Effects of lysophosphatidylcholine on electrophysiological properties and excitation-contraction coupling in isolated guinea pig ventricular myocytes

Response mechanism of harmful algae Phaeocystis globosa to ocean warming and acidification

Simultaneous ocean warming and acidification will alter marine ecosystem structure and directly affect marine organisms. The alga Phaeocystis globosa commonly causes harmful algal blooms in coastal areas of eastern China. P. globosa often outcompetes other species due to its heterotypic life cycle, primarily including colonies and various types of solitary cells. However, little is known about the adaptive response of P. globosa to ocean warming and acidification. This study aimed to reveal the global molecular regulatory networks implicated in the response of P. globosa to simultaneous warming and acidification. After exposure to warming and acidification, the phosphatidylinositol (PI) and mitogen-activated protein kinase (MAPK) signaling pathways of P. globosa were activated to regulate other molecular pathways in the cell, while the light harvesting complex (LHC) genes were downregulated to decrease photosynthesis. Exposure to warming and acidification also altered the intracellular energy flow, with more energy allocated to the TCA cycle rather than to the biosynthesis of fatty acids and hemolytic substances. The upregulation of genes associated with glycosaminoglycan (GAG) degradation prevented the accumulation of polysaccharides, which led to a reduction in colony formation. Finally, the upregulation of the Mre11 and Rad50 genes in response to warming and acidification implied an increase in meiosis, which may be used by P. globosa to increase the number of solitary cells. The increase in genetic diversity through sexual reproduction may be a strategy of P. globosa that supports rapid response to complex environments. Thus, the life cycle of P. globosa underwent a transition from colonies to solitary cells in response to warming and acidification, suggesting that this species may be able to rapidly adapt to future climate changes through life cycle transitions.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

TRPC1/TRPC3 channels mediate lysophosphatidylcholine-induced apoptosis in cultured human coronary artery smooth muscles cells

The earlier study showed that lysophosphatidylcholine (lysoPC) induced apoptosis in human coronary artery smooth muscle cells (SMCs); however, the related molecular mechanisms are not fully understood. The present study investigated how lysoPC induces apoptosis in cultured human coronary artery SMCs using cell viability assay, flow cytometry, confocal microscopy, and molecular biological approaches. We found that lysoPC reduced cell viability in human coronary artery SMCs by eliciting a remarkable Ca2+ influx. The effect was antagonized by La3+, SKF-96365, or Pyr3 as well as by silencing TRPC1 or TRPC3. Co-immunoprecipitation revealed that TRPC1 and TRPC3 had protein-protein interaction. Silencing TRPC1 or TRPC3 countered the lysoPC-induced increase of Ca2+ influx and apoptosis, and the pro-apoptotic proteins Bax and cleaved caspase-3 and decrease of the anti-apoptotic protein Bcl-2 and the survival kinase pAkt. These results demonstrate the novel information that TRPC1/TRPC3 channels mediate lysoPC-induced Ca2+ influx and apoptosis via activating the pro-apoptotic proteins Bax and cleaved caspase-3 and inhibiting the anti-apoptotic protein Bcl-2 and the survival kinase pAkt in human coronary artery SMCs, which implies that TRPC1/TRC3 channels may be the therapeutic target of lysoPC-induced disorders such as atherosclerosis.

Differential effects of lysophosphatidylcholine and ACh on muscarinic K(+),non-selective cation and Ca(2+) currents in guinea-pig atrial cells

We compared the effects of lysophosphatidylcholine (LPC) and acetylcholine (ACh) on IK(ACh), ICa and a non-selective cation current (INSC) in guinea-pig atrial myocytes to clarify whether LPC and ACh activate similar Gi/o-coupled effector systems.　IK(ACh), ICa and INSC were analyzed in single atrial myocytes by the whole cell patch-clamp.　LPC induced INSC in a concentration-dependent manner in atrial cells.　ACh activated IK(ACh), but failed to evoke INSC.　LPC also activated IK(ACh) but with significantly less potency than ACh.　The effects of both ligands on IK(ACh) were inhibited by intracellular loading of pre-activated PTX.　This treatment also inhibited LPC-induced INSC, indicating that IK(ACh) and INSC induced by LPC are both mediated by Gi/o.　LPC and ACh had similar potencies in inhibiting ICa, which was pre-augmented by forskolin, indicating that LPC and ACh activate similar amounts of α-subunits of Gi/o.　The different effects of LPC and ACh on IK(ACh) and INSC may suggest that LPC and ACh activate Gi/o having different types of βγ subunits, and that LPC-induced INSC may be mediated by βγ subunits of Gi/o, which are less effective in inducing IK(ACh).

