OBJECTIVETo investigate the general pattern of cholinergic nerve distribution and M(2) receptors in adult rat heart.

METHODSKarnovsky-Roots histochemical staining combining point counting method and immunochemical SABC method with image analysis were used to identify the cholinergic nerves and M(2) receptors, respectively, in adult rat heart.

RESULTSPositive staining of cholinergic nerves and M(2) receptors was found in all regions of the rat heart, and the point count of cholinergic nerves in the atria was 4.6 times as much as that in ventricles, and the area of immunoreactive substance for M(2) receptors two-fold higher in the atria than in the ventricles. The point counts of the cholinergic nerves in the medial-layer myocardium were fewer than that in subepicardial and endocardial tissues of the left ventricular free wall. However, M(2) receptors were comparable among the 3 layers of the left free ventricular wall.

CONCLUSIONCholinergic nerves and M(2) receptors are located in both rat atria and ventricles, but their density is much higher in the atria than in the ventricles. Transmural heterogeneity characterizes cholinergic nerve innervation in the left ventricular free wall without significant differences in M(2) receptor density.

Animals ; Cholinergic Fibers ; metabolism ; Female ; Heart ; innervation ; Heart Atria ; innervation ; metabolism ; Heart Ventricles ; innervation ; metabolism ; Immunohistochemistry ; Male ; Myocardium ; metabolism ; Rats ; Rats, Sprague-Dawley ; Receptor, Muscarinic M2 ; analysis

OBJECTIVEElectrical and structural remodeling are of importance for the occurrence and maintenance of atrial fibrillation. We observed association between atrial connexin protein expression and fibrosis in a canine model of prolonged rapid atrial pacing.

METHODS"J"-type electrodes were placed in the right atrial appendage under the guidance of X-ray in 16 dogs, Animals in model group (n = 8) received fast pacing (400 beats/min) for 10 weeks while animals in control group (n = 8) maintained at sinus rhythm. Limb-lead ECGs were recorded at 2, 4, 6, 8 weeks respectively. Burst stimulation was applied to induce atrial fibrillation in all animals after 10 weeks, animals were sacrificed thereafter and the left atrial tissues were taken for myocardial collagen measurement (Masson staining) and myocardial ultrastructure examination and detection of protein expression of connexin (Cx) 40 and 45 (immune staining). Procollagen type III N-terminal peptide and type IV collagen in serum were also detected by radioimmunoassay.

RESULTSTwo dogs died in model group due to atrial rupture induced cardiac tamponade or lung emboli. Spontaneously atrial fibrillation was not observed in all animals, but two dogs developed atrial flutter and atrial premature beats. Atrial fibrillation was induced by burst stimulation in 4 out of 6 dogs in model group and in none of the dogs in control group. Atrial myocardial collagen volume fraction was significantly increased in model group compared with the control group (P < 0.05). Ultrastructure examination in atrial tissue evidenced disorder, fracture, collagen fiber proliferation, mitochondrial swelling, blurred cristae, and intercalated disc distortion, expansion, part of gap junction disappears in model group. The serum levels of procollagen type III N-terminal peptide and type IV collagen in model group were significantly higher than in the control group (P < 0.05). The protein expression of Cx 40 in atrial myocardium in model group was significantly higher than in control group (P < 0.05), while Cx 45 protein expression was similar between two groups (P > 0.05). The left atrial CVF was positively correlated with Cx 40 (r = 0.671, P < 0.01).

CONCLUSIONIncreased myocardial fibrosis is positively correlated with upregulation of myocardial Cx 40 protein expression in left atrium in rapid atrial paced canine.

Animals ; Atrial Fibrillation ; metabolism ; pathology ; Cardiac Pacing, Artificial ; Connexins ; metabolism ; Disease Models, Animal ; Dogs ; Fibrosis ; Heart Atria ; Myocardium ; metabolism ; pathology

OBJECTIVESTo investigate the relationship of the transforming growth factor beta1 (TGF-β1) mRNA expression in atrial myocardium and the effectiveness of radiofrequency Maze procedure in patients with rheumatic valvular disease (RHD) and permanent atrial fibrillation (AF).

