Declining trend in the in-hospital case-fatality rate from acute myocardial infarction in Miyagi Prefecture from 1980 to 1999.

The case-fatality rate from acute myocardial infarction (AMI) appears to have been declining in recent decades, so the present study reviewed the trend in in-hospital case-fatalities from AMI in Miyagi Prefecture, Japan, 1980-1999. The causes of death and the effects of gender and age on the trend were also analyzed. From the AMI registration database of the Miyagi Study Group for AMI, 12,961 cases of AMI were analyzed. The 30-day in-hospital case-fatality was calculated from the data for 1980-1999: data for causes of death were available for 1980-1997, and the data concerning primary percutaneous transluminal coronary angioplasty (PTCA) for AMI were available for 1997-1999. The in-hospital case-fatality rate declined from 17.0% in the early 80s to 7.3% in the late 90s (approximately 57% reduction). The in-hospital case-fatality rate was higher in female patients. Rhythm failure substantially decreased in the late 1980s. Pump failure is decreasing, but is still the biggest problem. The in-hospital case-fatality rate was significantly lower in patients received PTCA. The declining trend in the in-hospital case-fatality rate suggests the benefits of current therapeutic procedures, including primary PTCA, for AMI. Pump failure is an important target for further decreasing the trend.

[18F] labeled diacylglycerol analogue as a potential agent to trace myocardial phosphoinositide metabolism.

Phosphoinositide metabolism plays an important role in cardiac pathophysiology. To investigate whether [18F]diacylglycerol could be used to trace myocardial phosphoinositide metabolism, lipids were extracted from rat myocardium after the injection. 1-[8-[18F]fluorooctanoyl]-2-palmitoylglycerol and 1-[8-[18F]fluoropalmitoyl]-2-palmitoylglycerol were predominantly metabolized to phosphatidylethanolamine and triacylglycerol, respectively. The radioactivity incorporated into phosphoinositide metabolism was 51, 44, 32, and 30% 3, 5, 10, and 30 minutes after the injection of 1-[4-[18F]fluorobutyryl]-2-palmitoylglycerol, respectively. 1-[4-[18F]fluorobutyryl]-2-palmitoylglycerol might be a potential tracer to evaluate myocardial phosphoinositide metabolism early after the injection.

Interaction between sarcomere and mitochondrial length in normoxic and hypoxic rat ventricular papillary muscles.

We hypothesized that the mitochondrial length may be altered according to changes in the sarcomere length, and that this relationship may be affected by exposure to hypoxia. Rat ventricular papillary muscles were isolated and immersed in normoxic or hypoxic solutions for 10 min. Sarcomeres of various lengths were obtained by fixing the papillary muscles in a slack or stretched state, or after exposure to a contracture solution containing saponin and CaCl(2). The mitochondrial length measured using electron microscopy significantly correlated to the length of the adjacent sarcomere in both the normoxic (n=767) and hypoxic (n=1145) groups (P<.0001). The slope of the regression line, however, was significantly less steep, and its intercept was significantly larger in the hypoxic group than in the normoxic group (analysis of covariance). When we analyzed the mitochondrial lengths among the three sarcomere-length subgroups (<1.5, 1.5-2.0, and >2.0 microm), the mitochondrial length was significantly shorter in the hypoxic condition than in the normoxic condition at sarcomere lengths greater than 2.0 microm. Staining for desmin, the major muscle-type intermediate filament, the longitudinal system of which connects the mitochondria with the Z bands of sarcomeres, showed a clear cross-striation pattern in both papillary muscles with and without the exposure to hypoxia, suggesting that desmin was preserved after the exposure to hypoxia. These data indicate that the mitochondrial length changes according to changes in the sarcomere length, suggesting the possible role of mitochondria as an internal load against myocyte contraction. It is also suggested that mitochondria exposed to hypoxia may be more resistive to both compression and stretch in a longitudinal direction than those in the normoxic condition.

Long-term right ventricular volume overload increases myocardial fluorodeoxyglucose uptake in the interventricular septum in patients with atrial septal defect.

