Palmitylcarnitine inhibition of the calcium pump in cardiac sarcoplasmic reticulum: a possible role in myocardial ischemia

Long-Chain Acylcarnitines and Cardiac Excitation-Contraction Coupling: Links to Arrhythmias

A growing number of metabolomic studies have associated high circulating levels of the amphiphilic fatty acid metabolites, long-chain acylcarnitines (LCACs), with cardiovascular disease (CVD) risk. These studies show that plasma LCAC levels can be correlated with the stage and severity of CVD and with indices of cardiac hypertrophy and ventricular function. Complementing these recent clinical associations is an extensive body of basic research that stems mostly from the twentieth century. These works, performed in cardiomyocyte and multicellular preparations from animal and cell models, highlight stereotypical derangements in cardiac electrophysiology induced by exogenous LCAC treatment that promote arrhythmic muscle behavior. In many cases, this is coupled with acute inotropic modulation; however, whether LCACs increase or decrease contractility is inconclusive. Linked to the electromechanical alterations induced by LCAC exposure is an array of effects on cardiac excitation-contraction coupling mechanisms that overload the cardiomyocyte cytosol with Na⁺ and Ca²⁺ ions. The aim of this review is to revisit this age-old literature and collate it with recent findings to provide a pathophysiological context for the growing body of metabolomic association studies that link circulating LCACs with CVD.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Long-chain acylcarnitine induces Ca2+ efflux from the sarcoplasmic reticulum

Long-chain acylcarnitines increase intracellular Ca2+ (Ca2+i) and induce electrophysiologic alterations that likely contribute to the genesis of malignant ventricular arrhythmias induced during myocardial ischemia. The mechanisms by which long-chain acylcarnitines increase Ca2+i are not known, although it occurs in the presence of Ca2+ channel blockade and inhibition of Na+/Ca2+ exchange. Long-chain acylcarnitines activate Ca2+ release channels from skeletal muscle sarcoplasmic reticulum (SR), but their effect on cardiac SR is unclear. To test the hypothesis that long-chain acylcarnitines increase Ca2+i from the SR, SR-enriched membrane fractions were prepared from rabbit left ventricular myocardium using sucrose density-gradient centrifugation and characterized by marker enzyme analysis. 45Ca2+ efflux was assessed in the presence or absence of long-chain acylcarnitines. Palmitoylcarnitine and stearoylcarnitine produced concentration-dependent efflux of 45Ca2+, whereas shorter chain acylcarnitines, palmitate, and palmitoyl-coenzyme A did not. Pretreatment of cardiac SR vesicles with ryanodine did not prevent palmitoylcarnitine-induced Ca2+ release. In addition, palmitoylcarnitine did not influence specific [3H]ryanodine binding, suggesting a mechanism independent of alterations in ryanodine receptor/Ca2+ release channel binding. In summary, long-chain acylcarnitines enhance Ca2+ release from cardiac SR vesicles and may thereby mobilize Ca2+i to induce electrophysiologic derangements under conditions, such as ischemia, in which these amphiphiles accumulate.

Carnitine and its derivatives in cardiovascular disease

Carnitine and its derivative propionyl-L-carnitine are endogenous cofactors which enhance carbohydrate metabolism and reduce the intracellular buildup of toxic metabolites in ischemic conditions. The carnitines have been, and are being used in a spectrum of diseases including multiple cardiovascular conditions. These include angina, acute myocardial infarction, postmyocardial infarction, congestive heart failure, peripheral vascular disease, dyslipidemia, and diabetes. Most published data on carnitine, propionyl-L-carnitine, and other carnitine congeners are favorable but the clinical trials have been relatively small. In currently used doses, these substances are virtually devoid of significant side effects.

Aspects of calcium-activated chloride currents: a neuronal perspective

Ca(2+)-activated Cl- channels are expressed in a variety of cell types, including central and peripheral neurones. These channels are activated by a rise in intracellular Ca2+ close to the cell membrane. This can be evoked by cellular events such as Ca2+ entry through voltage- and ligandgated channels or release of Ca2+ from intracellular stores. Additionally, these Ca(2+)-activated Cl currents (ICl(Ca)) can be activated by raising intracellular Ca2+ through artificial experimental procedures such as intracellular photorelease of Ca2+ from "caged" photolabile compounds (e.g. DM-nitrophen) or by treating cells with Ca2+ ionophores. The potential changes that result from activation of Ca(2+)-activated Cl- channels are dependent on resting membrane potential and the equilibrium potential for Cl-. Ca2+ entry during a single action potential is sufficient to produce substantial after potentials, suggesting that the activity of these Cl- channels can have profound effects on cell excitability. The whole cell ICl(Ca) can be identified by sensitivity to increased Ca2+ buffering capacity of the cell, anion substitution studies and reversal potential measurements, as well as by the actions of Cl- channel blockers. In cultured sensory neurones, there is evidence that the ICl(Ca) deactivates as Ca2+ is buffered or removed from the intracellular environment. To date, there is no evidence in mammalian neurones to suggest these Ca(2+)-sensitive Cl- channels undergo a process of inactivation. Therefore, ICl(Ca) can be used as a physiological index of intracellular Ca2+ close to the cell membrane. The ICl(Ca) has been shown to be activated or prolonged as a result of metabolic stress, as well as by drugs that disturb intracellular Ca2+ homeostatic mechanisms or release Ca2+ from intracellular stores. In addition to sensitivity to classic Cl- channel blockers such as niflumic acid, derivatives of stilbene (4,4'diisothiocyanostilbene-2,2'-disulphonic acid, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid) and benzoic acid (5-nitro 2-(3-phenylpropylamino) benzoic acid), ICl(Ca) are also sensitive to polyamine spider toxins and some of their analogues, particularly those containing the amino acid residue arginine. The physiological role of Ca(2+)-activated Cl- channels in neurones remains to be fully determined. The wide distribution of these channels in the nervous system, and their capacity to underlie a variety of events such as sustained or transient depolarization or hyperpolarizations in response to changes in intracellular Ca2+ and variations in intracellular Cl- concentration, suggest the roles may be subtle, but important.

