Animals ; Heart Ventricles ; cytology ; Lipid Bilayers ; Potassium Channels ; Sarcolemma ; physiology ; Swine

Cellular excitability is an important physiological factor in maintaining normal cardiac activity. The present study was designed to investigate the ionic mechanism underlying different excitability in atrial and ventricular myocytes of guinea pig heart using a whole-cell patch configuration. We found that excitability is lower in ventricular myocytes than that in atrial myocytes. Although the density of voltage-gated fast Na(+) current (INa) was lower in ventricular myocytes, it would not correlate to the lower excitability since its availability was greater than that in atrial myocytes around threshold potential. Classical inward rectifier K(+) current (IK1) was greater in ventricular myocytes than that in atrial myocytes, which might contribute in part to the lower excitability. In addition, the transient outward K(+) current with inward rectification (Itoir) elicited by depolarization was greater in ventricular myocytes than that in atrial myocytes and might contribute to the lower excitability. In ventricular myocytes, Ba(2+) at 5 µmol/L significantly inhibited Itoir, enhanced excitability, and shifted the threshold potential of INa activation to more negative, and the effect was independent of affecting INa. Our results demonstrate the novel information that in addition to classical IK1, Itoir plays a major role in determining the distinctive excitability in guinea pig atrial and ventricular myocytes and maintaining cardiac excitability. More effort is required to investigate whether increase of Itoir would be protective via reducing excitability.
Animals ; Atrial Function ; Guinea Pigs ; Heart Atria ; cytology ; Heart Ventricles ; cytology ; Myocytes, Cardiac ; physiology ; Potassium Channels, Inwardly Rectifying ; physiology ; Ventricular Function ; Voltage-Gated Sodium Channels ; physiology

Computer simulation is one of the powerful protocols to study electrophysiology theoretically. In this paper,the algorithm of Rush and Larsen was used to solve the ordinary differential equations (ODE's) in the Luo-Rudy models of mammalian ventricular cell. The operator splitting and adaptive time step methods were used to solve the partial differential equations (PDE's) in cardiac tissue conduction models. Using these methods we accomplished the simulation programs of single ventricular cell model and two-dimensional (2-D) tissue model. The methods of initiating spiral waves were studied with this software. The data obtained from 2-D simulation can be used for further study on isopotential contour lines, spiral wave tip trajectories, and pseudo-ECG.
Algorithms ; Computer Simulation ; Electrocardiography ; Electrophysiology ; Heart Ventricles ; cytology ; Humans ; Models, Cardiovascular ; Myocytes, Cardiac ; physiology ; Software ; Ventricular Function

AIMTo observe the effects of adenosine on intracellular calcium concentration ([Ca2+]i) level in guinea pig ventricular myocytes and to define the possible mechanisms involved.

METHODSThe effects of adenosine on [Ca2+]i were investigated in guinea pig ventricular myocytes. [Ca2+]i was detected by laser confocal microscopy and represented by relative fluorescent intensity ((FI-FI0)/FI0, %, FIo: control, FI: administration of drugs).

RESULTS(1) Adenosine (10, 50, 100 micromol/L) reduced [Ca2+]i of ventricular myocytes in both normal Tyrode's solution and Ca(2+) -free Tyrode's solution in a concentration-dependent manner. (2) Tyrode's solution containing 30 mmol/L KCl (high K+ Tyrode's solution) induced [Ca2+]i elevation in ventricular myocytes, while adenosine (10, 50, 100 micromol/L) markedly inhibited the increase in [Ca2+]i induced by KCl. (3) Pretreatment with DPCPX (1 micromol/L) significantly reduced the effects of adenosine (100 micromol/L) in high K+ Tyrode's solution. The effects of adenosine (100 micromol/L) on [Ca2+]i in high K+ Tyrode's solution were also partially attenuated by pretreatment with L-NAME (1 mmol/L). (4) Adenosine (100 micromol/L) markedly inhibited the low concentration of ryanodine-induced [Ca2+]i increase in Ca(2+) -free Tyrode's solution. (5) When the propagating waves of elevated [Ca2+]i (Ca2+ waves) were produced by increasing extracellular Ca2+ concentration from 1 mmol/L to 10 mmol/L, adenosine (100 micromol/L) could block the propagating waves of elevated [Ca2+]i, reduce the frequency and duration of propagating waves, and reduce [Ca2+]i as well.