BACKGROUND: Several studies have shown that long-term right ventricular (RV) overload in animal models alters myocardial energy substrate metabolism. However, whether long-term RV volume overload alters this metabolism in the human is unclear. METHODS AND RESULTS: We performed positron emission tomography with [(18)F]fluorodeoxyglucose (FDG) and single-photon emission tomography (SPECT) with [(201)Tl]TlCl (Tl) and [(123)I]15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) in 11 patients with atrial septal defect (ASD) and 11 control subjects. In the FDG study, we calculated myocardial metabolic rate of glucose (MMR) in interventricular septum (IVS) and left ventricular (LV) free wall. MMR was significantly increased in IVS compared with LV free wall in the ASD patients (420+/-35 versus 333+/-32 mol x kg(-1) x min(-1); P<0.05) but not in the control group (347+/-27 versus 357+/-25 mol x kg(-1) x min(-1)). In both ASD and control groups, SPECT count was not significantly different between IVS and LV free wall in Tl (ASD, 160+/-11 versus 177+/-12; control, 141+/-12 versus 157+/-14 counts per 15 minutes) and BMIPP studies (ASD, 203+/-14 versus 212+/-18; control, 162+/-16 versus 176+/-16 counts per 15 minutes). MMR in the IVS/LV free wall ratio in the ASD group significantly correlated with indices related to RV volume overload. CONCLUSIONS: Given the assumption that long-term RV volume overload did not affect the lumped constant, the present study suggests that, unlike myocardial perfusion or fatty acid analogue uptake, myocardial glucose utilization in IVS relative to LV free wall is increased in relation to long-term RV volume overload in patients with ASD.

Diacylglycerol delays pH(i) overshoot after reperfusion and attenuates contracture in isolated, paced myocytes.

Although protein kinase C (PKC) plays a pivotal role in ischemic preconditioning, it is not clear what the end effector is that protects the myocardium. In isolated, paced (1.25 Hz, 36-37 degrees C) adult rat cardiomyocytes, the effects of PKC preactivation by diacylglycerol on cell motion, intracellular Ca(2+) concentration ([Ca(2+)](i); indo 1), and intracellular pH (pH(i); seminaphthorhodafluor-1) during simulated ischemia-reperfusion (I/R) were investigated. The degree of reperfusion-induced contracture was significantly attenuated in the myocytes pretreated with 10 microM 1, 2-dioctanoyl-sn-glycerol (DOG; n = 19) compared with the untreated myocytes (n = 23, P < 0.02). There were no differences in twitch amplitude, end-diastolic [Ca(2+)](i), or peak-systolic [Ca(2+)](i) during I/R between the DOG-pretreated and untreated myocytes. Although there were no differences in pH(i) during ischemia, the pH(i) overshoot during reperfusion was significantly delayed in the DOG-pretreated myocytes compared with the untreated myocytes (n = 17 for each, P < 0.01). Chelerythrine completely abolished the favorable effects of DOG on the reperfusion-induced contracture and the pH(i) overshoot. These data suggest that diacylglycerol attenuates I/R injury in isolated, paced cardiomyocytes, which may be related to the slower pH(i) overshoot during reperfusion.

Heterogeneous fatty acid uptake early after reperfusion in rat hearts.

We determined whether spatial distributions of substrate uptake are heterogeneous within the area at risk during reperfusion. Quantitative autoradiography with imaging plates and two long-lived radioisotopes was applied to 15 open-chest, anesthetized rats subjected to 30 min of coronary artery ligation and 30 min of reperfusion. Regions showing increased beta-methyl-[1-14C]heptadecanoic acid ([14C]BMHDA) uptake (166 +/- 17% of that in the nonischemic area) appeared at the lateral borders and subepicardial layer within the area at risk, and 2-deoxy-D-[1-3H]glucose ([3H]DG) uptake was 103 +/- 24% in these regions. Regions with decreased [14C]BMHDA uptake (28 +/- 11%) occupied the midmyocardial layer except at the lateral borders within the area at risk, and [3H]DG uptake was 62 +/- 18% in these regions. The percentage interregional coefficients of variation (index of heterogeneity) in [14C]BMHDA uptake, [3H]DG uptake, and blood flow were higher in the area at risk than in the nonischemic area (76 +/- 23 vs. 21 +/- 7%, 39 +/- 10 vs. 21 +/- 7%, and 49 +/- 19 vs. 14 +/- 4%, respectively). Heterogeneous distributions of substrate uptake may explain the conflicting results concerning substrate metabolism during reperfusion.

