Light trimming of a narrow bandpass filter based on a photosensitive chalcogenide spacer.

We present an experimental study of the photosensitive properties of a narrow bandpass filter based on a Ge(15)Sb(20)S(65) spacer fabricated by electron beam deposition. For a single layer, near the optical bandgap of this chalcogenide material, the efficiency of the photo-bleaching increases as the central wavelength of the light source for exposure decreases. The maximum relative photo-induced change of the optical thickness reaches about 1%. By using controlled light exposure around 480 nm of a photosensitive narrow bandpass filter centered at 1550 nm, we obtained a spatially localized shift of its peak wavelength up to 5.4 nm. This property is used to perform, for the first time at our knowledge, the post trimming of a narrow bandpass filter with a light beam. A 5 x 5 mm(2) ultra uniform area in which the relative spatial variation of its peak wavelength remains below 0.004% is demonstrated.

Functional beta3-adrenoceptor in the human heart.

Beta3-adrenoceptors are involved in metabolism, gut relaxation, and vascular vasodilation. However, their existence and role in the human heart have not been documented. We investigated the effects of several beta-adrenoceptor agonists and antagonists on the mechanical properties of ventricular endomyocardial biopsies. In the presence of nadolol, a beta1- and beta2-adrenoceptor antagonist, isoprenaline produced consistent negative inotropic effects. Similar negative inotropic effects also resulted from the action of beta3-adrenoceptor agonists with an order of potency: BRL 37344 > SR 58611 approximately CL 316243 > CGP 12177. The dose-response curve to BRL 37344-decreasing myocardial contractility was not modified by pretreatment with nadolol, but was shifted to the right by bupranolol, a nonselective beta-adrenoceptor antagonist. Beta3-adrenoceptor agonists also induced a reduction in the amplitude and an acceleration in the repolarization phase of the human action potential. Beta3-adrenoceptor transcripts were detected in human ventricle by a polymerase chain reaction assay. These results indicate that: (a) beta3-adrenoceptors are present and functional in the human heart; and (b) these receptors are responsible for the unexpected negative inotropic effects of catecholamines and may be involved in pathophysiological mechanisms leading to heart failure.

Amiodarone reduces transmural heterogeneity of repolarization in the human heart.

OBJECTIVES: The present work was designed to test the effects of amiodarone therapy on action potential characteristics of the three cell types observed in human left ventricular preparations. BACKGROUND: The electrophysiologic basis for amiodarone's exceptional antiarrhythmic efficacy and low proarrhythmic profile remains unclear. METHODS: We used standard microelectrode techniques to investigate the effects of chronic amiodarone therapy on transmembrane activity of the three predominant cellular subtypes (epicardial, midmyocardial [M] and endocardial cells) spanning the human left ventricle in hearts explanted from normal, heart failure and amiodarone-treated heart failure patients. RESULTS: Tissues isolated from the ventricles of heart failure patients receiving chronic amiodarone therapy displayed M cell action potential duration (404+/-12 ms) significantly briefer (p < 0.05) than that recorded in tissues isolated from normal hearts (439+/-22 ms) or from heart failure patients not treated with amiodarone (449+/-18 ms). Endocardial cells from amiodarone-treated heart failure patients displayed longer (p < 0.05) action potential duration (363+/-10 ms) than endocardial cells isolated from normal hearts (330+/-6 ms). As a consequence, the heterogeneity of ventricular repolarization in tissues from patients treated with amiodarone was considerably smaller than in the two other groups, especially at long pacing cycle lengths. CONCLUSIONS: These findings may explain, at least in part, the reduction of ventricular repolarization dispersion and the lower incidence of torsade de pointes observed with chronic amiodarone therapy as compared with other class III agents.

Electrophysiologic characteristics of cells spanning the left ventricular wall of human heart: evidence for presence of M cells.