METHODSBetween January 2008 and September 2008, 40 patients with RHD and AF underwent a radiofrequency Maze procedure with concomitant valvular surgery. The patients were assigned to normal sinus rhythm (SR) group (group A) and persistence AF group (group B) according to the results of the 6-month follow-up. Another 10 patients with SR and RHD undergone valvular surgery alone were assigned to control group (group C). Left atrial appendage were obtained in all patients. Expressions of TGF-β1 mRNA were detected by semiquantitative RT-PCR technique. CVF-I and CVF-III were observed by sirius red staining.

RESULTSAt 6-month follow-up, there were 28 patients in group A and 12 in group B. Patients in group A and group B had higher mRNA expressions of TGF-β1, CVF-I and CVF-I/CVF-III compared with group C (P < 0.05). Also, the group B had higher mRNA expressions of TGF-β1, CVF-I and CVF-I/CVF-III than group A (P < 0.05). The patients who had return of functional atrial contraction in group A had lower mRNA expression than the non-return patients (39 ± 12 vs. 60 ± 12, P < 0.05). The TGF-β1 mRNA expression had a correlation with both the contents of CVF-I and left atrial diameter (r = 0.786, P < 0.05; r = 0.858, P < 0.05). Multiple logistic regression analysis revealed that the risk factors which independently associated with the postoperative persistence of atrial fibrillation at 6-month follow-up includes mRNA expression levels of TGF-β1 (OR = 1.13, 95%CI 1.05 - 1.18, P = 0.031), CVF-I (OR = 1.07, 95%CI 1.00 - 1.13, P = 0.037) and lett atrial diameter (OR = 2.23, 95%CI 1.08 - 4.59, P = 0.042).

CONCLUSIONSThe atrial TGF-β1 mRNA expression level could predict the persistence of AF and the return of the functional atrial contraction at 6-month follow-up in patients who underwent rheumatic valvular surgery and concomitant radiofrequency Maze procedure.

Atrial Fibrillation ; etiology ; metabolism ; surgery ; Catheter Ablation ; Follow-Up Studies ; Heart Atria ; metabolism ; Humans ; Rheumatic Heart Disease ; complications ; Transforming Growth Factor beta1 ; metabolism ; Treatment Outcome

The purpose of this study was to investigate the different effects of ACh on the action potential and force contraction in guinea pig atrial and ventricular myocardium by using standard microelectrodes and force transducer. The results showed that the duration of the action potential (APD) of atrial myocardium was shortened from 208.57+/-36.05 to 101.78+/-14.41 ms (n=6, P<0.01), and the APD of the ventricular myocardium was shortened from 286.73+/-36.11 to 265.16+/-30.06 ms (n=6, P<0.01).The amplitude of the action potential (APA) of the atrial myocardium was decreased from 88.00+/-9.35 to 62.62+/-20.50 mV (n=6, P<0.01), while the APA of the ventricular myocardium did not change significantly.The force contraction of atrial myocardium was inhibited completely (n=6, P<0.01), while the force contraction of ventricular myocardium was inhibited by 37.57+/-2.58% (n=6, P<0.01). The ACh effects correlated with its concentration. The K(D) of the APD shortening effects in the atrial and ventricular myocardium were 0.275 and 0.575 micromol/L. The K(D) of the negative inotropic in the atrial and ventricular myocardium were 0.135 and 0.676 micromol/L, respectively. The corresponding data points were compared using t test between the atrial and ventricular myocardium, and the differences were significant when the ACh concentration was above 10 nmol/L. Furthermore, atropine (10 micromol/L) and CsCl (20 mmol/L) blocked the effects of 10 micromol/L ACh on the APD of ventricular myocardium, while CdCl2 (0.1 mmol/L) had no influence on these effects. In conclusion, ACh could shorten the action potential duration and inhibit the force contraction of atrial and ventricular myocardium in a concentration-dependent manner. There are differences in the effects of ACh on the atrial and ventricular myocardium. The atrial myocardium is more sensitive to ACh than the ventricular myocardium. It is probable that the muscarinic receptor and the potassium channel, but not the calcium channel, are involved in the ACh-induced shortening of the ventricular APD.
Acetylcholine ; pharmacology ; Action Potentials ; drug effects ; Animals ; Calcium Channels ; metabolism ; Guinea Pigs ; Heart Atria ; drug effects ; Heart Ventricles ; drug effects ; Microelectrodes ; Potassium Channels ; metabolism ; Receptors, Muscarinic ; metabolism