Effect of dantrolene sodium on calcium-overloaded heart.

Spontaneous asynchronous contractile activity caused by spontaneous release of calcium ions (Ca2+) from the sarcoplasmic reticulum (SR) is thought to be the cause of deterioration of ventricular function under conditions of calcium overload. We examined whether dantrolene sodium, which can inhibit Ca2+ release from the skeletal SR, improves the systolic and diastolic function of calcium-overloaded hearts. In isolated hamster left ventricles, the concentration of Ca2+ in the perfusate ([Ca2+]o) was increased from 1 mmol/L to 7 mmol/L in 1-mmol/L steps in the absence (control, n = 6) and presence of dantrolene sodium (11.8 mumol/L, n = 5). Left ventricular developed pressure and its maximum rate of rise (max dP/dt) increased with an increase in [Ca2+]o up to 4 mmol/L, and decreased with a further increase in [Ca2+]o. In the presence of dantrolene sodium, developed pressure and max dP/dt increased up to 5 mmol/L [Ca2+]o. Thus, dantrolene sodium improves Ca2+ tolerance. In isolated ventricles perfused with 1 mmol/L [Ca2+]o, dantrolene sodium decreased developed pressure by 33.7 +/- 7.4% and max dP/dt by 37.4 +/- 5.6% (mean +/- SEM, n = 8) at 1 mmol/L [Ca2+]o. In contrast, at 5 mmol/L [Ca2+]o ('calcium-overloaded state'), dantrolene sodium increased developed pressure by 6.8 +/- 2.6% and max dP/dt by 14.4 +/- 5.7%, and decreased the end-diastolic pressure by 5.3 +/- 1.9% (n = 8). Dantrolene sodium partially suppressed the spontaneous contractile activities observed microscopically on the epicardium of ventricles perfused with 5 mmol/L [Ca2+]o. Dantrolene sodium improved the Ca2+ tolerance of left ventricles and exerted positive inotropic effects and decreased diastolic stiffness in calcium-overloaded hamster left ventricles by suppressing spontaneous contractile activity.

The rise time of the monophasic action potential--a new index of local use-dependent conductivity by sodium channel blockers in human myocardium.

The kinetics of global use-dependent conduction slowing produced by sodium channel blockers in the human heart, estimated as a change in the QRS width, are known to be similar to those of use-dependent block of the maximum rate of depolarization in in vitro studies. However, the kinetics of the regional use-dependent decrease in conductivity have not been investigated. We examined whether the rise time of the monophasic action potential would be clinically useful as a marker of the local use-dependent decrease in conductivity by sodium channel blockers. In 12 patients without organic heart disease, monophasic action potentials (MAPs) were recorded at the right ventricular endocardium using a contact electrode before and after the administration of disopyramide (n = 6, 2 mg/kg, i.v.) or pilsicainide (class Ic agents, n = 4, 1 mg/kg, i.v., and n = 2, 150 mg, po) while the stimulus frequency was abruptly increased from 100/min to 150/min. The rise time, defined as the interval from the pacing pulse to the first peak deflection of the monophasic action potential, and the ORS width were measured simultaneously. In the absence of the sodium channel blockers, the abrupt increase in heart rate did not alter the QRS width or the rise time. In the presence of the agents, both variables were lengthened exponentially. The rate constants of onset changes in the QRS width and the rise time were 2.1 +/- 0.5 beats and 2.1 +/- 0.4 beats after the administration of disopyramide, and 7.5 +/- 3.0 beats and 8.2 +/- 4.0 beats after pilsicainide, respectively. The rate constant of the rise time was closely correlated with that of the QRS width. The present results are very closely comparable with the onset rate constants of use-dependent block of the maximum rate of depolarization in in vitro studies. These results suggest that (1) the rise time is a good indicator of local use-dependent decrease in conductivity by sodium channel blockers in human hearts and (2) the local use-dependent decrease in conductivity has kinetics similar to those of use-dependent sodium channel blocks.

