BACKGROUNDAdvances in catheter ablation procedures for the treatment of supraventricular arrhythmias have created the need to understand better the morphological and electrophysiological characteristics of the inferior nodal extension (INE) and transitional cellular band (TCB) in the atrioventricular (AV) junctional area.

METHODSFirstly, we observed the histological features of 10 rabbit AV junctional areas by serial sections under light microscopy. Then we recorded the action potentials (APs) of transitional cells (TCs) in the INE, TCBs, AV node, and ordinary right atrial myocytes from the AV junctional area of 30 rabbits using standard intracellular microeletrode techniques.

RESULTSUnder light microscopy, the INE appeared to be mostly composed of transitional cells linking upward to the AV node. Four smaller TCBs originated in the orifice of the coronary sinus, the region between the septal leaflet of the tricuspid valve and the coronary sinus, the inferior wall of the left atrium, and the superior interatrial septum, respectively, all linking to the INE or the AV node. Compared with ordinary atrial myocytes, the AP of the TCs in both the INE and the TCBs had a spontaneous phase 4 depolarization (not present in ordinary atrial myocytes), with a less negative maximum diastolic potential, a smaller amplitude, a slower maximum velocity of AP upstroke, and a longer action potential duration at 50% repolarization (APD50) and at 30% repolarization (APD30). The AP characteristics of these TCs were similar to those of the AV node, except that the velocities of the phase 4 spontaneous depolarization were slower and their action potential durations at 90% repolarization (APD90) were shorter. Moreover, APD50 and APD30 of the TCs of the TCBs were shorter than in the case of TCs of the AV node.

CONCLUSIONSThe TCs of the INE and TCBs are similar to slow response automatic cells. They provide a substrate for slow pathway conduction. In addition, repolarization heterogeneity exists in the AV junctional area.

Action Potentials ; Animals ; Atrioventricular Node ; cytology ; physiology ; Female ; Male ; Rabbits

Discrete radiofrequency lesion at the atrial insertion site of the tendon of Todaro in the perfused rabbit preparation lengthens A-H interval, mimicking fast pathway input ablation. This study attempts to define the cellular electrophysiology of the ablation region prior to and after the elimination of fast AV node conduction. In six superfused rabbit AV node preparations, the cellular electrophysiology around the region of the atrial insertion to the tendon of Todaro was recorded using standard microelectrode technique prior to and after ablation. Before ablation, the action potentials recorded in the area of proposed lesion were exclusively from atrial or AN cells. At postablation, the superior margin of the lesion was populated with atrial or AN cells. AN, N, or NH cells bordered the lower part of the lesion. Electrophysiology of surviving cells at the edges of the lesion showed no significant changes in their Vmax, APD50 or APD90 and MDP from preablation values. Fast AV node pathway input ablation in the rabbit heart can be accomplished with a singular lesion around the atrial insertion site of the tendon of Todaro, involving atrial or AN cells. The results of the studies imply that inputs to the compact node may act as a substrate for successful ablation of AV node reentry tachycardia.
Action Potentials/physiology ; Animal ; Atrioventricular Node/surgery* ; Atrioventricular Node/physiology ; Atrioventricular Node/cytology* ; Catheter Ablation/methods* ; Electrophysiology ; Rabbits ; Recovery of Function ; Tachycardia, Supraventricular/surgery ; Tachycardia, Supraventricular/physiopathology

BACKGROUNDThe morphological and electrophysiological characteristics of cardiac cells in Koch triangle are still disputed. We studied the appearance and electrical properties of these diverse myocytes to elucidate their complex electrophysiological phenomena.

METHODSExperiments were conducted using cooled charge coupling device (CCD) system and whole cell, patch clamp technique to determine the morphology, action potential and sodium current density of single viable myocytes enzymatically isolated from the Koch triangle of rabbit hearts.

RESULTSMorphologically, cardiac cells in shape of spider, tiny spindle, slender spindle, rod and strip were observed in percentage of 3.0 +/- 0.3, 35.0 +/- 5.0, 15.0 +/- 2.0, 40.0 +/- 5.0 and 6.0 +/- 0.7 respectively. The cellular dimensions and capacitance gradually increased in the above order (all P < 0.05). Electrophysiologically, action potential configurations recorded from them were similar respectively to nodal (N), atrial nodal (AN), nodal Hisian (NH), atrial (A) and Hisian like potentials obtained from the intact atrioventricular nodal preparations. Diastolic depolarization appeared in all myocytes except for rod cells. Sodium current density increased in the order of tiny spindle, strip, rod, slender spindle cell (all P < 0.05), but could not be detected in spider-shaped cells. Linear regression analysis revealed that membrane capacitance was correlated negatively to the rate of diastolic depolarization r = -0.70, P < 0.001, but positively to maximum depolarization potential, amplitude of action potential, upstroke velocity and maximum peak value of sodium current density r = 0.84, 0.80, 0.87 and 0.75, respectively; all P < 0.001.