OBJECTIVES: The present work was designed to provide an initial characterization of M cells in the normal human heart. BACKGROUND: Recent studies have uncovered a unique population of cells in the midmyocardial region of the canine ventricle. These cells, named M cells, were found to possess electrophysiologic features and a pharmacologic responsiveness different from those of other myocardial cells. Although well characterized in the dog, their presence or absence in the human heart is unknown. METHODS: Standard microelectrode techniques were used to map slices of ventricular free wall obtained from normal human hearts (n = 4). Preparations were paced at cycle lengths ranging from 1 to 10 s. RESULTS: We identified three cell subtypes: endocardial, subepicardial (M cells) and epicardial cells. The principal features differentiating M cells from the other cell subtypes were their longer action potential duration, more accentuated action potential duration rate relations and greater maximal rate of increase in action potential upstroke (Vmax). Our findings suggest that M cells represent approximately 30% of the cellular mass of the left ventricular wall. Concordance between changes in their repolarization and changes in QTU interval provide support for the role of M cells in the generation of the electrocardiographic (ECG) U wave. CONCLUSIONS: This study provides evidence for the existence of M cells in the human heart that contribute to heterogeneity of repolarization within the ventricular wall. Our findings provide strong support for the hypothesis that M cells contribute importantly to the manifestation of the U wave on the ECG.

Electropharmacological characterization of cardiac repolarization in German shepherd dogs with an inherited syndrome of sudden death: abnormal response to potassium channel blockers.

OBJECTIVES: This study sought to determine whether abnormal ventricular repolarization is implicated in cardiac arrhythmias of German shepherd dogs with inherited sudden death. BACKGROUND: Moïse et al. (9) have identified German shepherd dogs that display pause-dependent lethal ventricular arrhythmias. METHODS: Ventricular repolarization was studied both in vivo using electrocardiogram recordings on conscious dogs and in vitro with a standard microelectrode technique performed on endomyocardial biopsies and Purkinje fibers. Pharmacological manipulation was used to evaluate the role of potassium channels. RESULTS: In control conditions, electrocardiogram parameters were similar in both groups of dogs, except for the PR interval (18% longer in affected dogs, p < 0.05). Injection of d,l-sotalol (2 mg/kg) prolonged QT interval more in affected dogs (+14%, n = 9) than it did in unaffected dogs (+6%, n = 6, p < 0.05) and increased the severity of arrhythmias in affected dogs. In vitro, in control conditions, action potential duration (APD90) of endomyocardial biopsies and Purkinje fibers were significantly longer in affected dogs (respectively 209 +/- 3 ms, n = 30 and 352 +/- 15 ms, n = 17) than they were in unaffected dogs (197 +/- 4 ms, n = 25 and 300 +/- 9 ms, n = 30) at a pacing cycle length (PCL) of 1,000 ms. This difference increased with PCL. The kinetics of adaptation of APD90 to a change in PCL was faster in affected dogs. D,l-sotalol (10(-5) and 10(-4)M) increased APD90 in both groups of dogs, but this increase was greater in affected dogs, with the occurrence of triggered activity on Purkinje fibers. E-4031 (10(-7) and 10(-6) M), an I(Kr)-blocker, increased APD90 similarly in both groups of dogs. Chromanol 293B (10(-6) and 10(-5)M), an I(Ks)-blocker, increased significantly APD90 in unaffected dogs but had no effect in affected dogs. CONCLUSIONS: These results support the hypothesis of an abnormal cardiac repolarization in affected dogs. The effects of 293B suggest that I(Ks) may be involved in this anomaly.

Effects of chronic treatment by amiodarone on transmural heterogeneity of canine ventricular repolarization in vivo: interactions with acute sotalol.

