Pharmacological characterization of chick and frog beta adrenergic receptors in primary cultures of myocardial cells

In membrane preparations derived from primary cultures of chick myocardial cells, beta adrenergic receptors modeled for a single low-affinity site for both betaxolol (beta-1-selective) and ICI 118551 (beta-2-selective) displacement of [125I]iodocyanopindolol (ICYP), indicating that the chick beta receptor is pharmacologically distinct from both mammalian beta-1 and beta-2 adrenergic receptors with respect to these antagonists. However, the highly beta-1-selective compound CGP 20712A was able to distinguish two binding sites on ICYP competition curves, a high-affinity "beta-1 site" (75%) and a low-affinity "beta-2 site" (25%). Also, in chick heart cell membranes the relative ability of agonists to displace ICYP produced a profile typical of beta-1 adrenergic receptors with a rank order of potency or efficacy of: isoproterenol greater than epinephrine = norephinephrine. When agonist-mediated adenylyl cyclase stimulation was assessed the order of potency was slightly different, isoproterenol greater than epinephrine greater than or equal to norepinephrine. Additionally, antagonism of isoproterenol stimulation of adenylyl cyclase by CGP 20712A yielded a Kb value (1.16 +/- 0.35 x 10(-7) M) intermediate between the high and low-affinity binding sites of CGP 20712A, suggesting that the low-affinity site is coupled to adenylyl cyclase. In membrane preparations of frog myocardial cells, ICYP/antagonist competition curves modeled for a mixed population of receptors, with subtype percentages varying from 50:50 beta-1:beta-2 to 100% beta-2 depending on the specific antagonist used and the individual cell preparation. For ICYP/agonist competition binding experiments the relative ability to displace ICYP was isoproterenol greater than epinephrine = norepinephrine, a profile typical of beta-1 adrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Contributions of [Ca2+]i, [Pi]i, and pHi to altered diastolic myocyte tone during partial metabolic inhibition

Ischemia may cause increased or decreased distensibility of the left ventricle, but the cellular mechanisms involved have not been clarified. We examined the possible contributions of changes in intracellular inorganic phosphate, pH, and Ca2+ concentrations to altered diastolic function in cultured myocytes subjected to partial metabolic inhibition. Paced cultured embryonic chick and adult rabbit ventricular myocytes superfused with 20 mM 2-deoxyglucose (2DG) exhibited an increase in end-diastolic intracellular free calcium concentration ([Ca2+]i) and an upward shift in end-diastolic cell position. These results indicate that glycolytic blockade increases diastolic and systolic calcium in paced ventricular myocytes, and that this elevated diastolic calcium influences the extent of diastolic relaxation. In contrast, paced ventricular myocytes superfused with 1 mM cyanide (CN) exhibited a similar increase in end-diastolic [Ca2+]i but a decrease in end-diastolic cell position and amplitude of motion. Although changes in ATP contents were similar in both groups (2DG, -29.9%; CN, -40.1%), alterations of intracellular pH and inorganic phosphate concentrations were different. In 2DG-treated cells, pHi did not decrease significantly (7.18 +/- 0.04 to 7.12 +/- 0.11, n = 14) but in the CN group it decreased markedly within 6 min (7.18 +/- 0.04 to 6.76 +/- 0.11, n = 11, P less than 0.01). Intracellular inorganic phosphate decreased slightly in the 2DG group (-14.8%, NS) but increased in cells exposed to CN (45.7%, P less than 0.02). We conclude that while a prominent increase in diastolic [Ca2+]i occurs in rapidly paced ventricular myocytes exposed to either inhibitors of glycolysis or oxidative phosphorylation, the effects of this increase in [Ca2+]i on diastolic distensibility may be influenced by intracellular accumulation of metabolites that decrease the sensitivity of myofilament to [Ca2+]i.

Lysophosphatidylcholine increases cytosolic calcium in ventricular myocytes by direct action on the sarcolemma

Lysophosphatidylcholine (LPC) accumulates in myocardial tissues during ischemia, and has toxic effects which may contribute to the arrhythmias and relaxation abnormalities that occur during acute ischemia. These effects of LPC may be mediated in part by calcium overload. To test this hypothesis, spontaneously contracting cultured embryonic chick ventricular myocytes were superfused with various concentrations of LPC (10, 50 and 100 microM) while effects on contractile motion (video motion detector) and changes in free intracellular calcium ion concentration ([Ca2+]i indo-1 fluorescence) were determined. At concentrations greater than or equal to 10 microM, a dose-related, time-dependent effect occurred after exposure to LPC, consisting of the development of contracture and marked elevation of [Ca2+]i. LPC also produced a dose-related, time-dependent inhibition of K+ uptake, indicating there was inhibition of the Na(+)-K+ ATPase Na+ pump. However, the LPC-induced increase in [Ca2+]i was not due to Na+ overload caused by inhibition of the Na(+)-K+ ATPase Na+ pump because superfusion with a zero-Na+ solution did not prevent an increase in [Ca2+]i after LPC exposure; and the increase in [Ca2+]i after exposure to LPC occurred too rapidly to be accounted for by Na+ pump inhibition. Removal of extracellular Ca2+ prevented the rise in [Ca2+]i, after exposure to LPC but treatment with verapamil failed to inhibit the increase in [Ca2+]i induced by LPC. We conclude that LPC produces contracture due to an increase [Ca2+]i. These effects are seen at concentrations of 10 microM and greater, are not due to altered Na(+)-K+ ATPase Na+ pump or calcium channel function, and are probably related to the detergent properties of this amphiphile. There effects may account in part for myocardial dysfunction during ischemia in intact tissue.