Stimulated glucose uptake in the ischemic border zone: its dependence on glucose uptake in the normally perfused area.

UNLABELLED: During acute regional myocardial ischemia, a "border zone" exists where the spatial distributions of blood flow and substrate uptake show gradual changes. We investigated the relationship between blood flow and glucose uptake in the border zone during acute regional ischemia. METHODS: Newly developed quantitative autoradiography using imaging plates and two long-lived radioisotopes was applied to rat hearts subjected to 30 min of left coronary artery occlusion. Blood flow, glucose uptake and fatty acid uptake was assessed with 4-[N-methyl-14C]iodoantipyrine, 2-deoxy-D-[1-3H]glucose (3H-DG) and beta-methyl[1-14C]heptadecanoic acid (14C-BMHDA), respectively. RESULTS: In rats showing 3H-DG uptake in the normally perfused area (Norm) of 254 +/- 96 Bq/mg (high-DG) and 56 +/- 20 Bq/mg (low-DG) (n = 4 for each), 3H-DG uptake in the border zone was 148 +/- 52 Bq/mg and 58 +/- 15 Bq/mg (p < 0.05 high- versus low-DG), respectively. The relationship between blood flow and 3H-DG uptake in the border zone was altered by the different 3H-DG uptake levels in Norm. In high-DG, 3H-DG uptake in the border zone was reduced significantly according to the decrease in the percentage of blood flow. However, in low-DG, no significant differences in 3H-DG uptake were found among the regions in the border zone with different levels of the percentage of blood flow, except in the region with 10%-19% of the percentage of blood flow. In the border zone, the percentage of 3H-DG uptake per unit blood flow normalized to that in Norm increased according to the decrease in the percentage of blood flow, and this increase was steeper in low-DG than in high-DG (p < 0.0005). The percentage of 14C-BMHDA uptake was lower than the percentage of 3H-DG uptake (27 +/- 3% versus 78 +/- 18% of that in Norm, p < 0.0005) in the peripheral ischemic area. CONCLUSION: The relationship between blood flow and glucose uptake in the ischemic border zone was altered by the different glucose uptake levels in Norm. Glucose uptake in the border zone was higher in rats with higher glucose uptake levels in Norm, suggesting that glucose uptake in the border zone stimulated by ischemia can be accelerated still more by humoral factors.

Myocardial glucose metabolism is different between hypertrophic cardiomyopathy and hypertensive heart disease associated with asymmetrical septal hypertrophy.

Myocardial glucose metabolism has been shown to be heterogeneous in patients with hypertrophic cardiomyopathy (HCM). We tested the hypothesis that myocardial glucose metabolism differs between patients with HCM and those with hypertensive heart disease (HHD) associated with asymmetrical septal hypertrophy. We studied 12 patients with HCM, 7 HHD patients associated with asymmetrical septal hypertrophy using 18F 2-deoxyglucose (FDG) and positron emission tomography. We calculated % FDG fractional uptake in the inter-ventricular septum and posterolateral wall. Heterogeneity of FDG uptake was evaluated by % interregional coefficient of variation of FDG fractional uptake in each wall segment. In both the interventricular septum and posterolateral wall, % FDG fractional uptake was not significantly different between the two groups. The % interregional coefficient of variation for both interventricular septum (10.6 +/- 1.6 vs. 4.1 +/- 0.5, p < 0.01) and posterolateral wall (5.9 +/- 0.7 vs. 3.8 +/- 0.5, p < 0.05) was significantly larger in patients with HCM than in HHD patients associated with asymmetrical septal hypertrophy. Echocardiography demonstrated that the degree of asymmetrical septal hypertrophy was similar between the two groups. These results suggest that myocardial glucose metabolism may be more heterogeneous in patients with HCM compared to HHD patients associated with asymmetrical septal hypertrophy, although the left ventricular shape is similar. The difference in the heterogeneity might have resulted from differences in the pathogeneses of the two diseases.