Cardioprotective effect of L-carnitine in rats submitted to permanent left coronary artery ligation

Several studies have suggested that L-carnitine may limit the cellular alterations induced by myocardial hypoxia or ischemia. In the present study, rats were subjected to chronic treatment with L-carnitine (0, 25, 50 or 200 mg/kg/day i.p.) for 9 days prior to being submitted to permanent regional myocardial ischemia by left coronary artery ligation in situ. Following 48 hours of coronary occlusion, infarct size was measured using planimetry of transverse sections of the hearts, which had been stained with nitro-blue tetrazolium. Various functional and metabolic parameters have also been measured in isolated perfused hearts. Treatment with L-carnitine at 200 mg/kg/day i.p. for 9 days led to a significant reduction in infarct size and a better preservation of residual cardiac function. However, none of the metabolic parameters measured were modified. In conclusion, we suggest that the preservation of cardiac contractile function observed with L-carnitine pretreatment is secondary to carnitine-induced infarct size limitation.

Differential mechanism of block of palmitoyl lysophosphatidylcholine and of palmitoylcarnitine on inward rectifier K+ channels of guinea-pig ventricular myocytes

We investigated the effect of lysophosphatidylcholine (lysoPtdCho) and palmitoylcarnitine (PamCar), ischemia-induced amphipathic lipid metabolites, on the inward rectifier K+ channel in guinea-pig ventricular cells, under whole-cell and cell-attached configurations with patch-clamp techniques. (a) Both lysoPtdCho (10-50 microM) and PamCar (10-50 microM) depolarized the resting membrane potential (RP), retarded the repolarization of action potential, provoked spontaneous action potential discharges from oscillatory afterpotentials, and eventually caused a sudden rise of the RP to plateau levels. (b) These lysoPtdCho- or PamCar-induced depolarizations of RP were due to a decrease in the inward rectifier K+ current (IK1), and the sudden rise of the RP could be accounted for by a crossover of N-shaped current-voltage relationship on the voltage axis (zero current line) more than once. (c) Single-channel studies in the cell-attached mode revealed that lysoPtdCho (5-100 microM) decreased the conductance of the single IK1 channel with little change in its open probability, whereas PamCar (10-50 microM) did so by decreasing the open probability, with the channel conductance unaltered. (d) A short-chain acylcarnitine, l-propionylcarnitine (PpCar, 100 microM), prevented the depressant effect of lysoPtdCho (50 microM), but not of PamCar (50 microM), on the IK1. (e) Both lysoPtdCho and PamCar produced identical electrophysiological alterations on the membrane potential and IK1 in whole-cell recordings. However, molecular mechanisms involved in the effects of these toxic metabolites on single IK1 channels differ.

Recent insights pertaining to sarcolemmal phospholipid alterations underlying arrhythmogenesis in the ischemic heart

Myocardial ischemia in vivo is associated with dramatic electrophysiologic alterations that occur within minutes of cessation of coronary flow and are rapidly reversible with reperfusion. This suggests that subtle and reversible biochemical alterations within or near the sarcolemma may contribute to the electrophysiologic derangements. Our studies have concentrated on two amphipathic metabolites, long-chain acylcarnitines and lysophosphatidylcholine (LPC), which have been shown to increase rapidly in ischemic tissue in vivo and to elicit electrophysiologic derangements in normoxic tissue in vitro. Incorporation of these amphiphiles into the sarcolemma at concentrations of 1 to 2 mole%, elicits profound electrophysiologic derangements analogous to those observed in ischemic myocardium in vivo. The pathophysiological effects of the accumulation of these amphiphiles are thought to be mediated by alterations in the biophysical properties of the sarcolemmal membrane, although there is a possibility of a direct effect upon ion channels. Inhibition of carnitine acyltransferase I (CAT-I) in the ischemic cat heart was found to prevent the increase in long-chain acylcarnitines and LPC and to significantly reduce the incidence of malignant arrhythmias including ventricular tachycardia and fibrillation. This review focuses on the electrophysiologic derangements that are observed during early ischemia and presents data supporting the concept that accumulation of these amphiphiles within the sarcolemma contributes to these changes. The potential contribution of these amphiphiles to the increases in extracellular potassium and intracellular calcium are examined. Finally, recent data pertaining to the accumulation of long-chain acylcarnitines on cell-to-cell uncoupling are presented. In addition to the events reviewed here, there are many other alterations that occur during early myocardial ischemia, but the results from multiple studies over the past two decades indicate that the accumulation of these amphiphiles contributes importantly to arrhythmogenesis and that development of specific inhibitors of CAT-I or phospholipase A2 may be a promising therapeutic strategy to attenuate the incidence of lethal arrhythmias associated with ischemic heart disease in man.

Arachidonic acid-induced Ca2+ release from isolated sarcoplasmic reticulum

Arachidonic acid has been shown to release Ca2+ from isolated skeletal and cardiac sarcoplasmic reticulum (SR) vesicles. The release took place nearly equally well from all fractions of the SR and was only partially inhibited by ruthenium red, suggesting that some other pathway is involved in addition to the SR Ca2+ release channel. Arachidonic acid increased SR Ca2+ efflux even in the presence of several different SR Ca2+ pump inhibitors. It also had considerably less effect on uptake measured in the presence of oxalate and did not appear to inhibit Ca(2+)-dependent ATPase activity. Thus, the SR Ca2+ pump also appears to be minimally perturbed by arachidonic acid. Arachidonyl CoA was more effective at releasing Ca2+ than the parent compound. Arachidonic acid effects were not inhibited by lipoxygenase or cyclooxygenase inhibitors, suggesting that no eicosanoids are involved in the effects under study here. Flunarizine, cinnarizine and propyl-methylenedioxyindene inhibited the Ca2+ release induced by arachidonic acid. The effects of arachidonic acid appear to depend on the ratio of arachidonic acid to membrane vesicles.