Evidence that binding of Indo-1 to cardiac myocyte protein does not markedly change Kd for Ca2+

Quantitative measurement of [Ca2+]i with the fluorescent Ca(2+)-indicators Indo-1 and Fura-2 is complicated by the possibility that the value of the dissociation constant (Kd) may be influenced by binding to intracellular proteins. We investigated this question in cultured chick ventricular myocytes by use of two different Indo-1 calibration methods. First, the Indo-1 fluorescence ratio (R) (400/500 nm) was measured in beating myocytes loaded by exposure to Indo-1/AM. Then, cells were exposed to the Ca2+ ionophore Br A-23187 and fluorescence ratio was measured in the presence of 500 nM Ca2+ (EGTA-Ca2+ buffer). Subsequently cells were permeabilized to Ca2+ by a 1 min exposure to 25 microM digitonin in the presence of 'zero' Ca2+ (10 mM EGTA) and saturating 1 mM Ca2+ to obtain Rmin, Rmax and beta. We then calculated [Ca2+]i from the formula ([Ca2+]i = Kd [( R - Rmin)/(Rmax - R)]beta). With Kd = 250 nM, calculated systolic [Ca2+]i was 750 +/- 44 nM and diastolic 269 +/- 19 nM (means +/- SEM, n = 16). The R value calculated for an assumed [Ca2+]i = 500 nM using the above formula and digitonin derived constants was very similar to the value measured using Br A-23187 (digitonin, 0.67 +/- 0.03: Br A-23187, 0.66 +/- 0.03, ns). As the Br A-23187 method is independent of the value chosen for Kd, we conclude that the Kd of 250 nM for Indo-1 measured in free solutions closely approximates the Kd for intracellular Indo-1 in these cells, and that therefore the Kd of Indo-1 for Ca2+ does not appear to be markedly affected by binding to proteins or other intracellular molecules.

Myocyte injury and contraction abnormalities produced by cytotoxic T lymphocytes

BACKGROUND

The mechanisms by which ventricular function is altered during cardiac transplant rejection are not well understood. Therefore, an in vitro model system has been developed to facilitate investigation of lymphocyte-mediated myocyte injury.

METHODS AND RESULTS

Splenic lymphoid cells were obtained from mice 8-10 days after placement of a vascularized abdominal cardiac allograft and were restimulated in vitro with irradiated donor-type splenocytes for 5 days. Cytotoxic effects of these allogenically stimulated lymphocytes on syngeneic and donor strain fetal cultured myocytes were determined by a 51Cr release assay at different lymphocyte to myocyte ratios. 51Cr release from donor strain myocytes was detectable within 1 hour of exposure, was maximal by 3-5 hours of coincubation with sensitized lymphocytes, and was allospecific. Cell injury manifest by 51Cr release was calcium dependent and was inhibited by pretreatment of lymphocytes with phorbol ester to deplete protein kinase C. Myocyte injury was also prevented by pretreatment of sensitized lymphocytes with anti-Thy 1.2 or anti-CD8 antibody plus complement but not by treatment with anti-CD4 antibody, indicating that CD8+ cytotoxic T cells are involved. Altered myocyte contractile motion preceded myocyte lysis (51Cr release), was characterized by an initial reversible decrease in amplitude of contraction, and was followed by rapid and irregular beating with eventual complete cessation of contraction. Contractile alterations induced by sensitized lymphocytes were inhibited by elimination of CD8+ cells.

CONCLUSIONS

Myocyte injury can be produced by sensitized cytotoxic T lymphocytes in vitro and is calcium and protein kinase C dependent. The contractile abnormalities produced appear to be similar to those observed in cardiac transplant patients undergoing rejection, and thus this model system promises to allow investigation of the mechanisms involved.