CONCLUSIONSThe results demonstrated that spider-shaped, spindle, rod and strip cells in Koch triangle might correspond to pacemaking, transitional, atrial and Purkinje like cells, respectively. Furthermore, tiny spindle and slender spindle cells were referred to transitional cell alpha (TCalpha) and beta (TCbeta) accordingly considering their distinctive electrical properties. Different myocytes with diverse electrical properties constituted the infrastructure of sophisticated electrophysiological phenomena in Koch triangle. In view of the prominent percentage and electrical properties, tiny spindle and slender spindle cells were presumed to play important roles.

Action Potentials ; Animals ; Atrioventricular Node ; cytology ; physiology ; Female ; Male ; Myocytes, Cardiac ; cytology ; physiology ; Rabbits ; Sodium Channels ; physiology

OBJECTIVETo quantitatively detect the expression of connexins (Cx) mRNA in the posterior nodal extension (PNE) of adult rat heart and understand the relationship between Cx expression and atrial ventricular nodal reentrant tachycardia (AVNRT).

METHODSPNE was separated from adult rat heart by means of laser microdissection (LCM), and the cells were also isolated from the atrioventricular node (AVN), sinoatrial node (SAN), Purkinje fiber (PF), right atrium (RA) and right ventricle (RV), to serve as the controls. The Cx mRNA level was detected in these cells with quantitative real-time PCR (QRT-PCR).

RESULTSThe cells were successfully isolated from the PNE and other regions of adult rat heart, where heterogeneous expression of the 3 Cx isoforms (Cx43, Cx45, and Cx40) were observed. Cx45 mRNA showed higher expression in the PNE than in the working myocardium, whereas Cx43 mRNA level was about 25 times higher (P<0.05) in the working myocardium and 18 times higher (P<0.05) in the PF than in the PNE. In the PF, Cx40 mRNA level was proximately 6.8 times (P<0.01) as much as that in the PNE. Cx expression in the PNE was, however, similar to that in the SAN and AVN.

CONCLUSIONCx mRNAs exhibit heterogeneous expression in the PNE to allow the formation of the slow pathway. In addition, Cx expression in the PNE is very different from that in the adjacent myocardium, resulting in conduction discontinuity at the cellular junction, where, on certain occasion, unidirectional block may occur to cause AVNRT.

Animals ; Atrioventricular Node ; cytology ; metabolism ; Connexin 43 ; genetics ; Connexins ; genetics ; Female ; Male ; Myocardium ; cytology ; metabolism ; Purkinje Fibers ; cytology ; metabolism ; RNA, Messenger ; genetics ; metabolism ; Rats ; Rats, Sprague-Dawley ; Reverse Transcriptase Polymerase Chain Reaction ; Sinoatrial Node ; cytology ; metabolism

The purpose of this study was to determine the electrophysiological effects of genistein (GST) on spontaneous activity of atrioventricular (AV) node and the underlying mechanism(s). Action potentials in AV node cells were recorded using intracellular microelectrode technique. GST not only reduced the amplitude of action potential (APA), maximal rate of depolarization (V(max)), velocity of diastolic (phase 4) depolarization (VDD), and rate of spontaneous firing (RSF), but also prolonged 90% duration of action potential (APD(90)) in a concentration-dependent manner. The effects of GST (50 micromol/L) could be blocked completely by pretreatment with Bay K8644 (0.25 micromol/L), an agonist of L-type calcium channel. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 0.5 mmol/L), a nitric oxide (NO) synthase inhibitor, did not affect the effects of GST on AV node cells. Elevation of Ca(2+) concentration (5 mmol/L) in superfusate antagonized the effects of GST (50 micromol/L). These results suggest that GST exerted a negative electrophysiological effects of spontaneous activity of AV node cells in rabbits. These effects were likely due to reduction in calcium influx, but had no association with NO release.
Action Potentials ; drug effects ; Animals ; Atrioventricular Node ; cytology ; physiology ; Calcium Channels ; drug effects ; Dose-Response Relationship, Drug ; Genistein ; pharmacology ; Male ; Phytoestrogens ; pharmacology ; Rabbits

OBJECTIVETo observe the changes of surface ECG and cell couplings between sinoatrial node cells and myocardial cells following transplantion of pedicled autologous sinoatrial node tissue graft into the right ventricle of a canine model of complete atrioventricular block.