Heterogeneity of myocardial fluoro-18 2-deoxyglucose uptake in patients with apical hypertrophic cardiomyopathy.

We have shown that myocardial glucose metabolism is heterogeneous in patients with hypertrophic cardiomyopathy. It is not known, however, whether glucose metabolism is impaired in patients with apical hypertrophic cardiomyopathy, which is fairly common in Japan. We studied 7 patients with apical hypertrophic cardiomyopathy and 5 normal subjects using fluoro-18 2-deoxyglucose (FDG) and positron emission tomography (PET). We calculated regional FDG fractional uptake and the inter-regional coefficient of variation (CV) of FDG fractional uptake in the interventricular septal, anteroapical, and posterolateral regions. The regional FDG fractional uptake was similar in the 2 groups and among the 3 different segments within each group. However, the inter-regional CV of FDG fractional uptake was increased in the anteroapical wall segment of the patient group compared with the control group and also with the other 2 regions in the patient group. The results did not differ when we studied another 5 patients and 6 normal control subjects with a PET scanner with higher spatial resolution. These data suggest that myocardial glucose metabolism may be impaired in the anteroapical wall segment of patients with apical hypertrophic cardiomyopathy.

Effects of spontaneous myocardial oscillation on cardiac function: direct observation of the epicardial fluorescence image in calcium overloaded isolated hamster hearts.

OBJECTIVES: Calcium overload induces spontaneous cyclic calcium release from the sarcoplasmic reticulum, leading to spontaneous myocardial oscillation. This study was designed to elucidate (1) the effect of the myocardial oscillation on changes in ventricular performance and (2) how these changes relate to the strength of the diastolic spontaneous myocardial oscillation and the spatial extent--that is, in how extensive an area of the epicardium it occurred. METHODS: the isovolumic pressure of the left ventricle and epicardial fura 2 fluorescence in isolated hamster hearts were simultaneously observed at various calcium concentrations ([Ca2+]o). Endothelial cells and pericytes of the capillaries, preferentially stained by fura 2, were passively oscillated by surrounding myocytes during diastole at concentrations greater than 1 mmol/l of [Ca2+]o. The strength of the myocardial oscillation was evaluated as the root mean square (RMS) of fluctuation in the distance between endothelial cells or pericytes. The spatial extent of the myocardial oscillation was estimated as the appearance rate, defined as the ratio of the number of microscopic fields showing the capillary oscillation, to the total number of examined fields. RESULTS: Up to 4 mmol/l of [Ca2+]o, developed pressure and maximum rate of pressure rise significantly increased in a manner dependent on [Ca2+]o, but a further increase in [Ca2+]o significantly decreased these parameters. In the presence of ryanodine (2.5 mumol/l), developed pressure and maximum rate of pressure rise monotonously increased in a manner dependent on [Ca2+]o. Although the oscillation was never observed at 1 mmol/l of [Ca2+]o (appearance rate = 0%), it occurred in some of the microscopic fields at 2 and 4 mmol/l (appearance rate = 19.5 and 56.3%, respectively) and occurred in all microscopic fields at concentrations greater than 4 mmol/l (appearance rate = 100%). Ryanodine, which completely eliminated the capillary oscillation, inhibited the increase of both RMS and end-diastolic pressure by an increase in [Ca2+]o. CONCLUSIONS: Our data suggest that the myocardial oscillation impairs systolic and diastolic function in intact ventricle, and that these effects are associated with the spatial extent and the strength of the myocardial oscillation.

Intracellular calcium modulators for cardiac muscle in pathological conditions.