Mechanisms of reoxygenation injury in cultured ventricular myocytes

To investigate factors contributing to reperfusion and reoxygenation myocardial injury, we exposed layers of cultured chick ventricular myocytes to severe hypoxia for up to 3 hours in the presence of 20 mM 2-deoxyglucose, zero glucose, and 5 mM pyruvate, and then exposed the myocytes to reoxygenation. Lactate dehydrogenase (LDH) release was moderately increased during 3 hours of hypoxia but was increased markedly during reoxygenation. Coincident changes in intracellular calcium concentration ([Ca2+]i) and cell motion were also measured during hypoxia and reoxygenation. During hypoxia, [Ca2+]i increased to more than 1 microM, and with reoxygenation, [Ca2+]i abruptly decreased slightly but remained elevated more than 1 microM. Cells developed a stable rigor after 30 minutes of hypoxia. Reoxygenation caused a marked hypercontracture within 5 minutes. Pretreatment of myocytes with either 2,3-butanedione monoxime, which inhibits Ca2(+)-dependent force development, or cyanide inhibited reoxygenation hypercontracture. LDH release after reoxygenation was also significantly reduced in the presence of 2,3-butanedione monoxime. Treatment of myocytes with superoxide dismutase and catalase during hypoxia also resulted in a decrease in LDH release during reoxygenation. We conclude that an abrupt increase in [Ca2+]i during reoxygenation does not account for reoxygenation injury. However, in the presence of elevated [Ca2+]i, reoxygenation and the resulting probable resynthesis of ATP causes [Ca2+]i-dependent myofilament crossbridge cycling, and the resulting hypercontracture contributes to myocyte damage. The generation of oxygen free radicals after reoxygenation also appears to contribute to cell injury in this system.

Activation of furosemide-sensitive K+ fluxes in myocytes by ouabain and recovery from metabolic inhibition

Modulation of transsarcolemmal K+ flux mediated by the furosemide-sensitive K(+)-Cl- (or Na(+)-K(+)-Cl-) cotransport carrier was studied in cultured chick embryo ventricular cells. We defined at least three distinct K+ efflux pathways: 1) a Ba2(+)-sensitive efflux component, probably reflecting K+ movement through K+ channels; 2) a furosemide-sensitive component, reflecting K(+)-Cl- cotransport; and 3) a component insensitive to both Ba2+ and furosemide. With respect to K+ influx, there were 1) a ouabain-sensitive K+ uptake presumably mediated by Na(+)-K(+)-adenosinetriphosphatase and 2) a furosemide-sensitive K+ uptake. The effects of elevation of intracellular calcium concentration ([Ca2+]i) on Ba2+ and furosemide-sensitive K+ flux pathways were studied. Elevation of [Ca2+]i had minor effects on Ba2(+)-sensitive K+ flux. However, elevation of [Ca2+]i produced by exposure to ouabain for 60 min activated a furosemide-sensitive 42K+ efflux and a ouabain-resistant, furosemide-sensitive 42K+ influx. The activation of K+ influx, caused by an increase in [Ca2+]i, was completely inhibited by ATP depletion (produced by exposure to ouabain and metabolic inhibitors simultaneously) and was partially inhibited by the calmodulin inhibitor W7. Activation of the furosemide-sensitive K+ flux was also produced by washout of metabolic inhibitors, a condition in which ATP resynthesis occurs in the presence of an increased [Ca2+]i. Activation of furosemide-sensitive K+ fluxes by exposure to ouabain or washout of metabolic inhibitors caused a net K+ loss, which accounts in part for the cell shrinkage noted during recovery from metabolic inhibition in previous studies. These results suggest that [Ca2+]i and intracellular ATP concentration are important in the regulation of furosemide-sensitive K+ flux in these cells, perhaps via the involvement of a Ca2(+)-calmodulin-dependent protein kinase.

Contribution of endothelial cells to calcium-dependent fluorescence transients in rabbit hearts loaded with indo 1