Adolescent ; Diagnosis, Differential ; Echocardiography ; Female ; Heart Atria ; diagnostic imaging ; Heart Neoplasms ; diagnosis ; metabolism ; surgery ; Humans ; Immunohistochemistry ; Myxoma ; diagnosis ; metabolism ; surgery ; Sarcoma ; diagnosis ; metabolism ; surgery ; Vimentin ; analysis

OBJECTIVETo observe the collagen spatial distribution, collagen volume fraction (CVF) and Cx40, Cx43mRNA expressions in rapid atrial pacing dogs post vagal denervation by removing fat pad located between the medial superior vena cava and aortic root (SVC-Ao fat pad).

METHODSTwenty-four dogs were randomly divided into unpaced sham operation group (S group, n = 8), Keeping SVC-Ao fat pad group (K group, n = 8) and Removing SVC-Ao fat pad group (R group, SVC-Ao fat pad was removed by surgical excision before pacing, n = 8). K and R groups were paced for six weeks. Six weeks later, all dogs were sacrificed, left atrium (LA), right atrium (RA), left atrial appendage (LAA), right atrial appendage (RAA) and atrial septum (AS) were collected and stained with HE or Masson Trichrome or frozen in liquid nitrogen for quantifying the expression of Cx40, Cx43 mRNA by Real-time quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR).

RESULTSSpatial distribution of collagen fibers as well as CVF between S and R group were similar (all P > 0.05). CVF was significantly higher in K group compared to R group, especially at LAA and AS locations (all P < 0.05). Cx40mRNA expression in K group was significantly decreased in LA, RA, and significantly increased in LAA, RAA and AS compared those in S group (all P < 0.05), significantly lower in LA and RA while significantly higher in LAA and RAA compared to R group (all P < 0.05). Cx43mRNA expression in K group was significantly reduced in LA, RA, LAA and RAA while significantly increased in AS compared to S group (all P < 0.05), significantly higher in LA, RA, RAA and AS while significantly lower in LAA compared to R group.

CONCLUSIONPacing induced collagen remodeling and modulation on Cx40mRNA and Cx43 mRNA expressions could be partially attenuated by removing SVC-Ao fat pad suggesting vagal denervation plays a key role in the initiation and preservation of atrial fibrillation.

Animals ; Atrial Fibrillation ; metabolism ; pathology ; Cardiac Pacing, Artificial ; Collagen ; metabolism ; Connexin 43 ; metabolism ; Connexins ; metabolism ; Dogs ; Heart Atria ; metabolism ; pathology ; RNA, Messenger ; genetics

OBJECTIVESK channels are existed in hearts of mouse, rat, and human. Biochemical evidence indicates that SK2 channels are expressed more in atrial than in ventricular tissue. SK channels are highly sensitive to the calcium concentration of the pipette solution. In the present study, performed whole-cell patch clamp was used to detect the calcium sensitivity of small conductance Ca(2+)-activated K+ channels (SK) currents between sinus ryhthm (SR) and auricular fibrillation (AF).