Palmitoyl-DL-carnitine has calcium-dependent effects on cultured neurones from rat dorsal root ganglia

1. The effects of palmitoyl-DL-carnitine (0.01 to 1 mM) on whole cell voltage-activated calcium channel currents carried by calcium or barium and Ca(2+)-activated chloride currents were studied in cultured neurones from rat dorsal root ganglia. 2. Palmitoyl-DL-carnitine applied to the extracellular environment or intracellularly via the patch solution reduced Ca2+ currents activated over a wide voltage range from a holding potential of -90 mV. Inhibition of high voltage activated Ca2+ channel currents was dependent on intracellular Ca2+ buffering and was reduced by increasing the EGTA concentration from 2 to 10 mM in the patch solution. Barium currents were significantly less sensitive to palmitoyl-DL-carnitine than Ca2+ currents. 3. The amplitude of Ca(2+)-activated Cl- tail currents was reduced by palmitoyl-DL-carnitine. However, the duration of these Cl- currents was greatly prolonged by palmitoyl-DL-carnitine, suggesting slower removal of free Ca2+ from the cytoplasm following Ca2+ entry through voltage-activated channels. 4. Palmitoyl-DL-carnitine evoked Ca(2+)-dependent inward currents which could be promoted by activation of the residual voltage-activated Ca2+ currents and attenuated by intracellular application of EGTA. 5. We conclude that palmitoyl-DL-carnitine reduced the efficiency of intracellular Ca2+ handling in cultured dorsal root ganglion neurones and resulted in enhancement of Ca(2+)-dependent events including inactivation of voltage-activated Ca2+ currents. The activation of inward currents by palmitolyl-DL-carnitine may involve Ca(2+)-induced Ca2+ release from intracellular stores, or direct interaction of palmitoyl-DL-carnitine with Ca2+ stores.

Role of fatty acid metabolites in the development of myocardial ischemic damage

1. The review deals with possible mechanisms by which fatty acids amplify ischemic damage in myocardium. 2. The accumulation of free fatty acids, long chain acyl CoA and carnitine esters during hypoxia and their effects on various enzymatic systems are discussed. 3. Findings on the influence of exogenous fatty acids as well as observations concerning an inhibition of fatty acid degradation are also considered. 4. Finally the role of an oxygen steal effect, as an indirect mechanism for the fatty acid induced amplification of ischemic damage, is discussed.

Inhibitory effects of palmitoylcarnitine and lysophosphatidylcholine on the sodium current of cardiac ventricular cells

We investigated the effects of ischemia-related amphipathic compounds, palmitoylcarnitine (PamCar, 0.5-50 microM) and lysophosphatidylcholine (lysoPtdCho, 5-50 microM) on sodium current (INa) of guinea-pig ventricular myocytes. The cells were perfused with low-Na+ (60 mM) Tyrode's solution, and Ca2+ and K+ currents were blocked by external Co2+ (3 mM) and internal Cs+ (140 mM), respectively. INa was elicited by depolarizing voltage steps from a holding potential of -100 mV at a temperature of 33 degrees C. PamCar (5 microM) decreased the peak INa (attained at -20 mV or -30 mV) from 6.1 +/- 2.1 nA to 3.9 +/- 1.4 nA (n = 11), or by 36.1% within 2 min, and shifted the curve of steady-state INa inactivation by 5.4 mV in the positive direction (from -76.3 +/- 4.6 mV, control to -70.9 +/- 4.0 mV, in PamCar, n = 4). Partial restoration of the amplitude and the shift of the steady-state inactivation curve of INa was attained after washout of PamCar. In contrast, lysoPtdCho at concentrations over 10 microM irreversibly depressed the INa within 0.5-3 min and the reduction of INa was followed by cell contracture or cell death (n = 9). The survival time, defined as a period from the start of lysoPtdCho application to the time of the last successful recording of the INa (before evolution of sudden changes in the holding current), depended on the concentrations of lysoPtdCho. Both PamCar and lysoPtdCho retarded the time course of activation and inactivation of INa.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acids suppress recovery of heart function after hypothermic perfusion

Working rat hearts were perfused for 15 minutes at 37 degrees C before switching to a Langendorff perfusion (60 mm Hg aortic pressure) at 10 degrees C for 40 minutes of hypothermic arrest. Ventricular function was allowed to recover for 15 minutes at 37 degrees C by reestablishing the prehypothermic conditions. The perfusate was Krebs-Henseleit bicarbonate buffer containing 3% bovine serum albumin and either glucose (11 mmol/L) or glucose (11 mmol/L) plus palmitate (1.2 mmol/L) and gassed with 95% O2 and 5% CO2. In hearts receiving glucose alone as substrate, coronary flow was maintained constant during the 40 minutes of hypothermic arrest and returned to prehypothermic rates with rewarming. Ventricular function, as estimated by peak systolic pressure and heart rate, recovered to the prehypothermic level. When palmitate was added, coronary flow decreased continuously throughout the hypothermic perfusion (22% decrease by 40 minutes), and ventricular pressure development was lower throughout the rewarming perfusion. Tissue levels of adenosine triphosphate and creatine phosphate were well maintained and long-chain acyl coenzyme A and acyl carnitine decreased during hypothermia regardless of the substrate provided. With rewarming, tissue levels of adenosine triphosphate and creatine phosphate decreased in those hearts receiving palmitate. Omission of fatty acid either during hypothermia or during the first 5 minutes of rewarming improved recovery of function. Addition of oxfenicine to inhibit fatty acid oxidation, or inhibition of Ca2+ overload by verapamil and low perfusate Ca2+, prevented the effects of palmitate on ventricular function.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of calcium release from sarcoplasmic reticulum

Calcium release from sarcoplasmic reticulum (SR) has been elicited in response to additions of many different agents. Activators of Ca2+ release are here tentatively classified as activators of a Ca2+-induced Ca2+ release channel preferentially localized in SR terminal or as likely activators of other Ca2+ efflux pathways. Some of these pathways may be associated with several different mechanisms for SR Ca2+ release that have been postulated previously. Studies of various inhibitors of excitation-contraction coupling and of certain forms of SR Ca2+ release are summarized. The sensitivity of isolated SR to certain agents is unusually affected by experimental conditions. These effects can seriously undermine attempts to anticipate effects of the same pharmacological agents in situ. Finally, mention is made of a new preparation ("sarcoballs") designed to make the pharmacological study of SR Ca2+ release more accessible to electrophysiologists, and some concluding speculations on the future of SR pharmacology are offered.

