Effects of lysophosphatidylcholine on cultured heart cells: correlation of rate of uptake and extent of accumulation with cell injury.

In this study we evaluated the effects of lysophosphatidylcholine, a possible mediator of ischemic damage, on cultured neonatal rat heart cells. The rate and duration of lysophosphatidylcholine accumulation was correlated with Ca++ uptake and cell injury. The rate of carbon 14-labeled lysophosphatidylcholine accumulation during superfusion of the cells by 10 to 100 mumol/L 14C-labeled lysophosphatidylcholine was proportional to the concentration of lysophosphatidylcholine in the perfusate. Rapid accumulation of lysophosphatidylcholine (0.235 nmol/mg protein per minute), which occurred during 10 minutes of exposure to 100 mumol/L lysophosphatidylcholine, resulted in Ca++ overload and cell lysis. In contrast, slow accumulation of lysophosphatidylcholine by myocytes, which occurred during prolonged (1 hour) exposure to a sublethal micellar concentration (80 mumol/L) or very prolonged exposure (6 hours) to a submicellar concentration of lysophosphatidylcholine (10 mumol/L) did not result in Ca++ overload or irreversible injury despite more total lysophosphatidylcholine accumulation than during a single 10-minute exposure to 100 mumol/L lysophosphatidylcholine (p less than 0.005). Repeated brief exposures (5 minutes) to 100 mumol/L lysophosphatidylcholine separated by 20-minute recovery intervals also resulted in more lysophosphatidylcholine accumulation than during the lethal 10-minute exposure to 100 mumol/L lysophosphatidylcholine but did not result in irreversible injury. We therefore conclude that cardiac myocytes can tolerate slow accumulation of lysophosphatidylcholine and that factors other than the quantity of lysophosphatidylcholine accumulating in cells are determinants of the degree of injury sustained from exposure to lysophosphatides.

A fixation procedure suitable for autoradiography of endogenous long-chain acyl carnitine.

A tissue processing procedure was evaluated for fixation of endogenous long-chain acyl carnitine (LCA) to facilitate autoradiographic subcellular localization of this amphiphile. Suspensions of neonatal rat myocytes labeled with exogenous 14C-palmitoyl carnitine retained 85.2% of the radiolabel after tissue processing. Autoradiography demonstrated no significant translocation of radiolabeled LCA from myocytes to unlabeled sheep erythrocytes mixed in equal proportions and processed together. To evaluate endogenous LCA fixation, cultured myocytes were incubated for 3 days with 3H-carnitine. Radioactivity was distributed in LCA, short-chain acyl carnitine, and free carnitine pools in proportion to the physiological concentrations of the metabolites traced. Before tissue processing, LCA contained 4.5% of total radioactivity. After tissue processing, labeled water-soluble components were lost and 88% of the retained radioactivity was in the LCA pool. The enrichment of endogenous LCA radioactivity was attributable to the selective extraction of endogenous short-chain and free carnitine. Nearly 75% of endogenous LCA was preserved. In contrast, 99.5% of both endogenous short-chain and free carnitine were extracted. Thus, endogenous LCA can be selectively preserved, permitting quantitative subcellular localization of this amphiphile with ultrastructural autoradiography.

Identification of patients who do not require beta antagonists after myocardial infarction.

Recent results obtained from large clinical trials demonstrate that long-term administration of beta-adrenergic antagonists to patients following myocardial infarction reduces the incidence of death for as long as two years. Therefore, it has been recommended that, in the absence of contraindications, all patients be given beta antagonists after infarction. A review of the literature regarding prognosis after infarction demonstrates that patients who have had only one infarction and who have good ventricular function, no complex ectopy, no angina, and negative results of stress testing have a mortality rate no greater than 0.6 percent per year. For a person in this category, the probability that beta blockade will preclude death is exceedingly low (approximately 1 in 700). Both the commonly described side effects, as well as the recent observation that beta-adrenergic antagonists lower the concentration of serum high-density lipoproteins, potentially reducing the protection against atherosclerosis thought to be conferred by high-density lipoproteins, suggest that it may be unwise to use beta antagonists in patients who have a very low probability of benefit.