OBJECTIVE: The present study was designed to examine the effects of chronic amiodarone on the different ventricular cell subtypes in situ and to evaluate its interactions with sotalol. METHODS: Three groups of dogs were studied. Group I (n = 8) received no treatment. Group II (n = 7) and group III (n = 8) received, respectively, 100 and 200 mg amiodarone orally twice a day for 6 weeks to 8 months. In vivo studies were performed under halothane anesthesia 14 h after the last administration of amiodarone. Three leads ECG, femoral blood pressure and left ventricular intramural monophasic action potentials (MAP) were continuously recorded. Bradycardia was obtained by clamping the sinus node and beta-blockade and the heart was driven by atrial pacing. Three weeks before the in vivo experiments, the cellular electrophysiologic properties of right ventricular tissues obtained by cardiac biopsy in six treated and six control dogs were studied with standard microelectrodes. RESULTS: Amiodarone produced a dose-dependent decrease in plasma levels of triiodothyronine (T3; 5.9 +/- 0.4 pM in control dogs, 3.1 +/- 0.2 pM in group III, P < 0.001) without affecting thyroxine (T4). Under anesthesia, the QT interval was 14% larger in group III compared to group I at a paced cycle length (PCL) of 1500 ms (P < 0.05). This is consistent with the 10% increase in endocardial MAP duration in group III at the same PCL (P < 0.05). There was no significant increase in transmural dispersion of MAP duration. In group I, sotalol induced a significant reverse use-dependent increase in MAP duration. This effect was reduced in group II and completely suppressed in group III. Amiodarone prevented the sotalol-induced increase in transmural dispersion of ventricular repolarization which was 69 +/- 12 ms in untreated dogs, 41 +/- 8 ms in group II (P < 0.05) and 34 +/- 8 ms (P < 0.05) in group III at PCL = 1500 ms. Amiodarone also prevented the sotalol-induced ventricular tachyarrhythmias. In vitro, the action potential duration was longer in amiodarone-treated dogs that in control ones (208 +/- 5 ms versus 188 +/- 9 ms at PCL = 1000 ms, P < 0.05). The sotalol-induced prolongation of repolarization was reduced in amiodarone-treated dogs. CONCLUSION: Chronic treatment of dogs with amiodarone induced a moderate prolongation of the QT interval and MAP duration without affecting transmural dispersion of repolarization and inhibited the effects of acute sotalol, including the prolongation of repolarization, the increase in transmural dispersion of repolarization and the induction of arrhythmias.

Transgenic mice overexpressing human KvLQT1 dominant-negative isoform. Part II: Pharmacological profile.

OBJECTIVE: The acquired long QT syndrome results most often from the action of I(Kr) blocking-drugs on cardiac repolarization. We have evaluated a transgenic (TG) mouse (FVB) overexpressing a dominant-negative KvLQT1 isoform, as an in vivo screening model for I(Kr) blocking drugs. RESULTS: In TG mice, six-lead ECGs demonstrated sinus bradycardia, atrioventricular block, and QTc prolongation. Various drugs were injected intraperitoneally after blockade of the autonomic nervous system and serial ECGs were recorded. The end of the initial rapid phase of the T wave corrected for heart rate using a formula for mouse heart (QTrc), was used as a surrogate for the QT interval. Dofetilide, a specific I(Kr) blocker, did not prolong the QTrc interval either in TG or in wild-type (WT) mice but dose-dependently lengthened the sinus period in TG mice but not in WT mice. Other I(Kr) blockers including E 4031, haloperidol, sultopride, astemizole, cisapride and terikalant behaved similarly to dofetilide. Tedisamil, a blocker of the transient outward current, dose-dependently prolonged the QTrc in WT mice but not in TG mice and also reduced the sinus rhythm in both WT and TG mice. Lidocaine dose-dependently shortened the QTrc interval in TG mice and also lengthened the P wave duration. Nicardipine dose-dependently shortened QTrc and also produced sinus arrest in both WT and TG mice. CONCLUSIONS: We conclude that KvLQT1-invalidated TG mice discriminates in vivo drugs that blocks I(Kr) from drugs that block the transient outward current, the sodium current or the calcium current.

Abnormal cardiac repolarization and impulse initiation in German shepherd dogs with inherited ventricular arrhythmias and sudden death.

OBJECTIVE: We tested the hypothesis that delayed afterdepolarization (DAD)-associated rhythms in German shepherd dogs with reduced anteroseptal left ventricular (LV) sympathetic innervation derive from abnormal beta-adrenergic receptor effector coupling. METHODS AND RESULTS: In anteroseptal LV midmyocardium of afflicted dogs, beta-receptor density was greater than that in normal dogs (P < .05), with affinity being equal in both groups. Basal and maximum isoproterenol (ISO) stimulated adenylyl cyclase activity of anteroseptal LV of afflicted dogs was greater than that in normal dogs (P < .05). Isolated anteroseptal M cell preparations of afflicted dogs studied with microelectrodes showed abnormal lengthening, rather than shortening of action potential duration in response to ISO, as well as a 61% incidence of 10(-7) mol/l ISO-induced triggered activity as compared to 12% in normals (P < .05). In contrast, there was no difference between afflicted and control dogs in triggered activity, beta-receptors or adenylyl cyclase activity in a normally innervated region of the ventricles. CONCLUSION: In this model there is an increase in beta-receptor density and beta-adrenergic stimulation of adenylyl cyclase and of triggered activity in anteroseptal myocardium but not in a normally innervated region of the heart. Hence, abnormal beta-adrenergic signal transduction appears associated with the neural abnormality identified in dogs with inherited VT.