Effects of L-propionylcarnitine on electrical and mechanical alterations induced by amphiphilic lipids in isolated guinea pig ventricular muscle

We examined the effects of L-propionylcarnitine (Prop. C), a short-chain acylcarnitine, on amphiphile (L-lysophosphatidylcholine or L-palmitoylcarnitine)-induced electrophysiological and ultrastructural changes in isolated guinea pig ventricular papillary muscles, under acidic conditions (pH 6.9). Conventional microelectrode, tension-recording, and electron microscope techniques were used. Both amphiphiles, at a concentration of 10(-4) M, significantly decreased the resting membrane potential, action potential amplitude, and action potential duration, but increased the developed and resting tension. Such amphiphile-induced electrical changes were not observed in muscles pretreated with the beta-blocker, atenolol, although the mechanical changes remained unaffected. The application of Prop. C (10(-2) M), in the continued presence of the amphiphiles caused a return of the action potential duration and the developed tension to the control level. However, the resting potential and action potential amplitude remained unaffected; in fact, the maximum upstroke velocity (Vmax) of the action potential tended to decrease further. Pretreatment with Prop. C prevented all the amphiphile-induced electrophysiological and mechanical changes, except for Vmax. Electron microscopic studies revealed that amphiphile-induced ultrastructural changes were prevented, at least in part, in the presence of Prop. C. Thus, Prop. C antagonizes some of deleterious effects of amphiphiles, such as lysophosphatidylcholine and palmitoylcarnitine, upon the electrical and mechanical activities of the ventricular muscle, under acidic conditions.

Palmitoyl carnitine: an endogenous promotor of calcium efflux from rat heart mitochondria

The effects of the fatty acid ester palmitoyl carnitine (PC) on mitochondrial Ca2+ handling and ATP synthesis are described. At low concentrations (5-40 microM) PC was found to produce changes in mitochondrial Ca2+ handling, the most significant effect (P less than 0.05) being the promotion of Ca2+ efflux (EC25 = 1.19 +/- 0.11 microM). Studies on mitochondrial substrate oxidation in the presence of either glutamate plus malate, or succinate, confirmed the ability of PC (10-100 microM) to cause loss of respiratory control as shown by reductions in the Respiratory Control Index for each substrate. It was concluded that the effect of PC on Ca2+ transport was due to a direct action on the Na+-Ca2+ antiporter system, whilst the effect on respiration was due to an uncoupling action.

Antagonists and activators at calcium channels. Effects in the gastrointestinal tract

Most calcium antagonists have relatively minor effects in the gastrointestinal (GI) tract; the factors influencing drug selectivity are reviewed. Voltage-dependent Ca channels (VOCs) in GI smooth muscle appear to be essentially similar to those in the cardiovascular system in their sensitivity to calcium antagonists. However, selective conditions for channel activation may allow antagonists to be selective in certain disease conditions. Indirect effects on blood flow may be crucial to certain parameters (e.g., acid secretion). Activators of VOCs have similar effects in vascular and GI smooth muscle. Some endogenous activators of VOCs may exist and evidence for control of VOC activity by lipid metabolites is indicated. Acyl carnitines may function as endogenous activators of VOCs.

Differential effects of L-propionylcarnitine on the electrical and mechanical properties of guinea pig ventricular muscle in normal and acidic conditions

We studied the effects of L-propionylcarnitine (PC) on transmembrane action potentials and isometric contractile tension in isolated guinea pig ventricular papillary muscles. The effects of 5 concentrations of PC (10(-5), 10(-4), 10(-3), 10(-2) and 3 X 10(-2)M) were examined in both normal (pH 7.4) and acidic (pH 6.9) conditions. The concentrations of 10(-5) to 10(-2)M had no significant effect on action potential amplitude, maximum upstroke velocity of phase 0 and resting potential, in either condition. At pH 7.4, action potential duration (ADP) was significantly (P less than 0.05) or insignificantly shortened by the drug depending upon the concentration used. At pH 6.9, however, the APD was prolonged by moderate PC concentrations (10(-3) and 10(-2)M), in which the effective refractory period (ERP) was also lengthened, associated with an increased ERP/APD ratio. In both pH conditions, the highest concentration (3 X 10(-2)M) significantly (P less than 0.05) decreased all these action potential parameters. PC had a biphasic effect on the developed tension. In both pH conditions, low PC concentrations (10(-5) to 10(-3)M) produced an initial augmentation of the contraction, followed by subsequent reduction. The initial augmentation disappeared by pretreatment with reserpine or propranolol, suggesting the involvement of beta-adrenoceptors. In the steady state, all PC concentrations produced a negative inotropic effect at pH 7.4, while at pH 6.9 only high concentrations (10(-2)M and 3 X 10(-2)M) had this effect. These results suggest that the effects of PC in an acidic condition differ considerably from those in a normal pH condition and that limited concentrations of PC (10(-3) to 10(-2)M) may prevent re-entrant arrhythmias from developing under acidic conditions via lengthening of the ERP, without deleterious effects on the contractile force.

Direct activation of Ca2+ channels by palmitoyl carnitine, a putative endogenous ligand

1 Palmitoyl carnitine, a lipid metabolite which accumulates in cytoplasmic membranes during ischaemia, has been shown to resemble the Ca2+ channel activator, Bay K 8644, in K+-depolarized smooth muscle. Palmitoyl carnitine caused concentration-dependent (1-1000 mumol l-1) augmentations in the sensitivity to Ca2+ of K+-depolarized taenia preparations from the guinea-pig caecum. The (+/-)-isomer was equieffective with the (-)-isomer, whereas carnitine was ineffective and palmitic acid relaxed the tissues. The shift to the left of Ca2+ concentration-response curves induced by palmitoyl carnitine (100 mumol l-1) was additive with that of Bay K 8644 (1 mumol l-1). 2 The interactions of palmitoyl carnitine with the different classes of calcium-antagonist were similar to those seen with Bay K 8644. Schild plots of the calcium-antagonist effects of nifedipine were shifted to the right following preincubation of the taenia with palmitoyl carnitine (30-300 mumol l-1). The inhibitory effects of verapamil were especially sensitive to palmitoyl carnitine (100 mumol l-1). Whereas the potency of diltiazem as a calcium-antagonist was reduced by palmitoyl carnitine (100 mumol l-1), the inhibitory effects of the lipophilic class III calcium-antagonists, cinnarizine and flunarizine, were entirely resistant to palmitoyl carnitine (100 mumol l-1). 3 Although palmitoyl carnitine has detergent properties in high concentrations and lyses red blood cells, these effects were not Ca2+-dependent, nor were they modified by calcium-antagonists. Other detergents did not have selective interactions with Ca2+ channels. 4 Palmitoyl carnitine inhibited [3H]-nitrendipine, [3H]-verapamil and [3H]-diltiazem binding to rat cortical membranes with IC50 values (mumol l-1) of 120 +/- 1, 95 +/- 17 and 120 +/- 15 mumol l-1 respectively. The inhibition showed little temperature-dependence, in contrast to that of Bay K 8644, except for a small reduction in the IC50 value for [3H]-verapamil binding at 37 degrees C (42 +/- 5 mumol l-1). Palmitoyl carnitine interacted selectively with the Ca2+ channel, in that effects on ligand binding to alpha-adrenoceptors, beta-adrenoceptors and 5-HT1A receptors occurred only at 5-10 fold higher concentrations. 5 It is concluded that palmitoyl carnitine, at concentrations which have previously been shown to occur in the cytoplasm during myocardial ischaemia, may interact directly with Ca2+ channels and may therefore be considered as an endogenous modulator of channel function. The site of action differs from that of other agents.