In studies that attempt to measure intracellular calcium [( Ca2+]i) in the intact heart with the calcium indicator indo 1-AM, a fundamental assumption is that the signals report changes in myocyte [Ca2+]i. We studied isolated perfused rabbit hearts loaded with the calcium probe indo 1-AM and recorded surface fluorescence of the left ventricle during continuous excitation at 360 nm. In cells containing indo 1, an increase in [Ca2+]i is associated with an increase in fluorescence intensity at 400 nm, a decrease in intensity at 500 nm, and an increase in the 400:500 nm ratio. Beat-to-beat fluorescence transients were recorded from the surface of the heart coincident with contraction, indicating that a component of the fluorescence signals is derived from beating myocytes. To evaluate the potential contribution of endothelial cells, we compared the response to increases in [Ca2+]o or bradykinin (10(-5) M). In response to an increase of the [Ca2+] in the perfusate from 0.6 to 3.0 mM, left ventricular developed pressure and +dP/dt increased with a simultaneous increase in the [Ca2+]i-sensitive 400:500 nm ratio. Perfusion with the endothelial cell agonist bradykinin caused no change in left ventricular isovolumic peak systolic pressure or left ventricular dP/dt, whereas bradykinin evoked an immediate elevation in both the diastolic and systolic levels of the [Ca2+]i-sensitive 400:500 nm ratio. In additional experiments with indo 1-loaded isolated beating myocytes, superfusion with bradykinin had no effect on either the fluorescence [Ca2+]i transients or contractility. In contrast, superfusion of indo 1-loaded cultured endothelial cells with bradykinin caused the elevation of [Ca2+]i within seconds. Fluorescence microscopy of unstained frozen tissue sections from indo 1-loaded hearts also suggested the presence of more intense microvascular endothelial cell indo 1 fluorescence relative to that observed in myocytes. These experiments provide evidence that a component of [Ca2+]i-sensitive fluorescence of whole hearts loaded with indo 1 is contributed by nonmyocyte sources, including endothelial cells. These results also raise the caution that the abrupt rise of [Ca2+]i that has been observed during the initial phase of ischemia in whole hearts loaded with indo 1 may be partly derived from endothelial cells rather than myocytes.

Effects of intracellular acidosis on [Ca2+]i transients, transsarcolemmal Ca2+ fluxes, and contraction in ventricular myocytes

We examined the effects of intracellular acidosis produced by washout of NH4Cl on [Ca2+]i transients (indo-1 fluorescence), cell contraction (video motion detector), and 45Ca and 24Na fluxes in cultured chick embryo ventricular myocytes. Exposure of cells to 10 mM NH4Cl produced intracellular alkalosis (pH 7.6), and subsequent washout resulted in a transient acidosis (pH 6.5). Exposure to 10 mM NH4Cl slightly decreased [Ca2+]i transients but increased the amplitude of cell contraction. Subsequent washout of NH4Cl initially increased diastolic [Ca2+]i and decreased the peak positive and negative d[Ca2+]i/dt, while the amplitude of cell contraction was markedly decreased. Subsequently, peak systolic [Ca2+]i increased with partial recovery of contraction. A similar increase in [Ca2+]i and decrease in contraction after washout of NH4Cl was observed in single paced adult guinea pig ventricular cells. Acidosis decreased 45Ca uptake by sarcoplasmic reticulum vesicles isolated from chick embryo ventricle. However, the [Ca2+]i increase caused by intracellular acidosis was also observed in the presence of 10 mM caffeine, suggesting that altered sarcoplasmic reticulum handling of calcium is not the only mechanism involved. Intracellular acidosis only slightly increased total 24Na uptake under these conditions, an effect resulting from the combination of a stimulation of amiloride-sensitive sodium influx (Na(+)-H+ exchange) and inhibition of sodium influx via Na(+)-Ca2+ exchange, manifested by a significant decrease in 45Ca efflux. Further support for a lack of involvement of an increased [Na+]i in the observed increase in [Ca2+]i during acidosis was low-sodium, nominal 0-calcium extracellular solution, an experimental condition that minimizes the possible effects of Na(+)-H+ exchange and Na(+)-Ca2+ exchange. We conclude that the [Ca2+]i increase caused by intracellular acidosis in cultured ventricular cells is primarily due to changes in [Ca2+]i buffering and [Ca2+]i extrusion, rather than to an increase in transsarcolemmal calcium influx. Intracellular acidosis also markedly decreases the sensitivity of the contractile elements to [Ca2+]i in cultured chick embryonic and adult guinea pig ventricular myocytes.

Accurate determination of the transaortic valve gradient using simultaneous left ventricular and femoral artery pressures

Accurate determination of the transaortic valve gradient has required two catheters, one in the left ventricle and one in the ascending aorta. We now report a new technique for measurement of the transaortic valve gradient from the simultaneous left ventricular (LV) and femoral artery (FA) pressure tracings. This technique was compared with the "true" gradient obtained by measurement of the simultaneous LV and central aortic pressures, and is accurate (R = 0.999) and relatively simple. Other approaches used to determine the mean transaortic valve gradient were less accurate: simultaneous LV-FA (R = 0.991); aligned LV-FA (R = 0.974); averaged simultaneous and aligned LV-FA (R = 0.981); and nonsimultaneous LV-aorta pullback (R = 0.953). Thus, this new technique provides an accurate transaortic valve gradient without requiring the use of two central catheters.