CONCLUSIONAdenosine may reduce the [Ca2+]i in isolated guinea pig ventricular myocytes via inhibiting Ca2+ influx and alleviating Ca2+ release from sarcoplasmic reticulum(SR). The reduction of Ca2+ influx might be due to the inhibition of voltage-dependent Ca2+ channel via adenosine A1 receptor, and NO might be involved in this process.

Adenosine ; pharmacology ; Animals ; Calcium ; metabolism ; Cells, Cultured ; Guinea Pigs ; Heart Ventricles ; cytology ; Myocytes, Cardiac ; drug effects ; metabolism

Cardiac extracellular matrix (ECM), generated from the process of decellularization, has been widely considered as an ideal source of biological scaffolds. However, current ECM preparations are generally difficult to be applied to generate cardiac tissue. Our research was aimed to improve decellularization protocols to prepare cardiac ECM slices. Adult murine ventricular tissues were embedded in low melting agarose and cut into 300 μm slices, and then were divided randomly into three groups: normal cardiac tissue, SDS treated group (0.1% SDS) and SDS+Triton X-100 treated group (0.1% SDS+0.5% Triton X-100). Total RNA content and protein content quantification, HE staining and immunostaining were used to evaluate the removal of cell components and preservation of vital ECM components. Furthermore, murine embryonic stem cell-derived cardiomyocytes (mES-CMs) and mouse embryonic fibroblasts (MEFs) were co-cultured with ECM slices to evaluate biocompatibility. The relative residual RNA and protein contents of ECM slices significantly decreased after decellularization. HE staining showed that SDS+Triton X-100 treatment better destroyed cellular structure and removed nuclei of ECM slices, compared with SDS treatment. Immunostaining showed that collagen IV and laminin were better preserved and presented better similarity to original cardiac tissue in ECM slices acquired by SDS+Triton X-100 treatment. However, collagen IV and laminin were significantly decreased and arranged disorderly in SDS treated group. We observed effective survival (≥ 12 days) of MEFs and mES-CMs on ECM slices acquired by SDS+Triton X-100 treatment, and signs of integration, whereas those signs were not found in SDS treated group. We concluded that, compared with traditional SDS method, new combined protocol (SDS+Triton X-100) generated ECM slices with better component and structural preservation, as well as better biocompatibility.
Animals ; Extracellular Matrix ; chemistry ; Heart Ventricles ; cytology ; Mice ; Octoxynol ; Sodium Dodecyl Sulfate ; Tissue Engineering ; methods ; Tissue Scaffolds

AIMTo observe the effects of stress on Ica-L, steady-state activation curves and steady-state inactivation curves.

METHODSUse NE to construct stress cell model, then the whole-cell patch-clamp recording technique was used to record the Ica-L, the steady-state activation curves and the steady-state inactivation curves. With FCM technique, we observed the rate of apoptosis of cardiomyocytes. By dying cells with Fura-2 and fluorometry, we determined [Ca2+]i.

RESULTSThe amplitude of peak current of Ica-L increased significantly, and by analyzing the steady-state activation curve, we found that the curve was shifted to left, the V1/2 of stress group was (-14.59 +/- 0.24 ) mV vs (-0.69 +/- 0.36) mV of control group. The rate of apoptosis was increased from 0.36% to 2.17% (P < 0.01). The [Ca2+]i increased by 16.7%.

CONCLUSIONStress can bring on increasing of Ica-L, and the channels are easy to be activated. These changes can cause "calcium overload" and then induce apoptosis which lead to injury of myocytes in stress.

Animals ; Apoptosis ; Calcium Channels, L-Type ; metabolism ; Cells, Cultured ; Heart Ventricles ; cytology ; Male ; Myocytes, Cardiac ; cytology ; metabolism ; Patch-Clamp Techniques ; Rats ; Rats, Wistar ; Stress, Physiological