Fibronectin in rat heart: a link between cardiac myocytes and collagen.

Fibronectin, a glycoprotein that binds to collagen and modifies the adhesion properties and motility of cells in culture, is present in the interstitium of rat hearts. To localize fibronectin more precisely and to assess its relationship to the myocyte and to connective tissue elements, we employed a double antibody technique to label myocardial fibronectin with electron-dense ferritin to permit an ultrastructural analysis. Fibronectin was found to be associated with collagen, and in some cases appeared to link collagen fibers. Fibronectin was also found inserted along the surfaces of cardiac myocytes, connecting these cells to perimyocytic collagen. These ultrastructural relationships imply that fibronectin is a major component of the myocardial interstitium, and may affect myocardial compliance and control the motion of myocytes during the contraction and relaxation of the heart.

Cytosolic lysophospholipase in cardiac myocytes and its inhibition by L-palmitoyl carnitine.

Since lysophosphatides have been implicated as arrhythmogenic metabolites, modulation of their catabolism in cardiac myocytes has been characterized. Rat cardiac myocytes and mesenchymal cells grown in culture were found to contain cytosolic lysophospholipase with specific activities of 1.3 +/- 0.1 and 0.9 +/- 0.1 nmol X mg-1 X min-1, respectively. Rat myocytic lysophospholipase had a molecular mass of approximately 20,000 daltons, estimated by gel filtration chromatography. Kinetic analysis of cytosolic myocytic lysophospholipase demonstrated a Michaelis constant of 11 microM, a pH optimum of 8.0, and competitive inhibition by L-palmitoyl carnitine (inhibitory constant of 12 microM). Although lysophospholipase-transacylase activity could not be detected in rat myocyte or mesenchymal cell cultures, rabbit myocytes isolated by perfusion of isolated hearts with collagenase contained lysophospholipase-transacylase in cytosolic extracts with a specific activity of 0.2 nmol X mg-1 X min-1. These results demonstrate the presence of lysophospholipase in cardiac myocytes and suggest that the increase in long-chain acyl carnitine, which occurs during myocardial ischemia, may contribute to accumulation of lysophosphatides within cardiac myocytes.

Peripartum heart failure due to primary pulmonary hypertension.

Despite the high incidence of sudden death in pregnant patients with primary pulmonary hypertension (PPH) and heart failure, no data are available that thoroughly elucidate the peripartum hemodynamic alterations occurring in these patients. The present report describes the clinical course of a pregnant patient with PPH and provides data regarding peripartum hemodynamic alterations. Hemodynamic parameters were stable during labor and delivery, but pulmonary vascular resistance rose gradually while cardiac output fell after parturition. Dobutamine caused a modest but unsustained increase in cardiac output. Nitroprusside produced a significant sustained augmentation of cardiac output from 3.5 to 5.0 liters/min due to reduction of systemic and pulmonary vascular resistances, and permitted restoration of hemodynamic stability and resolution of heart failure. The authors believe that pregnant patients with PPH and severe heart failure in whom abortion is not possible should have complete hemodynamic monitoring during parturition and for several days thereafter. Segmental epidural anesthesia and lateral positioning of the patient minimize hemodynamic alterations during labor and delivery. Nitroprusside and dobutamine may be effective for treatment of congestive heart failure.

Lysophosphatidyl choline potentiates Ca2+ accumulation in rat cardiac myocytes.