Detection of La3+ influx in ventricular cells by indo-1 fluorescence

We exposed indo-1-loaded cultured embryonic chick ventricular cells to 0.03-1.0 mM extracellular lanthanum concentration ([La3+]o) and simultaneously measured cell contractile motion and the 410/480 nm fluorescence intensity ratio. After exposure to La3+, ventricular cells stopped contracting and relaxed within seconds, and the 410/480 fluorescence ratio increased. The increase in the 410/480 signal was related to [La3+]o but was not affected by short exposures to zero extracellular calcium concentration ([Ca2+]o) or caffeine, suggesting that the fluorescence was not caused by a La3+-induced increase in intracellular calcium concentration ([Ca2+]i) but rather to increased intracellular lanthanum concentration ([La3+]i). In vitro studies confirmed that indo-1 fluorescence was sensitive to La3+. The increase in [La3+]i in 0.1 mM [La3+]o was directly related to intracellular sodium concentration ([Na+]i), suggesting that La3+ entered cells via Na+-La3+ exchange. In contrast to ventricular cells, which have a functionally distinct Na+-Ca2+ exchange system, exposure of indo-1-loaded cultured bovine endothelial cells to La3+ failed to produce an increase in [La3+]i. These results indicate that exposure of ventricular cells to 0.1-1.0 mM [La3+]o results in a [La3+]i greater than 250 nM within 1 min. Therefore, changes in myocardial 45Ca2+ fluxes and contents induced by La3+ cannot be ascribed solely to extracellular La3+ effects.

Mechanism of protective effects of Ca++ channel blockers on energy deprivation contracture in cultured ventricular myocytes

To examine mechanisms of the protective effects of Ca++ channel blockers on energy deprivation contracture, we measured cystolic calcium ion concentration ([Ca++]i) (Indo-1 fluorescence), development of contracture (video motion detector) and ATP contents during exposure of cultured chick embryo ventricular cells to 1 mM cyanide (CN) and 20 mM 2-deoxyglucose (2-DG). The time periods required for [Ca++]i to reach 50% of [Ca++]i transient ([Ca++]i-50) and contracture were determined after exposure to 1) CN + 2-DG alone, 2) CN + 2-DG simultaneous with 1 microM verapamil (V-sim) and 3) verapamil followed by CN + 2-DG (V-pre). Time periods required to reach [Ca++]i-50 under these conditions were 4.2 +/- 0.4 min (CN + 2-DG alone), 3.8 +/- 0.4 min (NS vs. CN + 2-DG alone) (V-sim) and 6.4 +/- 1.1 min (P less than .05 vs. CN + 2-DG alone) (V-pre), respectively. Time periods required for contracture development were 4.4 +/- 0.3 min (CN + 2-DG alone), 4.4 +/- 0.6 min (NS vs. CN + 2-DG alone) (V-sim) and 9.3 +/- 1.2 min (P less than .05 vs. CN + 2-DG alone) (V-pre). Three minutes after metabolic inhibition, ATP contents declined from 32.3 +/- 0.7 nmol/mg of protein to 4.2 +/- 1.0 in CN + 2-DG alone, to 4.5 +/- 0.9 (NS vs. CN + 2-DG alone) with V-sim and to 8.3 +/- 2.2 (P less than .05 vs. CN + 2-DG alone) with V-pre.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of three techniques for percutaneous balloon aortic valvuloplasty of aortic stenosis in adults

Three different techniques for percutaneous balloon aortic valvuloplasty h have been described: retrograde single balloon, retrograde double balloon, and antegrade techniques. This report describes our experience using the three techniques in twenty-five consecutive procedures. All techniques resulted in a significant decrease in transvalvular pressure gradient and an increase in calculated aortic valve area, without significant difference among the three. There was no increase in the degree of aortic regurgitation after valvuloplasty by any of the techniques. Vascular complications occurred only with the retrograde double balloon technique. Cardiac tamponade during balloon inflation occurred with both the retrograde single and double balloon techniques. Three deaths occurred; two during the antegrade technique and one after the retrograde double balloon technique. Thus, balloon aortic valvuloplasty can be effectively performed using any of the three techniques. However, the differing techniques have inherent advantages in specific situations, as well as potential complications.

Effects of contrast media on calcium transients and motion in cultured ventricular cells

To investigate the mechanisms of the negative inotropic effects of contrast media, we superfused spontaneously contracting cultured chick embryo ventricular cells with Renografin-76 and iohexol (12% solutions), and hypertonic sucrose during simultaneous measurement of [Ca2+]i transients (indo-1) and motion (video-motion detector system). Exposure to contrast agents caused a significant reduction of contractility, with Renografin-76 having a much greater effect on amplitude of motion than iohexol. Renografin-76 significantly depressed [Ca2+]i transient amplitude, whereas iohexol had no effect. Addition of Ca2+ to correct for calcium binding by Renografin-76 completely reversed its depression of [Ca2+]i transients but only partially reversed the negative inotropic effects. Hypertonic sucrose caused a significant decrease in contraction amplitude, with no significant effects on [Ca2+]i transient amplitude. We conclude that the marked negative inotropic effect of Renografin-76 is caused by both calcium binding and hypertonicity. The less marked depression of contractility produced by iohexol likely is a result of hypertonicity and not caused by alteration of [Ca2+]i.