Deletion of the metabolic transcriptional coactivator PGC1β induces cardiac arrhythmia

AIMS

Peroxisome proliferator-activated receptor-γ coactivators PGC1α and PGC1β modulate mitochondrial biogenesis and energy homeostasis. The function of these transcriptional coactivators is impaired in obesity, insulin resistance, and type 2 diabetes. We searched for transcriptomic, lipidomic, and electrophysiological alterations in PGC1β(-/-) hearts potentially associated with increased arrhythmic risk in metabolic diseases.

METHODS AND RESULTS

Microarray analysis in mouse PGC1β(-/-) hearts confirmed down-regulation of genes related to oxidative phosphorylation and the electron transport chain and up-regulation of hypertrophy- and hypoxia-related genes. Lipidomic analysis showed increased levels of the pro-arrhythmic and pro-inflammatory lipid, lysophosphatidylcholine. PGC1β(-/-) mouse electrocardiograms showed irregular heartbeats and an increased incidence of polymorphic ventricular tachycardia following isoprenaline infusion. Langendorff-perfused PGC1β(-/-) hearts showed action potential alternans, early after-depolarizations, and ventricular tachycardia. PGC1β(-/-) ventricular myocytes showed oscillatory resting potentials, action potentials with early and delayed after-depolarizations, and burst firing during sustained current injection. They showed abnormal diastolic Ca(2+) transients, whose amplitude and frequency were increased by isoprenaline, and Ca(2+) currents with negatively shifted inactivation characteristics, with increased window currents despite unaltered levels of CACNA1C RNA transcripts. Inwardly and outward rectifying K(+) currents were all increased. Quantitiative RT-PCR demonstrated increased SCN5A, KCNA5, RYR2, and Ca(2+)-calmodulin dependent protein kinase II expression.

CONCLUSION

PGC1β(-/-) hearts showed a lysophospholipid-induced cardiac lipotoxicity and impaired bioenergetics accompanied by an ion channel remodelling and altered Ca(2+) homeostasis, converging to produce a ventricular arrhythmic phenotype particularly during adrenergic stress. This could contribute to the increased cardiac mortality associated with both metabolic and cardiac disease attributable to lysophospholipid accumulation.

Metabolism and atherogenic disease association of lysophosphatidylcholine

Lysophosphatidylcholine (LPC) is a major plasma lipid that has been recognized as an important cell signalling molecule produced under physiological conditions by the action of phospholipase A(2) on phosphatidylcholine. LPC transports glycerophospholipid components such as fatty acids, phosphatidylglycerol and choline between tissues. LPC is a ligand for specific G protein-coupled signalling receptors and activates several second messengers. LPC is also a major phospholipid component of oxidized low-density lipoproteins (Ox-LDL) and is implicated as a critical factor in the atherogenic activity of Ox-LDL. Hence, LPC plays an important role in atherosclerosis and acute and chronic inflammation. In this review we focus in some detail on LPC function, biochemical pathways, sources and signal-transduction system. Moreover, we outline the detection of LPC by mass spectrometry which is currently the best method for accurate and simultaneous analysis of each individual LPC species and reveal the pathophysiological implication of LPC which makes it an interesting target for biomarker and drug development regarding atherosclerosis and cardiovascular disorders.