Lysophosphoglycerides are amphiphilic phospholipids that accumulate in ischemic myocardium and elicit electrophysiological alterations in normoxic Purkinje fibers and ventricular muscle that are analogous to alterations characteristic of ischemic tissue in vivo and that are compatible with altered sarcolemmal permeability to divalent cations. To assess directly the potential influence of lysophosphoglycerides on calcium transport, we characterized changes in the accumulation of 45Ca2+ by cultured cardiac myocytes exposed to selected concentrations of lysophosphatidyl choline (LPC). Perfusion for 10 min with 80 microM LPC augmented the amount of 45Ca2+ in myocytes compared with that in control cells (5.1 +/- 0.7 vs. 2.8 +/- 0.26 nmols Ca2+/mg protein, respectively; P less than 0.005) but did not alter total cell calcium content measured by atomic absorption spectrometry (11.6 +/- 1.0 nmols/mg protein), suggesting equivalent augmentation of bidirectional Ca2+ flux by LPC. In contrast, perfusion for 15 min with 100 microM LPC not only augmented 45Ca2+ accumulation but also increased total cellular Ca2+ content, as the quantity of 45Ca2+ accumulated reached 16.9 +/- 1.4 nmols/mg protein, a value substantially exceeding the normal total Ca2+ content (P less than 0.0025 compared with control cells). In contrast to results observed after only a 5-min exposure to 100 microM LPC, Ca2+ accumulation induced by 15 min of perfusion was not precluded by verapamil (10(-8)M), could not be reversed by perfusion without LPC, and was associated with complete cessation of beating, markedly altered morphology, and substantial depletion of cellular creatine kinase activity. Thus LPC may not only contribute to malignant ventricular dysrhythmias but also may potentiate ischemic injury by facilitating calcium ingress.

Hydrolysis of phosphatidylethanolamine induced by nominally synthetic lysophosphoglycerides: methodological implications.

Synthetic lysophosphatidylethanolamine (LPE) obtained from commercial sources augmented the apparent activity of phospholipase A2 (PLA2) in cardiac mitochondrial and microsomal fractions. For elucidation of this phenomenon, 2-[1-14C]linoleylphosphatidylethanolamine was incubated in the absence of cell protein with selected concentrations of LPE, lysophosphatidylcholine (LPC), Ca2+, ionic and nonionic detergents, and phospholipids with functional groups similar to those of LPE. Hydrolysis of phosphatidylethanolamine (PE) was evaluated by measurement of 14C-labeled free fatty acid release and confirmed by quantification of [14C]ethanolamine-labeled LPE formed. The reaction was dependent on the concentrations of Ca2+, PE, and LPE, exceeding 1.5 nmol/h with 20 micro M LPE and 30 micro M PE. Hydrolysis occurred in the presence of as little as 1 micro M LPE. PE was not hydrolyzed by comparable concentrations of ionic or nonionic detergents or by several closely related phosphatides, including LPC. Purification of synthetic LPE by high-performance LC to remove contaminating PLA2 eliminated the effect. LPE-induced hydrolysis of PE was found to depend on contamination of the LPE by PLA2 from Crotalus atrox, employed in the commercial synthesis of the lysophosphatide from the precursor used, phosphatidylethanolamine. Contamination of commercially obtained lysophosphoglycerides by PLA2 constitutes a technical pitfall which may cloud interpretation of experiments performed with inadequately purified material.

Reduction of early ventricular arrhythmia by acebutolol in patients with acute myocardial infarction.

To assess the effects of intravenously administered acebutolol (1-20 mg every 4 hours for 24 hours) on cardiac rhythm and performance, we studied 72 patients with evolving myocardial infarction. Twenty-five patients were treated with acebutolol beginning 6 hours after the first increase in the level of plasma creatine kinase. Enzymatically estimated infarct size was compared with that of 25 controls matched for predicted infarct size. Observed infarct sizes were not significantly different in the 2 groups (37 +/- 5 and 30 +/- 5 CK-gram equivalents, respectively). Mean heart rate, diastolic blood pressure, and cardiac output declined from control values during treatment with acebutolol, but remained within the normal range. Mean pulmonary artery pressure and pulmonary artery occlusive pressure were unchanged. In a group of 22 treated patients matched with 22 control subjects for frequency of ventricular extrasystoles, acebutolol effected a prompt reduction in frequencies of ventricular extrasystoles and repetitive arrhythmias, whereas values were not significantly changed in controls during the corresponding intervals. Accordingly, acebutolol may be a useful antiarrhythmic agent in selected patients with acute myocardial infarction with adversely altering haemodynamic stability or enzymatically estimated infarct size.