This is a brief review of agents that stabilize calcium release from the sarcoplasmic reticulum in cardiac muscle. An excess intracellular calcium concentration (calcium overload) is a common feature in a variety of cardiac cell injuries. Calcium overload elicits diastolic and systolic failure, and is involved in the genesis of arrhythmias. These abnormalities appear in part to be caused by the spontaneous release of calcium ions from the sarcoplasmic reticulum. Previous efforts to treat calcium overload were made with the intention to decrease the total intracellular content of calcium ions. However, such procedures would result in a decrease in contractility. Agents that stabilized calcium release from the sarcoplasmic reticulum may therefore be useful to correct abnormalities in calcium overload. In this review, after briefly describing intracellular calcium homeostasis, strategies against calcium overload, especially those involving magnesium ion, ryanodine, caffeine, dantrolene, phenytoin, R56865, KT361 and flunarizine will be discussed.

Effects of chronic right ventricular pressure overload on myocardial glucose and free fatty acid metabolism in the conscious rat.

OBJECTIVE: The aim was to investigate the effects of chronic right ventricular pressure overload on myocardial glucose and free fatty acid metabolism in the right ventricular free wall, ventricular septum, and left ventricular free wall. METHODS: Using a glucose analogue, 14C-2-deoxyglucose (14C-DG), and a fatty acid analogue, 14C-beta methylheptadecanoic acid (14C-BMHDA), quantitative autoradiography was performed in conscious rats with 4 week pulmonary artery constriction. RESULTS: In rats with chronic pulmonary artery constriction, right ventricular peak systolic pressure and right ventricular weight to body weight ratio increased by 88% and 127%, respectively, compared with sham operated rats (P < 0.01 for each). In the right ventricular free wall, 14C-DG deposition increased but 14C-BMHDA accumulation did not differ in the chronic pulmonary artery constricted rats compared with sham operated rats [212(SEM 27), n = 6 v 101(15) nCi.g-1, n = 4, P < 0.01, and 406(40), n = 6, v 333(48) nCi.g-1, n = 4, NS, respectively]. In sham operated rats, 14C-DG and 14C-BMHDA deposition did not differ between the ventricular septum and the left ventricular free wall. In contrast, 14C-DG and 14C-BMHDA accumulations were lower in the ventricular septum compared with the left ventricular free wall wall in chronic pulmonary artery constricted rats. Myocardial blood flow assessed by 14C-iodoantipyrine was homogeneously distributed throughout both ventricles. CONCLUSIONS: Chronic right ventricular pressure overload increases myocardial glucose uptake and/or its phosphorylation in the right ventricular free wall, and alters the regional profiles of substrate use in the ventricular septum and left ventricular free wall despite the homogeneous blood flow distribution. The results of the acute right ventricular pressure overload study, in which only right ventricular 14C-BMHDA deposition was increased compared with controls, suggest that the findings obtained from chronic pulmonary artery constricted rats cannot be explained by increased right ventricular pressure alone.

Quantitative double-tracer autoradiography with tritium and carbon-14 using imaging plates: application to myocardial metabolic studies in rats.

UNLABELLED: A system for 3H- and 14C-labeled macroautoradiography was developed that is able to quantify the tissue radioactivity of two tracers using imaging plates. METHODS: Discrimination between electrons emitted from 3H and 14C is possible on the basis of their different energy distributions. The general use imaging plate with a protective layer detects 14C radioactivity, but it does not detect 3H radioactivity which has a lower energy distribution than 14C. Recently, a 3H-sensitive imaging plate without a protective layer was developed. The 3H distribution image is obtained by subtracting the UR image from the TR image. For quantification of the tissue radioactivity of 3H and 14C, we obtained tissue equivalent values (Bq/mg) of commercially available 3H- and 14C-labeled graded standards using different dilutions of labeled heart paste and liquid scintillation counting. Using the 3H- and 14C-labeled graded standards, we confirmed the validity of the quantification of the 3H-autoradiographic intensity using this subtraction method. We applied this method to a rat model of acute myocardial ischemia to compare regional myocardial free fatty acid uptake determined by beta-methyl[1-14C]heptadecanoic acid to glucose uptake determined by 2-deoxy-D-[1-3H]glucose. RESULTS: Free fatty acid uptake was decreased sharply at the ischemic periphery where glucose uptake was preserved. CONCLUSION: This double-tracer autoradiography with 3H and 14C which has high sensitivity, a high spatial resolution of 50 microns and superior linearity with a wide dynamic range of 10(4) to 10(5) allows accurate quantification of the tissue radioactivity of the two radiopharmaceuticals.