Effects of long-chain fatty-acyl esters of coenzyme A and carnitine on cell-free rat heart preparations

The purpose of this study was to investigate the effects of fatty acyl CoA and carnitine esters on the glycolytic system of the rat heart. Using a respiring incubation mixture containing a whole-heart homogenate it was observed that oleoyl-CoA slowed down the glucose disappearance whereas lactate accumulation did not change. Experiments were also performed by means of an incubation mixture prepared with a soluble heart extract, considered to contain all glycolytic enzymes present in heart fibres. Palmitoyl-CoA or oleoyl-CoA as well as palmitoyl carnitine, added separately or together, were unable to alter the glucose disappearance and lactate accumulation in this mixture. These data suggest that long chain acyl-esters have not direct inhibitory actions on the heart glycolytic activity. However, CoA esters seem to exert indirect inhibitory effects which may be relevant to the myocardium under oxygen restriction situations.

Separation and characteristics of inside-out and right side-out vesicles from a rat cardiac sarcolemma preparation

Purified cardiac sarcolemma (SL) vesicles are highly suitable to study various Ca2+-transport systems present in the SL. We describe in this paper the separation of the Inside-Out (IO) and Right side-Out (RO) oriented vesicle subpopulations from a purified rat heart SL preparation. The isolated subfractions were characterized with respect to the number of beta-adrenergic binding sites and the Ca2+-uptake and (Ca2+-Mg2+)-ATPase activities. It was found that the Ca2+-uptake and the (Ca2+-Mg2+)-ATPase activities reside in the IO fraction and are virtually absent in the RO fraction, confirming that the active Ca2+-uptake represents the outward directed sarcolemmal Ca2+-flux.

Diabetes-induced abnormalities in the myocardium

One of the leading causes of mortality in diabetics is myocardial disease. In the past few years this subject has generated a significant amount of interest with the result that myocardial problems associated with diabetes are far better understood. Though originally thought to occur as a result of atherosclerosis, various studies have shown that heart disease can occur in the absence of atherosclerosis, suggesting a diabetic cardiomyopathy. Using diabetic animals, it has been possible to characterize diabetes-induced myocardial abnormalities. Diabetic rat hearts do not respond to conditions of high stress as well as controls. The functional depression is accompanied by altered cardiac enzyme systems. A decrease in myosin ATPase activity which appears to be a result of diabetes-induced hypothyroidism is seen. Also, a depression of sarcoplasmic reticular calcium ATPase, along with a depression of calcium uptake by the SR, is seen in diabetic rat hearts. Na+, K+ ATPase activity has also been shown to be depressed and the depression appears to correlate with depressed atrial contractility. High levels of circulating fats in diabetics may alter the integrity of membranes leading to altered enzyme activities. Insulin treatment has been relatively successful at reversing or preventing myocardial changes in the diabetic rat. Other treatments that have been studied include thyroid hormone treatment, since the depression of myosin ATPase can be corrected by such treatment; and carnitine treatment, as the elevation of long chain acyl carnitines (LCAC) and the resulting depression of calcium uptake in the SR can be so normalized. These treatments have not been successful at normalizing cardiac function. A combination of the two treatments normalized function only partially, suggesting that factors besides myosin ATPase and SR calcium uptake are involved. Other treatments that have been tried include vanadate, methyl palmoxirate, and choline and methionine. Vanadate treatment has proved to be encouraging in that it normalizes both function and hyperglycemia. Methyl palmoxirate, a fatty acid analog, normalized only the elevation of LCAC but did not affect function. Methionine and choline were only partially successful in preventing the functional alterations of diabetic rat hearts. The purpose of the present article is to review our understanding of diabetes-induced myocardial problems and their possible causes. Findings from our laboratory and others are described in which attempts have been made to normalize cardiac function.

The dependence of electrophysiological derangements on accumulation of endogenous long-chain acyl carnitine in hypoxic neonatal rat myocytes

To determine whether accumulation of long-chain acyl carnitine contributes to electrophysiological abnormalities induced by hypoxia, we characterized effects of normoxic and hypoxic perfusion on the subcellular distribution of endogenous long-chain acyl carnitine and transmembrane potentials of cultured rat neonatal myocytes. Hypoxia increased long-chain acyl carnitine more than 5-fold. Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (10 microM), a carnitine acyltransferase inhibitor, precluded accumulation of long-chain acyl carnitine induced by hypoxia. Tissue was processed for electron microscopy by a procedure specifically developed for selective extraction of endogenous short-chain and free carnitine but retention of endogenous long-chain acyl carnitine. In normoxic-perfused cells, long-chain acyl carnitine was concentrated in mitochondria and cytoplasmic membranous components. Only small amounts were present in sarcolemma. Hypoxia increased mitochondrial long-chain acyl carnitine by 10-fold and sarcolemmal long-chain acyl carnitine by 70-fold. After 60 minutes of hypoxia, sarcolemma contained 1.4 X 10(7) long-chain acyl carnitine molecules/micron 3 of membrane volume, a value corresponding to approximately 3.5% of total sarcolemmal phospholipid. Hypoxia also significantly decreased maximum diastolic potential, action potential amplitude and maximum upstroke velocity of phase 0. Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate inhibited accumulation of long-chain acyl carnitine in each subcellular compartment and prevented the depression of electrophysiological function induced by hypoxia. These results strongly implicate endogenous long-chain acyl carnitine as a mediator of electrophysiological alterations induced by hypoxia.