Phospholipid Lysophosphatidylcholine as a Metabolic Trigger and HERG as an Ionic Pathway for Extracellular K+ Accumulation and “Short QT Syndrome” in Acute Myocardial Ischemia

The most profound abnormalities during acute myocardial ischemia are extracellular K(+) accumulation ([K(+)](o)- upward arrow) and shortening of action potential duration or QT interval (APD- downward arrow or QT- downward arrow), which are pivotal in the genesis of ischemic arrhythmias and sudden cardiac death. The ionic mechanisms however remained obscured. We performed studies in a rabbit model of acute global myocardial ischemia in order to explore ionic and metabolic mechanisms for ischemic [K(+)](o)- upward arrow and QT- downward arrow. Exogenous 1-palmitoyl-lysophosphatidylcholine (LPC-16) mimicked the low-perfusion ischemia to produce significant [K(+)](o)- upward arrow and QT- downward arrow. The [K(+)](o)- upward arrow and QT- downward arrow induced by either LPC-16 or ischemia were prevented by dofetilide, a blocker of rapid delayed rectifier K(+) current (I(Kr)), but not by blockers for other K(+) channels. Consistently, dofetilide efficiently abolished the ventricular tachy-arrhythmias induced by ischemia or LPC-16. LPC-16 remarkably shortened APD and enhanced the function of I(Kr) and HERG (the pore-forming subunit of I(Kr)). The effects of LPC-16 manifested with shorter APD (faster repolarization rate) and at more negative potential (membrane repolarization). Dofetilide abolished the I(Kr)/HERG enhancing and APD shortening effects of LPC-16. Our results suggest that LPC-16 accumulation/HERG enhancement may be a link between metabolic trigger and ionic pathway for ischemic [K(+)](o)- upward arrow and QTc- downward arrow. This represents the first documentation of I(Kr)/HERG as the ionic mechanism in ischemic [K(+)](o)- upward arrow and QTc- downward arrow. Inhibition of LPC-16 production and accumulation and/or of I(Kr)/HERG may be a promising therapeutic strategy to attenuate the incidence of lethal arrhythmias associated with ischemic heart disease.

Cut-off phenomenon in the protective effect of alcohols against lysophosphatidylcholine-induced calcium overload

We studied the effect of chain length on the protective effect of alcohols against lysophosphatidylcholine (LPC)-induced Ca2+ overload in neonatal rat cardiomyocytes. We previously found that ethanol retards Ca2+ elevation. Cells were loaded with the Ca2+-sensitive fluorophore fura-2, and changes in fluorescence were followed. The addition of 10 microM LPC increased Ca2+, which reached a plateau after an 8-10 min delay. The presence of 88 mM n-propanol, n-butanol, tert-butanol, or 2,2-dimethylpropanol significantly increased the delay by 94-213%. However, n-pentanol at 2 mM or 88 mM had no protective effect. Among n-alcohols, the increase in lag time was inversely proportional to the length of the carbon chain. Chain length, rather than molecular weight determines the effect, because 2,2-dimethylpropanol had a protective effect. The influence of alcohols on LPC micelle formation was estimated from the increase in octadecyl rhodamine B fluorescence; the increase by n-alcohols was directly proportional to chain length, indicating that micelle formation was not involved in the extension of lag time. The absence of the protective effect when the alcohol aliphatic chain exceeds four carbons suggests that the effect of ethanol may be mediated via a small lipophilic pocket on a protein, or to lateral pressure perturbation in the membrane.

Potential mechanisms for the enhancement of HERG K+ channel function by phospholipid metabolites

1. Phospholipid metabolites lysophospholipids cause extracellular K(+) accumulation and action potential shortening with increased risk of arrhythmias during myocardial ischemia. Here we studied effects of several lysophospholipids with different lengths of hydrocarbon chains and charged headgroups on HERG K(+) currents (I(HERG)) expressed in HEK293 cells and the potential mechanisms using whole-cell patch-clamp techniques. 2. Only the lipids with 16 hydrocarbons such as 1-palmitoyl-lysophosphatidylcholine (LPC-16) and 1-palmitoyl-lysophosphatidylglycerol (LPG-16) were found to produce significant enhancement of I(HERG) and negative shifts of HERG activation, although the voltage dependence of the effects was different between LPC-16 and LPG-16 which have differently charged headgroups. The lipid with 18 hydrocarbons modestly increased I(HERG). The lipids with 6 or 24 hydrocarbons had no effect or slightly decreased I(HERG). 3. Inhibition or activation of protein kinase C did not alter the effects of LPC-16 and LPG-16. Participation of phosphatidylinositol-4,5-bisphosphate in I(HERG) enhancement by LPC-16/LPG-16 was also excluded. 4. Vitamin E augmented the effects of LPC-16/LPG-16 whereas xanthine/xanthine oxidase reduced I(HERG): indicating that LPC-16/LPG-16 produced dual effects on I(HERG): direct enhancement of I(HERG) and indirect suppression via production of superoxide anion. 5. We conclude that enhancement of HERG function by lysophospholipids is specific to the lipids with 16-hydrocarbon chain structure and the pattern of voltage dependence is determined by the polar headgroups. The increase in I(HERG) is best described by direct interactions between lipid molecules and HERG proteins, which is consistent with lack of effects via membrane destabilization or modulation by intracellular signaling pathways.