Transgenic mice overexpressing human KvLQT1 dominant-negative isoform. Part I: Phenotypic characterisation.

OBJECTIVES: The KCNQ1 gene encodes the KvLQT1 potassium channel, which generates in the human heart the slow component of the cardiac delayed rectifier current, I(Ks). Mutations in KCNQ1 are the most frequent cause of the congenital long QT syndrome. We have previously cloned a cardiac KCNQ1 human isoform, which exerts a strong dominant-negative effect on KvLQT1 channels. We took advantage of this dominant-negative isoform to engineer an in vivo model of KvLQT1 disruption, obtained by overexpressing the dominant-negative subunit under the control of the alpha-myosin heavy chain promoter. RESULTS: Three different transgenic lines demonstrated a phenotype with increasing severity. Functional suppression of KvLQT1 in transgenic mice led to a markedly prolonged QT interval associated with sinus node dysfunction. Transgenic mice also demonstrated atrio-ventricular block leading to occasional Wenckebach phenomenon. The atrio-ventricular block was associated with prolonged AH but normal HV interval in His recordings. Prolonged QT interval correlated with prolonged action potential duration and with reduced K(+) current density in patch-clamp experiments. RNase protection assay revealed remodeling of K(+) channel expression in transgenic mice. CONCLUSIONS: Our transgenic mouse model suggests a role for KvLQT1 channels not only in the mouse cardiac repolarisation but also in the sinus node automaticity and in the propagation of the impulse through the AV node.

Immunotherapy with interleukin-2 (IL2) and lymphokine-activated natural killer cells: improvement of clinical responses in metastatic renal cell carcinoma patients previously treated with IL2.

Treatment with interleukin-2 (IL2) induces clinical responses in 15-30% of metastatic renal cell carcinoma (MRCC) patients, with mainly partial responses. In order to improve clinical response, we decided to treat partial response patients from a previous IL2 treatment with a second course of IL2 associated with lymphokine-activated natural killer (LANAK) cells. 10 patients who underwent PR after an IL2 protocol (24 x 10(6) U/m2/day, 2 days a week for 5 weeks, either alone or with interferon-gamma) subsequently received a combination of high-dose IL2 (16-20 x 10(6) U/m2/day, 2 days a week) and LANAK cell infusions. Four complete responses were obtained, and 2 additional patients whose tumour mass was further reduced achieved complete response following surgery. These results support the view that initial responses obtained with primary IL2 courses can be improved by complementary treatments. The potential role of cellular immunotherapy and, more particularly, of LANAK cells as an effective procedure to further reduce tumour burden in patients responsive to IL2 will have to be assessed in randomised studies.

Early after/depolarizations and triggered activity: mechanisms and autonomic regulation.

An early after/depolarization (EAD) is an abnormality of the repolarization process of an action potential which causes an interruption or a retardation of normal repolarization. Two types were described: phase 3 EADs occur at a takeoff potential of approximately-60 mV and phase 2 EADs occur at the end of a prolonged plateau at a takeoff potential of between-10 and-30 mV. EADs can result from an increase in inward current, a reduction of outward current or both. EADs show cycle-length dependence: as cycle length increases and repolarization lengthens, EADs occur, and their magnitude increases, at a critical cycle length, can trigger the action potential of these EADs. The autonomic nervous system can also modulate EADs and trigger activity. In cesium-intoxicated Purkinje fibers, beta-adrenergic stimulation increases EAD magnitude and the occurrence of triggered activity. Cholinergic stimulation decreases EAD magnitude and suppresses triggered activity occurring after beta-adrenergic stimulation. Alpha 1-adrenergic stimulation has no effect on phase 3 EADs but induces phase 2 EADs. In normal Tyrode's solution (0 cesium), phenylephrine prolongs action potential and induces EADs. This effect seems to depend on alpha 1 A stimulation. These electrogenic abnormalities are supposed to be responsible for long QT and torsades de pointes. As our experimental data have shown that both the rate of stimulation and the autonomic nervous system could modulate EADs and trigger activity, we can speculate on the therapeutic implications of such modulations and the role of pacing as well as alpha- and beta-adrenergic antagonists.