Effect of l-carnitine chloride and its acetyl derivative on the electrophysiological derangement induced by palmityl-l-carnitine in isolated canine ventricular muscle

Using the microelectrode technique, the effects of l-carnitine (LC) and acetyl-l-carnitine (ALC) on the changes in the transmembrane action potential of the canine ventricular muscle induced by palmityl-l-carnitine (PLC) were studied in comparison with those of disopyramide (D). LC (5 X 10(-3) M) itself had no effect on the electrophysiological parameters of the ventricular muscle. ALC (5 X 10(-3) M) increased the maximum rate of rise (dV/dt max) slightly and decreased the action potential duration (APD), although these changes were not statistically significant. D (1.5 X 10(-3) M) decreased dV/dt max and prolonged APD and the absolute refractory period (ARP). PLC (3 X 10(-4) M) decreased the resting membrane potential, action potential amplitude and dV/dt max, and it shortened APD and ARP. LC and ALC (5 X 10(-3) M) improved the electrophysiological derangement produced by PLC to the same degree. On the other hand, application of D (1.5 X 10(-5) M) resulted in no improvement of the electrophysiological derangement produced by PLC.

Reversible, highly localized alterations in fatty acid metabolism in the chronically ischemic canine myocardium

Acute myocardial ischemia is accompanied by a marked decrease in the oxidation of fatty acids. Whether similar changes occur during chronic ischemia was studied in 13 beagles. In 10 dogs, an ameroid constrictor was implanted about the left circumflex artery; 3 others served as sham-operated controls. Mitochondrial and peroxisomal fatty acid oxidation of (1-14C)oleate were measured and compared in affected (posterobasal left ventricular endocardial [posterior LV endo]) and unaffected (anteroapical LV epicardial [anterior LV epi]) tissues of control and experimental dogs. Five experimental and 3 control dogs were killed after 3 weeks. The posterior LV endo sections of experimental dogs at 3 weeks showed increased fatty acid oxidation due to peroxisomal (KCN-insensitive) beta oxidation (p less than 0.01). The anterior LV epi sections showed no difference in fatty acid oxidation between sham-operated and experimental dogs. Five dogs were studied after 3 months; fatty acid oxidation of the posterior LV endo section was normal. Thus, under a slowly evolving state of myocardial ischemia, highly localized and reversible adaptive changes in fatty acid oxidation occur that enable the affected tissue to cope with a fatty acid load. When collateralization is accomplished, fatty acid metabolism reverts to normal.

The effect of lipid intermediates on Ca2+ and Na+ permeability and (Na+ + K+)-ATPase of cardiac sarcolemma. A possible role in myocardial ischemia

The effect of fatty acid and acylcarnitine on Ca2+ and Na+ transporting enzymes and carriers was studied in sealed cardiac sarcolemma vesicles of mixed polarity. Palmitoylcarnitine markedly reduced the Na+ gradient-induced Ca2+ uptake. Half-maximal reduction was obtained at 15 microM of the carnitine derivative. In a same concentration range palmitoylcarnitine caused a rapid release of accumulated Ca2+ when added to Ca2+-filled vesicles, which suggests that palmitoylcarnitine increases the permeability of the sarcolemma vesicles to Ca2+. A rapid release of Ca2+ was also observed if Ca2+ was taken up by action of the Ca2+ pump. The (Ca2+ + Mg2+)-ATPase, which most likely drives this active Ca2+ uptake, was 90% increased by 50 microM palmitoylcarnitine and evidence was presented that the acylcarnitine effect again was linked to an alteration of Ca2+ permeability of the vesicles. At the same concentration acylcarnitine was not able to unmask the latent protein kinase, so that probably the sarcolemma ATP permeability was not affected. Palmitoylcarnitine at 25 microM did not affect the ouabain-sensitive (Na+ + K+) -ATPase in native sarcolemma vesicles, however, it inhibited markedly if the enzyme was measured in SDS-treated vesicles. The effect of increased free fatty acid concentration on some of the sarcolemma transporting properties was tested by adding oleate-albumin complexes with different molar ratios to the sarcolemma vesicles. In contrast to molar ratios 1 and 5, the ratio of 7 was able to induce a rapid Ca2+ release and to inhibit (Na+ + K+)-ATPase in either native or SDS-treated vesicles markedly. 22Na release from 22Na-preloaded sarcolemma vesicles was shown to be stimulated by either palmitoylcarnitine (50 microM) or oleate-albumin complex (with a molar ratio of 7). The possible significance of the observed effects of lipid intermediates on ion permeability and (Na+ + K+)-ATPase activity in isolated sarcolemma vesicles for the derangement of cardiac cell function in ischemia is discussed.

Acyl-carnitine effects on isolated cardiac mitochondria and erythrocytes

The effects of various long-chain acyl-carnitines (AC) on mitochondrial functions and red cell membrane stability were studied. Lower concentrations slightly stimulate respiration-dependent functions such as phosphorylation rate and Ca++ uptake velocity, whereas higher concentrations inhibit these functions with concomitant depression of the ATP/O ratio. The order of effectiveness among the AC is very similar for different mitochondrial functions. The differences among AC in their actions on red cell stability in hypotonic media and their differences in influence on mitochondrial functions exhibit less resemblance. The relative order of erythrolytic concentrations of AC follows the order of their critical micellar concentrations. Model calculations indicate that the concentrations of AC found in ischemic hearts are below those which exhibit inhibitory effects in vitro. Ultrastructural changes in mitochondria incubated with AC are different from those found in ischemic tissue. From this, it seems questionable whether the elevated AC levels in ischemic hearts are indeed as important for the development of membrane damage as is often supposed.

Depression of calcium transport in sarcoplasmic reticulum from diabetic rats: lack of involvement by specific regulatory mediators

Cardiac sarcoplasmic reticulum (SR) ATP-dependent Ca2+-uptake was found to be depressed in 4 month streptozotocin-induced diabetic rats. Calmodulin, cAMP-dependent protein kinase and K+ stimulated Ca2+-uptake to similar degrees in SR from both control diabetic rats. Long chain acylcarnitine (7 microM) decreased Ca2+-transport in control rats by 46% but only 26% in diabetic animals. The data suggests that the depression in cardiac SR Ca2+-uptake activity in diabetic rats is non-specific in origin and not a result of alterations in regulation of SR function.