Effect of reperfusion on electrocardiographic and enzymatic infarct size: results of a randomized multicenter study of intravenous anisoylated plasminogen streptokinase activator complex (APSAC) versus intracoronary streptokinase in acute myocardial infarction

The effect of early coronary artery reperfusion on ECG and enzymatic parameters was examined in 240 patients with acute myocardial infarction. These patients had participated in a randomized trial comparing intravenous anisoylated plasminogen streptokinase activator complex (APSAC) (n = 123) and intracoronary streptokinase (n = 117) therapy. Reperfusion occurred in 59 of 115 (51%) patients receiving APSAC and 67 of 111 (60%) patients receiving streptokinase (p = NS). There was greater early resolution of ST segment elevation in the reperfused than in the nonreperfused patients (p less than or equal to 0.003) and more rapid Q wave evolution (p less than or equal to 0.03). Sigma Q was lower in reperfused than in nonreperfused patients at 8 hours (1.41 +/- 1.18 versus 2.11 +/- 2.10 mV; p less than or equal to 0.05) and at 24 hours (1.43 +/- 1.25 mV versus 2.08 +/- 1.88 mV; p less than or equal to 0.02). Time to peak level was shorter in the reperfused patients for creatine kinase (CK) (10.7 +/- 5.5 hours versus 14.9 +/- 5.9 hours; p less than 0.0001) and lactic acid dehydrogenase (LDH) (29.6 +/- 13.6 hours versus 34.4 +/- 10.5 hours; less than or equal to 0.03) enzymes. Peak LDH-1 was lower in the reperfused group (274 +/- 149 U/L versus 341 +/- 173 U/L; p less than or equal to 0.04). Reperfusion at a mean of 3.9 hours after the onset of infarction was associated with more rapid resolution of ST segment elevation, faster Q wave evolution, smaller ECG infarct size, earlier cardiac enzyme release, and smaller enzymatic infarct size than later or no reperfusion.

Dependence of assessment of coronary artery reperfusion during acute myocardial infarction on angiographic criteria and interobserver variability

The angiographic films of 240 patients with acute myocardial infarction were studied in a randomized trial of intravenous anisoylated plasminogen streptokinase activator complex (APSAC) versus intracoronary streptokinase therapies. The interobserver variability of grading coronary artery perfusion by the Thrombolysis in Myocardial Infarction Study Group (TIMI) criteria was measured as well as the effect of different definitions of reperfusion on the determination of reperfusion rate. There was good agreement in the reading of infarct artery flow grades between 2 blinded observers for each grade considered separately (k = 0.726 +/- 0.014) and for grades 0 or 1 (no perfusion) versus grades 2 or 3 (perfusion) (k = 0.905 +/- 0.011). Discordance between grades 0 or 1 versus 2 or 3 occurred in 74 (5%) of the 1,615 angiographic readings. Discrepancies of clinical significance which affected qualification for study entry, reperfusion or reocclusion status occurred in only 15 patients (6%). Grade 1 flow was found to have the most variable interpretation. Reperfusion rates for APSAC and streptokinase differed significantly when reperfusion was defined by 3 different criteria. The reperfusion rate ranged from 51 to 72% for APSAC and from 60 to 75% for streptokinase depending upon criteria selected. For comparison of the results of different thrombolytic studies, a standard semiquantitative system for grading infarct artery perfusion should be used, readings should be blinded and the criteria used for the definition of reperfusion should be clearly specified.

Alterations in cation homeostasis in cultured chick ventricular cells during and after recovery from adenosine triphosphate depletion

Alterations in cation homeostasis during and after recovery from myocardial ischemia may account for some of the reversible and irreversible components of myocardial cell injury. To investigate possible mechanisms involved, we exposed cultured layers of spontaneously contracting chick embryo ventricular cells to media containing 1 mM cyanide (CN) and 20 mM 2-deoxyglucose (2-DG), and zero glucose for up to 6 h, and then allowed cultured cells to recover in serum-free culture medium for 24 h. Changes in Na, K, and Ca contents, 42K uptake and efflux, ATP content, cell water content, and lactate dehydrogenase (LDH) release were measured, and compared with changes produced by exposure to 10(-3) M ouabain and severe hypoxia. Exposure to CN and 2-DG caused marked increase in cell Na (sevenfold) and Ca (fivefold) contents, and a decrease in K content (one-fifth normal), coincident with ATP depletion to one-tenth normal levels. This produced only slight cell injury, evidenced by increased LDH release. Recovery for 24 h resulted in return to near normal values (expressed in nanomoles per milligram of protein) of Na, Ca, and ATP contents. However, there was failure of cell K content to return to normal, associated with a persistent reduced net uptake of 42K, and an increase in the rate of 42K efflux. These abnormalities in K homeostasis were associated with a decrease in cell volume and water content per milligram of protein. More marked ATP depletion (to 1/100 normal values) was produced by hypoxia plus 2-DG and zero glucose, and was associated with much more severe cell injury manifested by LDH loss. Ouabain exposure resulted in a much greater Ca gain (20-30-fold), relative to increase in Na content, than did either CN and 2-DG or hypoxia; and ouabain effects were not reversible (after a 15-fold or greater increase in Ca content was produced) and were associated with significant LDH release. We conclude that these cells are resistant to cell injury caused by moderately severe Ca overload and ATP depletion produced by exposure to CN and 2-DG. However, metabolic inhibition of ATP production produces persistent abnormalities in K homeostasis, associated with functional abnormalities.