METHODSThe patients who accepted cardiopulmonary bypass were divided into two groups: 21 patients with SR and 8 patients with AF. The enzymatic dissociation method was improved according to the previous research by our lab. The performed whole cell patch-clamp technique was used to record SK2 currents in both SR and AF groups at room temperature.

RESULTSThe SK2 current density was (-2.92 +/- 0.35) pA/pF in SR group (n = 6) vs (-6.83 +/- 0.19) pA/pF in AF group at -130 mV (n = 3, P < 0.05). In SR group, the SK2 current densities in calcium concentration of the pipette solution are (-1.43 +/- 0.33) pA/pF (n = 7), (-2.92 +/- 0.35) pA/pF (n = 6), (-10.11 +/- 2.15) pA/pF (n = 8, P < 0.05); In AF group, the SK2 current densities are (-2.17 +/- 0.40) pA/pF (n = 4), (-6.83 +/- 0.19) pA/pF (n = 3), (-14.47 +/- 2.89 pA/pF) (n = 4, P < 0.05).

CONCLUSIONThe SK2 currents recorded in this experiment are voltage-independent, inwardly rectifying and apamin-sensitive. When the calcium concentration of the pipette solution is 5 x 10(-7) mol/L, SK2 current density in AF group are significantly larger than those in SR group. It suggests that SK currents involve the cardiomyocytes electric remodeling in AF. In AF group, the SK2 currents are more sensitive to free calcium ion. It shows that the increased sensitivity of SK2 currents to the calcium contribute to the occurrence and maintenance of AF.

Atrial Fibrillation ; metabolism ; physiopathology ; Calcium ; metabolism ; Cells, Cultured ; Heart Atria ; metabolism ; Humans ; Membrane Potentials ; physiology ; Myocytes, Cardiac ; metabolism ; Patch-Clamp Techniques ; Potassium Channels, Calcium-Activated ; physiology

OBJECTIVETo investigate rapid atrial pacing (RAP) induced atrial ultrastructural changes and mRNA and protein expression changes of L-type calcium channel subunits and potassium channel Kv4.3 in a rabbit model.

METHODSThirty-six rabbits were electrically paced at a frequency of 600 beats/min for durations ranging from 0 - 48 h via bipolar endocardial leads through surgical techniques. Ultrastructural changes of the atrium were observed through a transmission electron microscope (TEM), L-type calcium channel subunits and potassium channel Kv4.3 expressions at mRNA and protein levels were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot.

RESULTSAtrial ultrastructure changes characterized by mitochondrial vacuolization, myofilament lysis, and glycogen accumulation were detected obvious at 3 h post pacing. Down-regulated mRNA expression of Ca(2+) channel beta1 and alpha1 subunits was observed 6 h post pacing, Kv4.3 mRNA down-regulation occurred 24 h post pacing, auxiliary subunit alpha2 was not affected by pacing. Protein expression of alpha1c subunit and potassium channel Kv4.3 paralleled their mRNA expression changes.

CONCLUSIONRAP induced ultrastructural changes of the atrium and down-regulated mRNA and protein expressions of L-type calcium channel subunits and potassium channel Kv4.3 occurred thereafter in response to intracellular calcium overload induced by RAP.

Animals ; Calcium Channels, L-Type ; genetics ; metabolism ; Cardiac Pacing, Artificial ; methods ; Female ; Heart Atria ; metabolism ; ultrastructure ; Male ; Patch-Clamp Techniques ; Potassium Channels ; genetics ; metabolism ; RNA, Messenger ; metabolism ; Rabbits

OBJECTIVETo study the relation of the structural remodeling processes and activation of calpain I.