Diversity of early afterdepolarizations in guinea pig myocytes: spatial characteristics of intracellular Ca2+ concentration.

We classified early afterdepolarizations (EADs) into subgroups according to the spatial features of the intracellular Ca2+ concentration ([Ca2+]i). Myocytes were enzymatically isolated from guinea pig ventricles. When fura-2 salt was applied through a whole cell patch pipette after the formation of a gigaohm seal, the membrane potential was measured using the current, clamp technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional microelectrode technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV system. EADs were induced after superfusion with potassium-free Tyrode solution. Irrespective of the fura-2 loading procedure, EADs could be classified into those with spatially synchronous fluorescence changes (n = 26 from eight hearts) and those with heterogeneous changes (n = 20 from three hearts). EADs with synchronous features took off from a higher membrane potential (> or = -34 mV) than EADs with heterogeneous features (< or = -57 mV). These results suggest that EADs have at least two constituents.

Spatial features of calcium transients during early and delayed afterdepolarizations.

Although changes in intracellular Ca2+ concentration ([Ca2+]i) are spatially heterogeneous during spontaneous contraction in mammalian cardiac muscle, it has not yet been observed how [Ca2+]i changes spatially within cardiac myocytes during delayed (DADs) and early (EADs) afterdepolarizations. The aim of this study is to characterize the spatial features of the increase in [Ca2+]i during such afterdepolarizations and to understand the ionic mechanisms responsible for them. Myocytes were enzymatically isolated from guinea pig ventricles and loaded with fura 2-acetoxymethylester, the Ca2+ fluorescence indicator dye. Membrane potential was recorded with a conventional microelectrode technique, and spatiotemporal changes in fura 2 fluorescence and cell length were recorded using a digital television system. After superfusion with potassium-free Tyrode solution, DADs and EADs were induced. During DADs, fluorescence transients were heterogeneous within myocytes (n = 11). Furthermore, they often propagated within myocytes as if they were "waves." In contrast, during EADs, fluorescence transients showed no waves within myocytes but rather showed synchronous changes throughout the myocytes (n = 15). The results of this study suggest that the spatial features of the increase in [Ca2+]i differ between the DADs and EADs. We concluded from these differing features that the ionic mechanisms responsible for the two triggered activities are different.

The source of epifluorescence in isolated perfused heart loaded with fura 2-AM or indo 1-AM.

The purpose of this study is to clarify the kinds of cells that fluoresce in isolated perfused heart intracoronarily loaded with fura 2-AM or indo 1-AM. The hearts from hamsters perfused by the Langendorff method were loaded with fura 2-AM or indo 1-AM intracoronarily. The epicardium was excited by ultraviolet light at a wavelength of 340 or 380 nm (fura 2) or 360 nm (indo 1). Epifluorescent images from arrested hearts prepared with St Thomas' cardioplegic solution were observed through an inverted microscope and taken by a still camera. Endothelial cells and pericytes of the capillaries showed intense fluorescence. In the intercapillary spaces, a less intense but still apparent fluorescence emitted by myocytes could also be detected. On the other hand, fluorescence from smooth muscle cells and fibroblasts could not be identified. Therefore, epifluorescence in the isolated perfused heart loaded with fura 2-AM or indo 1-AM was mainly generated within endothelial cells, pericytes, and myocytes. To evaluate calcium fluorescence in isolated hearts quantitatively, the fluorescence of endothelial cells and pericytes of the capillaries must be taken into consideration.