Simultaneous measurement of calcium transients and motion in cultured heart cells

The fluorescent Ca2+ probe indo-1 is a new intracellular Ca2+ concentration [( Ca2+]i) indicator that may be suitable for measurement of [Ca2+]i transients in intact heart cells. We exposed spontaneously contracting cultured chick embryo ventricular cells (37 degrees C) to the membrane-permeable indo-1-acetoxymethyl ester (indo-1 AM). Indo-1 loading was associated with a decrease in the amplitude of contraction measured with a video motion detector, but contractility returned to control levels during a subsequent 30-min wash. Analysis of emission spectra of dye obtained by digitonin permeabilization of cells loaded in indo-1 AM showed that the active intracellular dye was not pure indo-1 but probably includes partially deesterified molecules. With the use of an inverted X40 objective epifluorescence system, washed cells containing indo-1 were excited at 360 nm, and fluorescence intensity was measured at 410 nm (increases with increasing [Ca2+]) and 480 nm (decreases with increasing [Ca2+]). Calibration of the [Ca2+]i signals, reflected by the ratio of 410 to 480 nm fluorescence, was achieved by use of ethylen-glycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA)-Ca2+ buffered solutions containing the nonfluorescent Ca2+ ionophore Bromo-A23187. Average end-diastolic and peak-systolic [Ca2+]i were 328 +/- 32 and 813 +/- 72 nM (means +/- SE, n = 8). The onset of the [Ca2+]i transient preceded motion by 27 +/- 5 ms (means +/- SE, n = 4), but generally resembled the motion signals in contour. These findings indicate that indo-1 may be used to detect [Ca2+]i transients in isolated ventricular cells without causing significant alterations in mechanical performance.

Role of changes in [Ca2+]i in energy deprivation contracture

Mechanisms of energy deprivation contracture were investigated in cultured chick embryo ventricular cells. In the presence of zero-extracellular-Na+, (choline chloride substitution)-nominal-zero-Ca2+ [( Ca2+] approximately 5 microM), exposure of ventricular cells to 1 mM cyanide (CN) and 20 mM 2-deoxyglucose (2-DG)-zero-glucose solution resulted in the development of a contracture (video motion detector) in 5.9 +/- 0.5 minutes. Early after contracture development, the resupply of extracellular Na+, in the continued presence of CN + 2-DG, resulted in a rapid partial relaxation (t1/2 = 1.9 +/- 0.3 seconds), associated with an increase in 45Ca efflux, presumably due to transsarcolemmal Ca2+ extrusion due to Na+-Ca2+ exchange. Resupply of glucose and removal of CN + 2-DG, in the continued absence of Na+, resulted in an initially slower (t1/2 = 11.6 +/- 2.5 seconds), but more complete relaxation of contracture, which was not associated with increased Ca2+ efflux. Pretreatment with 20 mM caffeine delayed the onset of contracture (9.2 +/- 1.1 minutes) and resulted in a contracture that could not be relaxed by resupply of external Na+ only. Studies using the fluorescent Ca2+ probe indo 1 demonstrated that in zero-Na+-zero-Ca2+ solutions, contracture due to CN + 2-DG was associated with an initial rise in [Ca2+]i but that this did not account for all of contracture force development. In cells exposed to CN + 2-DG in the presence of normal extracellular Na+ and Ca2+ concentrations, a small rise in [Ca2+]i was associated with initial contracture development, consistently preceding the development of a larger accelerated contracture presumably due to ATP depletion.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of myocardial cell injury during ischemia and reperfusion