METHODSTen healthy dogs were randomized into transplantation group and control group. Pedicled autologous sinoatrial node tissue grafts were transplanted into the right ventricle in the transplantation group, while the sinoatrial nodes were only excised in the control group after placement of temporary myocardial pacing wires. The changes of surface ECG were observed at 1, 2, 3 and 4 weeks postoperatively. At 4 weeks, complete atrioventricular block was induced in the dogs by radiofrequency ablation of the His bundle. The heart rate of the dogs in both groups were recorded after the injection of isoproternol (ISO) from the femoral vein, and the transplanted tissue graft was observed under optical and transmission electron microscopes.

RESULTSNo significant changes occurred in the surface ECG. All the dogs showed ECG waveforms specific of complete heart block after the ablation, and the ventricular heart rates were similar between the two groups (P>0.05). The ventricular heart rate did not undergo obvious changes after ISO injection (P>0.05). The transplanted pedicled autologous sinoatrial node survived in the dogs and the sinoatrial node cells established desmosome junctions with the myocardial cells, but the number of junctions was not sufficient to support heart pacing.

CONCLUSIONDesmosome junction can occur between ventricular myocardial cells and sinoatrial node cells at the edge of transplanted pedicled autologous sinoatrial node tissue.

Animals ; Atrioventricular Block ; physiopathology ; surgery ; Cardiotonic Agents ; pharmacology ; Dogs ; Electrocardiography ; Female ; Heart Rate ; drug effects ; Heart Ventricles ; surgery ; Intercellular Junctions ; Isoproterenol ; pharmacology ; Male ; Myocardium ; cytology ; Sinoatrial Node ; cytology ; transplantation ; Tissue Transplantation ; Transplantation, Autologous

The electrophysiological effects of nitric oxide (NO) on spontaneous activity of rabbit atrioventricular (AV) node cells were examined using intracellular microelectrode technique. The results obtained are as follows. (1) NO donors sodium nitroprusside (SNP, 1~1000 micromol/L) and 3-morpholinosydnonimine (SIN-1, 100, 1000 micromol/L) decreased the amplitude of action potential (APA), rate of spontaneous firing (RSF), velocity of diastolic (phase 4) depolarization (VDD), and maximal rate of depolarization (V(max)) in a concentration-dependent manner. (2) Pretreatment with L-type calcium channel agonist Bay K8644 (0.25 micromol/L) completely reversed the effects of SNP (100 micromol/L) on AV node cells. (3) Elevation of Ca(2+) concentration (5 mmol/L) in superfusate antagonized the effects of SNP on AV node cells. (4) Perfusion with Ca(2+)-free K-H solution, completely abolished the effects of SNP on AV node cells. (5) Application of methylene blue (50 micromol/L), a guanylyl cyclase inhibitor, failed to abolish the inhibitory effects of SNP (100 micromol/L). All these results suggest that NO exerts a negative effect on spontaneous activity of AV node cells in rabbits. These effects are likely due to reduction in calcium influx via a cGMP-independent mechanism.
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester ; pharmacology ; Action Potentials ; drug effects ; Animals ; Atrioventricular Node ; cytology ; physiology ; Calcium ; metabolism ; Calcium Channel Agonists ; pharmacology ; Calcium Channels, L-Type ; metabolism ; Depression, Chemical ; Female ; Male ; Microelectrodes ; Nitric Oxide ; physiology ; Rabbits

To study the electrophysiological effects of capsaicin on spontaneous activity of rabbit atrioventricular (AV) node cells, parameters of action potential in AV node were recorded using intracellular microelectrode technique. Capsaicin (1-30 micromol/L) not only decreased the amplitude of action potential, maximal rate of depolarization (V(max)), velocity of diastolic (phase 4) depolarization, and rate of pacemaker firing, but also prolonged the duration of 90% repolarization of action potential (APD(90)) in a concentration-dependent manner. Both application of L-type Ca(2+) channel agonist Bay K8644 (0.5 micromol/L) and elevation of calcium concentration (5 mmol/L) in superfusate antagonized the effects of capsaicin on pacemaker cells. Pretreatment with ruthenium red (10 micromol/L), a capsaicin receptor blocker, did not affect the effects of capsaicin on AV node cells. Capsaicin exerted an inhibitory action on spontaneous activity of AV node cells in rabbits. These effects were likely due to reduction in calcium influx, but were not mediated by VR1.
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester ; pharmacology ; Action Potentials ; drug effects ; Animals ; Atrioventricular Node ; cytology ; physiology ; Calcium ; metabolism ; Calcium Channel Agonists ; pharmacology ; Calcium Channels, L-Type ; drug effects ; Capsaicin ; pharmacology ; Male ; Microelectrodes ; Rabbits ; Receptors, Drug ; antagonists & inhibitors ; Ruthenium Red ; pharmacology