Excitatory Neurotoxic Properties of Pontamine Sky Blue Make It a Useful Tool for Examining the Functions of Focal Brain Parts

Pontamine sky blue (PSB) is used in brain studies to mark the position of microelectrode and micropipette tips. However, few studies have been made on the effects of PSB on neurons; therefore we examined these effects. When puffed on isolated sensory ganglion cells of rats, PSB increased membrane conductance, depolarized membrane potential, and reduced the amplitude of action potentials. When dripped on frog sympathetic ganglion, much like hexamethonium, PSB decreased the amplitude of compound action potentials of the postganglionic strand. A bath application of PSB to sartorius muscle fibers that had been treated with tetrodotoxin depolarized the membrane potential and increased the frequency and amplitude of miniature end-plate potentials. All these effects were reversible. When injected into the rat's pontine part corresponding to the location of the canine pontine defecation reflex center, PSB produced repetitive colorectal contractions and irreversibly abolished them in response to anal-canal stimulation. The excitatory and blocking effects of PSB and its staining ability make it a useful tool for examining the functions of focal brain parts.

Anti-ischemic compound KC 12291 prevents diastolic contracture in isolated atria by blockade of voltage-gated sodium channels

Several lines of evidence support a fundamental role for voltage-gated sodium channels in mediating ischemic Na rise. We examined the effect of the novel anti-ischemic compound KC 12291 on veratridine-stimulated and lysophosphatidylcholine (LPC)-induced sustained sodium current (I(NAL)) mediated by sodium channels in isolated myocytes obtained from guinea-pig atria, by using the whole-cell patch-clamp technique. We also analyzed the effect of KC 12291 on veratridine- and LPC-induced contractures in isolated guinea-pig atria. Veratridine as well as LPC increased I(NAL) measured at 20 ms of a 2 s pulse evoked from -100 to -30 mV (47.5 and 12 pA/pF in the presence of 40 microM veratridine and 10 microM LPC, respectively, vs. 6.7 pA/pF under control conditions). A significant reduction by KC 12291 in the quantity of charge carried by veratridine-stimulated I(NAL) in the range of test potentials between -50 mV and +10 mV was observed and similar effects were obtained on LPC-induced I(NAL). Thus, the quantity of charge carried by LPC-induced I(NAL) over a 2 s pulse to -30 mV was reduced by 48% in the presence of 10 microM KC 12291 vs. a reduction by 50% of veratridine-stimulated I(NAL) at the same test potential. Veratridine- and LPC-induced submaximal contractures in isolated atria were significantly inhibited by KC 12291 in a concentration-dependent manner, with an IC of 0.55 microM and 0.79 microM, respectively. The data indicate that veratridine- and LPC-induced increases in diastolic tension are inhibited by KC 12291 by a mechanism that involves blockade of voltage-gated sodium channels mediating sustained sodium current.

Phospholipid metabolite 1-palmitoyl-lysophosphatidylcholine enhances human ether-a-go-go-related gene (HERG) K(+) channel function

BACKGROUND

Lysophosphatidylcholine (LPC), a naturally occurring phospholipid metabolite, accumulates in the ischemic heart and causes extracellular K(+) accumulation and action potential shortening. LPC has been incriminated as a biochemical trigger of lethal cardiac arrhythmias, but the underlying mechanisms remain poorly understood.

METHODS AND RESULTS

We studied the effect of 1-palmitoyl-LPC (Pal-LPC) on currents resulting from human ether-a-go-go-related gene (HERG) expression in human embryonic kidney (HEK) cells using whole-cell patch-clamp techniques. Bath application of Pal-LPC consistently and reversibly increased HERG current (I(HERG)). The effects of Pal-LPC were apparent as early as 3 minutes after application of the drug, reached maximum within 10 minutes, and were reversible on washout. Pal-LPC increased I(HERG) at voltages between -20 and +30 mV, with greater effects at stronger depolarization. However, Pal-LPC did not affect the voltage-dependence of I(HERG) activation. In contrast, Pal-LPC significantly shifted the inactivation curve toward more positive potentials, causing a mean 20.0+/-2.2 mV shift in half-inactivation voltage relative to control.