METHODSFifteen dogs were randomly divided into three groups. The dogs in pacing group (n=5) and inhibitor group (n=5) were subjected to 3 weeks of rapid atrial pacing at 600 beats/min, control dogs (n=5) were in sham-operated group. The dogs in inhibitor group were administered intravenous N-Acetyl-Leu-Leu-Met (ALLM), a calpain inhibitor, and in pacing group and sham-operated group were administered intravenous DMSO. The activity of calpain I was measured by hydrolyzing Suc-Leu-Leu-Val-Tyr-7-amino-4-methyl-coumarin. The ultrastructure of atrium was examined by light and electron microscopy. TnT expression was assessed by Western blot. Echocardiography examination was performed in all the three groups.

RESULTSCalpain I activity was significantly increased in pacing group (2.3-fold, P<0.01), and decreased in inhibitor group (1.1-fold, P>0.05), compared to sham-operated group respectively. The percentages of myolysis were (76.7 +/- 5.9)% and (20.8 +/- 8.1)% in pacing group and inhibitor group respectively (P<0.01). TnT expression decreased in the rapid pacing-induced persistent atrial fibrillation, and these effects were inhibited by calpain I inhibitor ALLM. The area and volume of left atrium tended to increase after 3 weeks ALLM treatment in inhibitor group, but the change was not as prominent as in pacing group (P<0.05).

CONCLUSIONSALLM can decrease calpain I activity, and prevent canine atrial cardiomyocyte structural remodeling during atrial fibrillation. This study provided a capacity of atrial cardiomyocyte protection.

Animals ; Atrial Fibrillation ; metabolism ; physiopathology ; Atrial Function, Left ; Calpain ; antagonists & inhibitors ; metabolism ; Cardiac Pacing, Artificial ; Disease Models, Animal ; Dogs ; Heart Atria ; ultrastructure ; Myocardium ; metabolism ; Troponin T ; metabolism

OBJECTIVEThe aim of the present study was to detect the expression of calpain-I, calpastatin, caspase-3 and apoptosis in the left atria of patients with rheumatic heart disease (RHD), and to find the association of these factors. Also, it was intended to investigate the effect of the above factors on the mechanism of atrial fibrillation (AF).

METHODS43 patients with RHD undergoing valve-replacement were included, 15 patients with regular sinus rhythm (Group RSR), 8 patients with paroxysmal AF (Group AF1) and 20 patients with permanent AF (Group AF2). Western blot was used to examine the content of calpain-I, caspase-3 and calpastatin. The apoptosis index (AI) was measured by TUNEL.

RESULTS(1) Expression of calpain-I in group AF2 was increased to (344.0 +/- 101.9)%, and caspase-3 was increased to (394.0 +/- 99.4)% compared to group RSR (P < 0.01, respectively). Amount of calpastatin was reduced to (27.0 +/- 12.8)% (P < 0.01). The expressions of these proteins were unchanged in group AF1. (2) AI in group AF2 was higher than that in groups RSR and AF1 (P < 0.01). (3) In group AF2, the levels of calpain-I, caspase-3 and AI were positively relative to left atrial dimension and AF duration, P < 0.05 - 0.01, respectively, whereas calpastatin was negatively correlated with left atrial dimension and AF duration (P = 0.007 and P = 0.001, respectively). (4) The protein content of calpain-I was positively related with that of caspase-3 and AI (P < 0.01, respectively), and the content of calpastatin was negatively related with that of calpain-I and caspase-3 (P < 0.01, respectively).

CONCLUSIONSApoptosis of atrial cell increased in left atria and the protein contents of calpain-I, caspase-3 and calpastatin significantly altered during AF in humans with RHD. The observed interactions suggest that these factors compose a system to cause the structural remodeling and dysfunction of atria. The course may play a key role in promoting the onset and maintenance of AF.

Adult ; Apoptosis ; Atrial Fibrillation ; etiology ; metabolism ; Atrial Function ; Calcium-Binding Proteins ; metabolism ; Calpain ; metabolism ; Caspase 3 ; metabolism ; Female ; Heart Atria ; metabolism ; Humans ; Male ; Middle Aged ; Myocytes, Cardiac ; metabolism ; Rheumatic Heart Disease ; complications ; metabolism