Fatty acylcarnitine accumulation and membrane injury in ischemic canine myocardium

Although previous work has shown that long chain fatty acylcarnitine derivatives accumulate in ischemic canine myocardium, their role in the production of irreversible injury and associated sarcolemmal membrane injury is undefined. The present study examines the temporal and topographic relationship of the accumulation of long chain acylcarnitine with the uptake of technetium pyrophosphate and tissue calcium content during ligation of the left anterior descending coronary artery (LAD) in canine myocardium. After 60 minutes of fixed LAD ligation, there was no significant increase in long chain acylcarnitine content in the ischemic subendocardium compared with the corresponding nonischemic value. However, the ischemic subendocardium was irreversibly injured at this time, as assessed by a 4-fold increase in tissue calcium content and a 20-fold increase in technetium-99m pyrophosphate uptake after reperfusion. The ischemic subepicardium showed a 41% increase in long chain acylcarnitine content compared with the corresponding nonischemic subepicardium. However, the ischemic subepicardium contained only 50% of the calcium content and 10% of the technetium-99m pyrophosphate uptake found in the ischemic subendocardium. It is concluded that increases in fatty acylcarnitine can be dissociated from the development of irreversible ischemic injury during fixed LAD occlusion in ischemic canine myocardium.

L-palmitylcarnitine and calcium ions act similarly on excitatory ionic currents in avian ventricular muscle

Palmitylcarnitine, an amphiphile that accumulates in and leaks from ischemic heart tissue, affected the fast sodium ion channel and the slow calcium channel in avian ventricular muscle. In the presence of 5.4 mM external potassium ion, palmitylcarnitine reduced the maximum rate of rise of the action potential and increased action potential duration at the plateau level without changing the resting potential. Steady state inactivation of the maximum rate of rise, an index of fast sodium ion current, was shifted by 3-6 mV to more positive potentials by palmitylcarnitine. Elevation of external calcium ion to 5.4 mM (normal = 1.8 mM), like palmitylcarnitine, reduced the maximum rate of rise and shifted the voltage at which the action potential was half maximum by 3 mV to more positive potentials without changing the resting potential. Elevated external calcium ion, unlike palmitylcarnitine, reduced the duration of action potentials initiated from a resting potential of -80 mV. Palmitylcarnitine and elevated external calcium ion increased the amplitude, the maximum rate of rise, and duration of calcium ion dependent action potentials recorded in the presence of 25 mM [K+]0 that completely inactivated the fast sodium ion channel. Steady state inactivation of the maximum rate of rise of calcium-dependent action potentials was consistently shifted to more positive potentials by palmitylcarnitine (3 mV) and by elevated external calcium ion (6 mV) when the initial external calcium ion was 0.9 mM. Palmitylcarnitine, like elevated calcium, evoked a positive inotropic effect in the presence of propranolol. The similarity of the effects of palmitylcarnitine (3 X 10(-5) to 3 X 10(-4)M) with those of elevated external calcium is consistent with the hypothesis that palmitylcarnitine, like elevated external calcium, influences sodium and calcium channel operation by an effect on membrane surface charge.

Ultrastructural, functional, and metabolic correlates in the ischemic rat heart. Effects of free fatty acid

A study correlating functional, metabolic, and ultrastructural changes in the ischemic myocardium was conducted on isolated working rat hearts, both in the presence and absence of fatty acid. Glucose alone (11 mM) or glucose plus palmitic acid (1.5 mM) were used as metabolic substrates. A 60-min period of whole-heart ischemia resulted in a more dramatic morphological alteration in those hearts receiving palmitate than in those receiving no palmitate. In ischemic hearts receiving palmitate, intramitochondrial amorphous densities of both rounded and elongated types were observed. These densities did not develop in hearts receiving glucose alone over the same period of ischemia. Such morphological alterations were associated with a more severe deterioration of mechanical function in the presence of palmitate. Biochemical determinations of fatty acid derivatives showed increased tissue levels of acyl esters of CoA and carnitine in ischemic hearts, but levels of long-chain acyl carnitine were much higher in those ischemic hearts receiving palmitate. Furthermore, from the data obtained on isolated mitochondria, it appeared that the mitochondrial level of long-chain acyl carnitine was approximately four times higher in the ischemic hearts receiving palmitate than in those receiving no palmitate. This great rise in mitochondrial levels of long-chain acyl carnitine correlated with modifications of the mitochondrial structure and with the appearance of amorphous densities.

Effects of L-carnitine on tissue levels of free fatty acid, acyl CoA, and acylcarnitine in ischemic heart

In order to evaluate the protective effects of L-carnitine on ischemic myocardium, its effects on tissue levels of free fatty acid (FFA), acyl CoA, acyl carnitine, and adenosine triphosphate (ATP) were studied in ischemic dog hearts. Myocardial ischemia was induced by the ligation of left anterior descending coronary artery for 15 min. L-Carnitine (100 mg/kg) was administered intravenously prior to coronary ligation. In ischemic myocardium, tissue levels of free carnitine and ATP decreased, whereas long-chain acyl carnitine, long-chain acyl CoA, and FFA increased. Pretreatment of L-carnitine prevented the decrease in free carnitine and ATP and the increase in long-chain acyl carnitine and long-chain acyl CoA. A positive correlation was observed between ATP and free carnitine. On the other hand, a negative correlation was observed not only between ATP and the ratio of long-chain acyl CoA to free carnitine but also between ATP and the ratio of long-chain acyl carnitine to free carnitine. These results suggest that L-carnitine has protective effects on ischemic myocardium, probably by preventing the accumulation of long-chain acyl carnitine and long chain acyl CoA.

Partial purification of Na+-Ca2+ antiporter from plasma membrane of chick heart

To study Na+-Ca2+ exchange, proteins of membrane vesicles from chick hearts were solubilized with cholate in the presence of phospholipids and the cholate extract was treated with pronase. These purified proteoliposomes, reconstituted by subsequent dilution and centrifugation to eliminate the cholate, catalyzed Ca2+ uptake depending on the intraliposomal Na+ (Nai+) concentration. The maximal amount of Ca2+ accumulating in the liposomes was 140 nmol/mg protein and the initial rates of Nai+-dependent Ca2+ uptake were routinely 20 to 40 nmol/mg per 3 s at 25 degrees C, but only 2 to 4 nmol/mg per 3 s for the crude proteoliposomes from the cholate extract not treated with pronase. Thus the pronase treatment resulted in 10-fold purification. Nai+-dependent Ca2+ uptake by purified proteoliposomes was 30- to 50-fold higher than that by the initial membrane vesicles. The fundamental properties of Nai+-dependent Ca2+ uptake in purified proteoliposomes such as Km for Ca2+, the sensitivity for Na+ and pH dependency, were nearly equal to those in membrane vesicles and crude proteoliposomes. Thus, pronase treatment was very useful for obtaining reconstituted liposomes containing highly enriched Na+-Ca2+ antiporters which were functionally intact.