The present study was to investigate the effects of agmatine (Agm) on free intracellular calcium concentration ([Ca(2+)]( i )) of isolated rat ventricular myocytes. [Ca(2+)]( i ) was measured by confocal microscopy in single rat ventricular myocytes which were dissociated by enzymatic dissociation method and loaded with Fluo 3-AM. The changes in [Ca(2+)]( i ) were represented by fluorescence intensity (FI) or relative fluorescence intensity (F/F(0)%). The results showed that the control level of FI value of single rat ventricular myocytes was 128.8+/-13.8 and 119.6+/-13.6 in the presence of normal Tyrode's solution containing Ca(2+) 1.0 mmol/L and Ca(2+)-free Tyrode's solution, respectively. There was no difference between these two groups (P>0.05). Agm 0.1, 1, and 10 mmol/L significantly reduced the [Ca(2+)]( i ) in both extracellular solutions in a concentration-dependent manner. The similar effect of Agm on [Ca(2+)]( i ) was also observed in the presence of EGTA 3 mmol/L. KCl 60 mmol/L, PE 30 micromol/L, and Bay-K-8644 10 micromol/L, all these substances induced [Ca(2+)]( i ) elevations in ventricular myocytes. Agm (0.1, 1, and 10 mmol/L) markedly inhibited the increase in [Ca(2+)]( i ) induced by KCl, phenylephrine (PE), and Bay-K-8644. When Ca(2+) waves were produced by increasing extracellular Ca(2+) concentration from 1 to 10 mmol/L, 1 mmol/L Agm could block the propagating waves of elevated [Ca(2+)]( i ), and reduce the velocity and duration of propagating waves. These results suggest that Agm possesses an inhibitory effects on [Ca(2+)]( i ) via blocking voltage-dependent Ca(2+) channel, and possibly by alleviating calcium release from SR in single isolated rat ventricular myocytes.
Agmatine ; pharmacology ; Animals ; Calcium ; metabolism ; Calcium Channels ; drug effects ; Cells, Cultured ; Female ; Heart Ventricles ; cytology ; Male ; Myocytes, Cardiac ; cytology ; drug effects ; metabolism ; Rats ; Rats, Sprague-Dawley

The effects of low concentration of dihydroouabain (DHO) on intracellular calcium concentration ([Ca(2+)](i)) were investigated in guinea pig ventricular myocytes. [Ca(2+)](i) was detected by confocal microscopy and represented by fluorescent intensity. DHO (1 fmol/L~1 mmol/L) increased [Ca(2+)](i), especially at 10 pmol/L. Nisoldipine, egtazic acid, or tetrodotoxin partially inhibited the effect of 10 pmol/L DHO on [Ca(2+)](i). The effects of DHO remained in the absence of extracellular K(+) and Na(+). These results suggest that low concentration of DHO might increase [Ca(2+)](i) via the receptor-operated Ca(2+) channels, TTX-sensitive Na(+) channels or/and triggering of intracellular calcium release; Na(+)/K(+) pump and Na(+)/Ca(2+) exchange seem not involved in the effect of DHO.
Animals ; Calcium ; metabolism ; Guinea Pigs ; Heart Ventricles ; cytology ; Male ; Myocytes, Cardiac ; cytology ; drug effects ; metabolism ; Ouabain ; analogs & derivatives ; pharmacology ; Patch-Clamp Techniques

Using whole cell patch clamp, the effects of angiotensin II (Ang II) on the current L-type calcium channel (I(Ca.L)) were observed in guinea pig isolated ventricular myocytes under simulated ischemia condition, which was realized through hypoxia, glucose deficiency, high lactic acid and acidosis. The results showed that, under the condition of simulated ischemia, the peak of I(Ca.L) was reduced with maximal activation potential at 0 mV. Administration of Ang II (100 nmol/L) enhanced the peak of I(Ca.L) during ischemia and shifted the maximal activation potential to -10 mV. The possible mechanism of these effects is discussed.
Angiotensin II ; pharmacology ; Animals ; Calcium Channels, L-Type ; drug effects ; Cells, Cultured ; Guinea Pigs ; Heart Ventricles ; cytology ; Myocytes, Cardiac ; cytology ; drug effects ; Patch-Clamp Techniques

Experiments were performed to investigate the heterogeneity of the action potential and ion currents in left ventricular myocytes of the rabbit. Myocytes were isolated by enzymatic method. The sub-endocardial (Endo) and sub-epicardium (Epi) tissues were separated from the other region (midmyocardium, M) with a razor. Single cells in each region were obtained by gentle shaking and dispersing in a chamber filled with normal Tyrode's solution. The results showed that the action potential and the ion currents in the three layers were significantly different. M cells had a more pronounced spike-and-dome configuration, with a significantly larger phase 1 magnitude and plateau voltage. Action potential duration (APD) in M cells was longer than that in Epi or Endo cells. I(Ca, L) and I(to) in M cells were higher than those of Epi and Endo. On the contrary, I(K,s) in M cells was the minimum compared with those in the three LV walls. The differences in ion currents may well explain the heterogeneity of action potentials in M layers of the rabbit heart.
Action Potentials ; physiology ; Animals ; Calcium Channels ; physiology ; Female ; Heart Ventricles ; cytology ; Male ; Myocytes, Cardiac ; cytology ; metabolism ; physiology ; Patch-Clamp Techniques ; Potassium Channels ; physiology ; Rabbits