[Effects of magnesium on early post-depolarization and trigger activity induced by cesium on Purkinje fibers in ferrets]. / Effets du magnésium sur les post-dépolarisations précoces et l'activité déclenchée induites par le césium sur les fibres de Purkinje de furet.

The effects of magnesium (Mg) on afterdepolarisations and cesium-induced activity were studied in 15 preparations of ferret Purkinje fibres. When the perfusion medium was enriched with Mg to concentrations of 5 mM, the duration of the action potentials stopped increasing and the diastolic membrane potential was stabilised despite persistent exposure to cesium. A suppressor effect of Mg on the high and low voltage early afterdepolarisations was observed which was significant at 2.2 mM (p less than 0.03) and even more so at 5 mM (p = 3. 10-5) related to a lower probability of early afterdepolarisations. A suppressor effect of Mg on high and low voltage induced activities was also recorded, significant at 5 mM, due to a reduction in the probability of apparition of a first induced action potential (p = 2. 10-4) and a reduction in the number of induced action potentials (p = 8. 10-4). The rapid onset of action (a few minutes) of Mg suggests an extracellular mode of action. The suppressor effect of Mg is probably related to inhibition of an unmasked current by the cesium, a calcium antagonist effect and/or non-specific membrane stabilising effect. The suppressor effect of Mg on early afterdepolarisations and induced activity could, at least partially, explain its in vito antiarrhythmic action on torsades de pointe.

[QT interval and drugs. Recommendation for drug prescription for patients with long QT syndrome. Clinical Research Group of INSERM 4940 12: Diagnostic Clinic of Congenital Long QT Syndrome]. / Intervalle QT et médicaments. Recommandations pour la prescription des médicaments chez les patients atteints du syndrome de QT long. Les Membres du Réseau de Recherche Clinique INSERM 4940 12: "Génétique, Physiopathologie et Diagnostic Clinique du Syndrome du QT long Congénital".

The genetics of the long QT syndrome are now better understood. However, there is much heterogeneity as three different genes have already been identified affecting the function of sodium and potassium channels. The aim of these recommendations is to draw up a list of drugs which are contraindicated or not recommended in patients with congenital long QT syndromes. The conraindicated drugs are those with which torsades de pointe have already been described. Drugs not recommended are substances which are not electrohysiologically neutral and for which, in view of their modes of action, their metabolism or belonging to a particular therapeutic class, make them very difficult to use in those patients. It is therefore better not to prescribe them whenever possible in this condition. These substances belong mainly to cardiovascular (especially antiarrhythmic), psychotropic, anti-infectious and antiallergic groups of drugs.

[Blood donation in urban areas]. / La collecte en milieu urbain (Maisons Du Don, sociologie).

Medical and technical developments increase the difficulty to provide sufficient safe blood for all patients in developed countries and their sociodemographic and societal changes. Sufficient national blood supply remains a reached, however still actual, challenge. Tomorrow is prepared today: the management of blood donation programs both in line with these developments and with social marketing strategies is one of the keys to success. If the main components of this organization are well known (mobile blood drives in various appropriate environments, and permanent blood donation centers) their proportions in the whole process must evolve and their contents require adaptations, especially for whole blood donation in urban areas. We have to focus on the people's way of life changes related to increasing urbanization of the society and prominent position taken by very large cities. This requires targeting several goals: to draw the attention of the potential blood-giving candidate, to get into position to collect him when he will decide it, to give meaning and recognition to his "sacrifice" (give time rather than donate blood) and to give him desire and opportunity to come back and donate one more time. In this strategy, permanent blood centers in urban areas have significant potential for whole blood collection, highlighted by the decrease of apheresis technology requirements. This potential requires profound changes in their location, conception and organization. The concept of Maison Du Don (MDD) reflects these changes.

alpha1-adrenergic stimulation induces early afterdepolarizations in ferret Purkinje fibers.