The alteration of rabbit skeletal sarcoplasmic reticulum function by N-acylethanolamine, a lipid associated with myocardial infarction

The ability of N-acylethanolamines (pharmacologically active lipid metabolites which accumulate in canine myocardium during experimentally induced infarctions) to alter Ca2+ fluxes in a biological membrane system was studied using sarcoplasmic reticulum vesicles prepared from rabbit skeletal muscle. The effects of two N-acylethanolamines, the N-oleyl and N-lauryl derivatives, were compared to those of the lipophilic drugs, dibucaine and propranolol. The rate and extent of Ca2+ sequestration, Ca2+-Mg2+-ATPase activity and retention time of Ca2+ by the vesicles were all stimulated at low concentrations of the four compounds studied and inhibited at higher concentrations. The stoichiometry between Ca2+-pumping rates and ATPase activity was partially "uncoupled" indicating that both the calcium pump and the membrane permeability were affected by the drugs. However, although all four compounds exhibited the same qualitative behavior, the effects of the two N-acylethanolamines were more pronounced than dibucaine and propranolol and occurred at much lower concentrations. These results suggest that the N-acylethanolamines may have important physiological effects in the myocardium and, at least at lower concentrations, stimulate myocardial contractility by increasing the rate of calcium flux across the sarcoplasmic reticulum.

Fatty acid effects on calcium influx and efflux in sarcoplasmic reticulum vesicles from rabbit skeletal muscle

Low concentrations of fatty acids inhibited initial Ca uptake by sarcoplasmic reticulum vesicles, the extent of inhibition varying with chain length and unsaturation in a series of C14-C20 fatty acids. Oleic acid was a more potent inhibitor of initial Ca uptake than stearic acid at 25 degrees C, whereas at 5 degrees C there was less difference between the inhibitory effects of low concentrations of these fatty acids. When the fatty acids were added later, during the phase of spontaneous Ca release that follow Ca uptake in reactions carried out at 25 degrees C 1-4 microM oleic and stearic acids caused Ca content to increase. This effect was due to marked inhibition of Ca efflux and slight stimulation of Ca influx. At concentrations of greater than 4 microM, both fatty acids inhibited the Ca influx that occurs during spontaneous Ca release; in the case of oleic acid, this inhibition resembled that of initial Ca uptake at 5 degrees C. The different effects of fatty acids at various times during Ca uptake reactions may be explained in part if alterations in the physical state of the membranes occur during the transition from the phase of initial Ca uptake to that of spontaneous Ca release.

Effects of palmitic acid and palmityl carnitine on calcium sequestration by rabbit skeletal sarcoplasmic reticulum vesicles

A number of long-chain fatty acids and fatty acid derivatives accumulate in the cytosol of ischemic myocardium. Although the functional significance of this accumulation in vivo remains unclear, these amphiphilic compounds may alter the functional properties of a variety of biological membranes in vitro. In this study, we investigated the effect of palmitic acid and palmityl carnitine on calcium sequestration by sarcoplasmic reticulum vesicles in the absence of calcium-precipitating anions. Palmitic acid, at micromolar concentrations, enhanced calcium sequestration in a concentration-dependent manner when present from the onset of the reaction or when added to calcium-filled vesicles. Under identical conditions, similar concentrations of palmityl carnitine inhibited calcium sequestration when present at the onset of the reaction and caused a rapid release of accumulated calcium when added to calcium-filled vesicles. Low concentrations of palmitic acid decreased the sensitivity of the sarcoplasmic reticulum to the inhibitory effects of palmityl carnitine. These results suggest that calcium pump function in the sarcoplasmic reticulum can be altered by the presence of amphiphilic compounds and that this alteration is dependent on both the structure and number of amphiphiles present.

Effect of substrates on the mechanical performance of rhesus monkey papillary muscle

This study examines the effect of different substrates on mechanical performance of excised papillary muscles from rhesus monkeys which had been divided into a control group and an experimental group fed a high fat diet for 5 months prior to sacrifice. The results show that performance is affected by availabel substrate for both groups. The performance of the experimental group was depressed relative to control with the short chain fatty acid, butyrate (C4), producing a monotonically decreasing force-frequency response. Relative to the other mammals, isolated rhesus papillary muscles exhibited a protracted treppe which was sensitive to beta-adrenergic blockade with propranolol.

Respiration-dependent calcium ion uptake by two preparations of cardiac mitochondria. Effects of palmitoyl-coenzyme A and palmitoylcarnitine on calcium ion cycling and nicotinamide nucleotide reduction state

Ca(2+) uptake and the effect of the uptake inhibitors palmitoyl-CoA and palmitoylcarnitine were examined in two preparations of dog cardiac mitochondria. Mitochondria prepared by using the Nagarse technique was 2.5-fold more active in respiration-dependent Ca(2+) uptake than were mitochondria isolated by using the Polytron procedure. Palmitoyl-CoA and palmitoylcarnitine inhibited Ca(2+) uptake in both preparations uncompetitively, with K(i,app) 0.4 and 20mum. Ca(2+)-uptake rates were related to, or influenced by, the concentration of mitochondrial reduced nicotinamide nucleotides, with uptake slowing as this concentration decreased. When most of the nicotinamide nucleotides was oxidized, Ca(2+) release and respiratory stimulation were observed. In the presence of Ruthenium Red and palmitoyl-CoA, oxidation of nicotinamide nucleotides was abolished and the time to Ca(2+) release was shortened corresponding to the time of onset of nicotinamide nucleotide oxidation in the absence of Ruthenium Red. The results suggest that NAD(P)H oxidation in the presence of rotenone was a consequence of Ca(2+) re-uptake and that net Ca(2+) release could be observed as reduced nicotinamide nucleotide concentrations declined. Although nicotinamide nucleotide oxidation occurred in the presence of rotenone, it was not linked in an apparent manner to acyl-group metabolism (palmitoylcarnitine was less effective than palmitoyl-CoA). Therefore either a by-pass of the rotenone block or a direct interaction of NAD(P)H with the Ca(2+)-uptake process was possible. Loss of NADH occurred before respiratory stimulation, and this loss may relate to decreased coupling efficiency at sites 2 and 3 of the respiratory chain, as suggested by others [Bhuvaneswaran & Wadkins (1978) Biochem. Biophys. Res. Commun.82, 648-654].