Ischemia in myocardial tissue results in impaired high energy phosphate production and diminished perfusion of the interstitial space. Reduction in the supply of ATP to the sarcolemmal and sarcoplasmic reticulum Na+ and Ca2+ pumps results in a rise in intracellular (Ca2+), which can exceed normal systolic levels within 10 to 15 minutes. Elevated (Ca2+)i can cause activation of proteases and phospholipases, which can damage the sarcolemma and release toxic metabolites, such as lysophospholipids. Oxygen free radicals can be produced by breakdown of nucleosides and accumulate in the interstitial space. Accumulation of metabolites intracellularly can cause cell swelling, which in addition to rigor due to ATP depletion, can stress the weakened sarcolemma, producing cell rupture and death. With reperfusion, additional injury to the myocyte may occur. Resupply of oxygen can result in a burst of oxygen free radical production. Resynthesis of ATP may sensitize the myofilaments to Ca2+, resulting in a hypercontracture that can further promote cell rupture. Resupply of ATP and washout of H+ may cause activation of Na/Ca2+ exchange, thus intensifying Ca2+ overload. Washout of the hypertonic interstitial space fluid may aggravate cell swelling and produce sarcolemmal rupture. Prevention or alteration of ischemic and reperfusion injury in myocardial cells is important clinically. Strategies currently being explored include reducing the rise in (Ca2+)i, which occurs during ischemia and reperfusion; inhibiting the actions of phospholipase on the cell membrane; decreasing free radical effects; and reducing stress on the sarcolemmal by prevention of cell swelling and hypercontracture.

Comparison of simultaneous electrophysiologic and mechanical effects of verapamil and nifedipine in cultured chick embryo ventricular cells

In order to examine possible differences in mechanisms of action of nifedipine and verapamil, simultaneous recordings of membrane potential and cell motion were made during exposure of cultured chick embryo ventricular cells to these drugs. Both verapamil and nifedipine produced a rapid negative inotropic effect and excitation-contraction coupling delay presumably related to the ability of both agents to inhibit Ca2+ influx via the slow Ca channel, and thus decrease the [Ca2+]i transient. However, for an equivalent negative inotropic effect, verapamil produced relatively more membrane diastolic depolarization and slowing of repolarization than did nifedipine. Verapamil also produced a more marked decrease in +dV/dtmax. In ion flux studies, it was demonstrated that verapamil produced a significant inhibition of 24Na influx, relative to control, whereas nifedipine did not. Verapamil also produced a slight decrease in 42K efflux, of borderline significance. These findings support previous results which indicate there are differences in the mechanisms of action of these Ca2+-channel blocking drugs.

Effects of ryanodine and caffeine on contractility, membrane voltage, and calcium exchange in cultured heart cells

To investigate the mechanisms of action of ryanodine and caffeine, changes in mechanical and electrical activity caused by these agents were correlated with alterations in 45Ca fluxes and cell Ca contents in chick embryo ventricular cell monolayer cultures. Ryanodine (10(-10)-10(-5) M) irreversibly decreased contraction amplitude by 10-70% relative to control in a concentration-dependent manner with minimal effects on electrical activity. Ryanodine caused a slight decrease in rapid 45Ca uptake, but no change in total exchangeable calcium content or rapid 45Ca efflux. Caffeine (1-20 mM) caused a transient (less than 10 seconds) 5-12% increase in contraction amplitude followed by a sustained 9-76% decrease in contraction amplitude and a 10 mV decrease in diastolic membrane voltage. Caffeine caused a decrease in rapid 45Ca uptake, a decrease in total exchangeable calcium content, and an increase in rapid 45Ca efflux. These results suggest that caffeine produces a decrease in sarcoplasmic reticulum (SR) Ca2+ uptake, and/or an increase in SR Ca2+ release that eventually depletes the SR of Ca2+, presumably accounting for the negative inotropic effect. The ryanodine effects on contraction are more difficult to account for solely in terms of alterations of transsarcolemmal Ca2+ fluxes and Ca2+ contents. Our data indicate an important role for the SR in excitation-contraction coupling in cultured chick embryo ventricular cells and suggest that SR Ca2+ is part of the rapidly exchanging Ca2+ compartment noted in 45Ca flux studies.

Dynamic variations in resistance of coronary arterial narrowings in angina pectoris at rest

The coronary hemodynamic events in 4 patients with frequent episodes of spontaneous rest angina were investigated. The basal coronary transstenotic pressure gradients showed more severe stenosis than that seen on coronary arteriography, suggesting that angiography in this setting may underestimate the true extent of coronary atherosclerosis. Episodes of angina were triggered by marked, sudden increases in the transstenotic coronary pressure gradient and a decrease in coronary blood flow without alterations in systemic arterial pressure or heart rate. These changes in coronary hemodynamics were promptly reversed by the intracoronary administration of nitroglycerin. No such spontaneous variations in transstenotic coronary pressure gradients were observed in 37 patients with a history of classic exertional angina but no rest angina. These unique data represent direct hemodynamic evidence that an increase in resistance at the site of a coronary stenosis, most likely the result of an increase in arterial tone, can be a cause of transient myocardial ischemia in patients with angina at rest.