The aim of this study was to evaluate whether alpha1-adrenergic stimulation, which prolongs repolarization, could induce early afterdepolarizations (EADs) in ferret Purkinje fibers. We used standard microelectrodes to study the effects of phenylephrine 10(-6)M in the presence of metoprolol 1.5 x 10(-6)M, on action potentials (AP) recorded from isolated ferret Purkinje fibers superfused with normal Tyrode's solution. Phenylephrine induced a time-dependent prolongation of the AP duration at 60 and 90% of full repolarization (APD60, APD90) from 223 +/- 8 and 269 +/- 9 ms, respectively, during control to 279 +/- 11 and 329 +/- 12 ms after 1-h superfusion (n = 29; p < 0.05 vs. control for both parameters) and 334 +/- 13 and 385 +/- 15 ms after 4 h (n = 29, p < 0.05 vs. control and 1-h superfusion for both parameters) without changing the other parameters. About one third of the fibers studied developed EADs that could be either phase 2 or phase 3 EADs. The alpha1-adrenoceptor antagonist WB 4101 (10(-7)M) limited the AP prolongation and prevented the occurrence of EADs. On the other hand, the alpha1-adrenoceptor alkylating agent chloroethylclonidine (10(-7)M) had no effect. The calcium chelator BAPTA [1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetra-acetic acid] (2 x 10(-3)M) did not prevent the induction of EADs by phenylephrine, although it suppressed the twitch tension, showing that it did chelate the intracellular calcium. Our results show that alpha1-adrenergic stimulation prolongs repolarization in ferret Purkinje fibers and can induce EADs. This effect is mainly mediated by the WB 4101-sensitive alpha1-adrenoceptors (alpha1A- and/or alpha1C-adrenoceptors) and does not depend on intracellular calcium. alpha1-Adrenergic stimulation may have arrhythmogenic effects in patients with long QT syndrome (LQTS).

Beta-adrenergic regulation of action potentials and automaticity in young and adult canine purkinje fibers.

To investigate developmental changes in the cellular electrophysiological effects of beta 1- and beta 2-adrenoceptor stimulation on canine Purkinje fibers (PF), we studied the effects of isoproterenol, a nonselective beta-agonist, and salbutamol, a preponderantly beta 2-agonist, alone or in presence of the selective beta 1-antagonist CGP-20712A or the beta 2-antagonist ICI-118551. Standard microelectrode techniques were used to study adult and neonatal (< 11 days) PF paced at a cycle length of 1 s or allowed to beat spontaneously. In paced adult PF, isoproterenol significantly increased the maximum diastolic potential and significantly decreased action potential duration at 60 and 90% of full repolarization (APD60 and APD90) in a concentration-dependent fashion. These effects were not observed in neonatal PF, which instead manifested a significant increase in phase 2 amplitude and APD30 that was not observed in adult PF. All these effects occurred as well with salbutamol but were less pronounced and required higher agonist concentrations. Isoproterenol decreased the automatic cycle length of adult fibers from 4,079 +/- 796 ms during control to 2,190 +/- 229 ms at 10(-5) M (P < 0.05) and from 1,535 +/- 105 to 1,249 +/- 90 ms in neonatal PF (P < 0.05). In both adults and neonates, > 90% of this effect was reached at a concentration of 10(-8) M. Salbutamol had the same effect but required higher concentrations. In both adults and neonates, the beta 2-antagonist ICI-118551 did not modify any of the effects of isoproterenol and salbutamol, whereas the beta 1-antagonist CGP-20712A significantly antagonized them. In conclusion, 1) the effects of beta-adrenergic stimulation on transmembrane potentials of canine PF change during development, both qualitatively (in paced PF) and quantitatively (in automatic PF) and 2) the responses seen are attributable to the activation of beta 1- and not beta 2-adrenoceptors.

Triggered activity as a possible mechanism for arrhythmias in ventricular hypertrophy.

