presence and functional role of I(Cl(Ca)) is unknown. In the present study we address this issue using perforated patch-clamp methodology and computer simulations. Single SA node cells were enzymatically isolated from rabbit hearts. I(Cl(Ca)) was measured, using the perforated patch-clamp technique, as the current sensitive to the anion blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). Voltage clamp experiments demonstrate the presence of I(Cl(Ca)) in one third of the spontaneously active SA node cells. The current was transient outward with a bell-shaped current-voltage relationship. Adrenoceptor stimulation with 1 microM noradrenaline doubled the I(Cl(Ca)) density. Action potential clamp measurements demonstrate that I(Cl(Ca)) is activate late during the action potential upstroke. Current clamp experiments show, both in the absence and presence of 1 microM noradrenaline, that blockade of I(Cl(Ca)) increases the action potential overshoot and duration, measured at 20 % repolarization. However, intrinsic interbeat interval, upstroke velocity, diastolic depolarization rate and the action potential duration measured at 50 and 90 % repolarization were not affected. Our experimental data are supported by computer simulations, which additionally demonstrate that I(Cl(Ca)) has a limited role in pacemaker synchronization or action potential conduction. In conclusion, I(Cl(Ca)) is present in one third of SA node cells and is activated during the pacemaker cycle. However, I(Cl(Ca)) does not modulate intrinsic interbeat interval, pacemaker synchronization or action potential conduction.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2002

Atrio-sinus interaction demonstrated by blockade of the rapid delayed rectifier current.

BACKGROUND: Proper pacemaking of the heart requires a specific organization of the sinoatrial (SA) node. The SA node drives the surrounding atrium but needs to be protected from its hyperpolarizing influence, which tends to suppress pacemaker activity. It has been suggested that the hyperpolarizing atrial influence is minimal at the site of the central nodal area. METHODS AND RESULTS: Atrio-sinus interaction was assessed by specific depolarization of the SA node by blocking the HERG-encoded rapid delayed rectifier current (I(K,r)) with the drug E-4031. In the SA node, E-4031 (1 micromol/L) changed action potential configuration drastically but never resulted in pacemaker arrest. In the atrium, E-4031 did not affect the membrane resting potential, thereby leaving the normal hyperpolarizing load on the SA node intact. When the SA node was sectioned into strips and subsequently separated from the atrium, spontaneous electrical activity of the strip containing the primary pacemaker ceased on I(K,r) blockade. When not separated from the atrium, I(K,r) blockade never resulted in pacemaker arrest. A similar effective atrio-sinus interaction was demonstrated in computer simulations. CONCLUSIONS: Our results demonstrate that the atrium provides an effective hyperpolarizing load on the central SA nodal area and is at least one of the controlling mechanisms for normal pacemaking function. The present study can be of help in understanding why patients with long-QT2 syndrome secondary to a mutation in HERG do not show sinus arrest.

Action Potentials↗