To study the cellular mechanisms of arrhythmias occurring in cardiac hypertrophy, we performed standard microelectrode studies on papillary muscles isolated from control (group N) and hypertrophied ferrets right ventricles. Different stages of hypertrophy, induced by pulmonary banding, were studied: 10-22 days (group H1), 4-6 weeks (H2), and 5 1/2-6 months (H3). During the development of hypertrophy, under beta-adrenergic stimulation, triggered activity (TA) induced by delayed afterdepolarizations appeared in 2 of 5 muscles in group H1 and 8 of 8 in group H2. This arrhythmia was absent in N muscles, as well as in H3, despite a pronounced prolongation of the action potentials at 50% (100 +/- 9.3 msec in group H3 vs 67 +/- 5.7 msec in H2; P less than 0.01) and 90% of repolarization (225 +/- 8.7 in H3 vs 185 +/- 7.4 msec in H2; P less than 0.02). The presence of TA was associated with an increase in the intracellular calcium activity (144 +/- 60 nM in H2 vs 47 +/- 9 nM in N; P less than 0.05). TA properties were as follows. Triggering frequency increased as beta-adrenergic stimulation increased, as pacing cycle length (PCL) decreased, and as duration of the prestimulative pause increased. The duration of salvos of TA increased as duration of the prestimulative pauses increased (NS). The coupling interval of the first triggered beat decreased as PCL decreased (P less than 0.001). The minimal cycle length of salvos of TA was not modified by these parameters. It is concluded that delayed afterdepolarizations-induced TA may occur under beta-adrenergic stimulation during the first stages of ventricular hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphatidylinositol-4,5-bisphosphate, PIP2, controls KCNQ1/KCNE1 voltage-gated potassium channels: a functional homology between voltage-gated and inward rectifier K+ channels.

Phosphatidylinositol-4,5-bisphosphate (PIP(2)) is a major signaling molecule implicated in the regulation of various ion transporters and channels. Here we show that PIP(2) and intracellular MgATP control the activity of the KCNQ1/KCNE1 potassium channel complex. In excised patch-clamp recordings, the KCNQ1/KCNE1 current decreased spontaneously with time. This rundown was markedly slowed by cytosolic application of PIP(2) and fully prevented by application of PIP(2) plus MgATP. PIP(2)-dependent rundown was accompanied by acceleration in the current deactivation kinetics, whereas the MgATP-dependent rundown was not. Cytosolic application of PIP(2) slowed deactivation kinetics and also shifted the voltage dependency of the channel activation toward negative potentials. Complex changes in the current characteristics induced by membrane PIP(2) was fully restituted by a model originally elaborated for ATP-regulated two transmembrane-domain potassium channels. The model is consistent with stabilization by PIP(2) of KCNQ1/KCNE1 channels in the open state. Our data suggest a striking functional homology between a six transmembrane-domain voltage-gated channel and a two transmembrane-domain ATP-gated channel.

Age-related differences in beta-adrenergic regulation of repolarization in canine epicardial myocytes.

Developmental changes occur in beta-adrenergic modulation of repolarization in canine. Purkinje fibers that may have important implications for rhythm and arrhythmias. No comparable data exist for ventricular myocardium. Therefore, we studied developmental changes in beta-adrenergic regulation of repolarization and delayed rectifier potassium current (IK) in canine ventricular epicardium. We first investigated the effects of isoproterenol (Iso) on action potentials (AP) recorded from epicardial slices with standard microelectrodes, and then we further determined the mechanisms of Iso action using the nystatin-perforated patch technique on isolated epicardial myocytes. In microelectrode studies Iso (10(-7) M) induced a shortening of the AP in preparations from adult dogs but not in those from dogs < 30 days old. These results were confirmed on AP recorded from single myocytes. Although the plateau was increased by Iso at all ages, the AP at 90% of repolarization was shortened (P < 0.05, n = 6) in adult but unchanged in < 30-day-old myocytes (NS, n = 6). Voltage-clamp studies showed that IK of adult cells was increased from a control value of 10.23 +/- 1.87 to 13.43 +/- 1.92 pA/pF with Iso (step to +50 mV, P < 0.05, n = 6), but IK was not modified in cells from young animals (6.49 +/- 2.72 pA/pF in control and 6.56 +/- 2.62 pA/pF with Iso, n = 4). Increasing the Iso concentration to 10(-5) M failed to increase IK significantly (n = 4). However, 10(-7) M Iso did increase L-type Ca2+ current from 172 +/- 31 to 262 +/- 42 pA (P < 0.05, n = 4), consistent with the effect to increase the AP plateau. These results show that there are developmental changes in beta-adrenergic regulation of repolarization in canine epicardium and that the control site of developmental changes is in the IK channel rather than the beta-adrenergic receptor cascade.