CONCLUSIONS

Our results indicate that apart from being a well-recognized target for drug inhibition, I(HERG) can also be enhanced by natural substances. An increase in I(HERG) by Pal-LPC may contribute to K(+) loss, abnormal electrophysiology, and arrhythmia occurrence in the ischemic heart.

Effects of arrhythmogenic lipid metabolites on the L-type calcium current of diabetic vs. non-diabetic rat hearts

Accumulation of lipid metabolites, such as palmitoylcarnitine and lysophosphatidylcholine, is thought to be a major contributor to the development of cardiac arrhythmias during myocardial ischemia. This arrhythmogenicity is likely due to the effects of these metabolites on various ion channels. Diabetic hearts have been shown to accumulate much higher concentrations of these lipid metabolites during ischemia, which may be an important factor in the enhanced incidence of arrhythmias in diabetic hearts. However, it is not known whether these metabolites have similar effects on the ion channels of diabetic hearts as in non-diabetic hearts. Previous studies on myocytes from non-diabetic hearts have reported either enhancement or inhibition of L-type calcium current (I(Ca)) by these lipid metabolites. Thus, it is not clear whether the effects of palmitoylcarnitine and/or lysophosphatidlycholine on I(Ca) contribute to the enhanced arrhythmogenicity of diabetic hearts or protect against arrhythmias. We determined the effect of exogenous palmitoylcarnitine and lysophosphatidylcholine on the (I(Ca)) in ventricular myocytes from streptozotocin-diabetic and non-diabetic rat hearts under identical conditions. We found that palmitoylcarnitine and lysophosphatidylcholine exhibited a dose-dependent inhibition of I(Ca), which was virtually identical in diabetic and non-diabetic cardiac myocytes. Thus, we conclude that these arrhythmogenic lipid metabolites have similar actions on calcium channels in diabetic and non-diabetic hearts. Therefore, the greater susceptibility of diabetic hearts to arrhythmias during myocardial ischemia is not due to an altered sensitivity of the L-type calcium channels to lipid metabolites, but may be explained, in large part, by the greater accumulation of these metabolites during ischemia.

Marked dissociation between intracellular Ca2+ level and contraction on exposure of rat aorta to lysophosphatidylcholine

We investigated the relationship between tension development and the cytosolic free Ca2+ level ([Ca2+]i) on exposure of the endothelium-denuded isolated rat aorta to palmitoyl-L-alpha-lysophosphatidylcholine. Lysophosphatidylcholine concentration-dependently induced a gradual increase in [Ca2+]i. Application of 10(-4) M lysophosphatidylcholine induced a large and sustained tonic increase in [Ca2+]i (the peak [Ca2+]i was 125.2 +/- 11.5% of the 80 mM K+-induced response) but only a small contraction (4.0 +/- 1.4% of the 80 mM K+ induced contraction). The sustained increase in [Ca2+]i was attenuated when extracellular Ca2+ was removed but it was unaffected by verapamil or 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride (H-7). Digitonin also produced a gradual increase in [Ca2+]i but with a pronounced contraction. Triton X-100 (0.1%) produced a marked elevation in [Ca2+]i with no detectable contraction. Triton X-100, however, caused a rapid leakage of fura PE-3. Treatment with 10(-4) M lysophosphatidylcholine for 1 or 2 h did not affect the contractile response induced by 80 mM K+ and this treatment did not release lactate dehydrogenase from the rat aorta. Treatment with lysophosphatidylcholine did not affect either the cyclic AMP level or the cyclic GMP level in endothelium-denuded aortic tissues. These results show that in the rat aorta lysophosphatidylcholine produces a large increase in [Ca2+]i (possibly in a non-contractile compartment) which does not induce contraction. Thus, the increase in [Ca2+]i induced by lysophosphatidylcholine (i) requires external Ca2+ but is not due to an increased Ca2+ influx through voltage-dependent L-type Ca2+ channels, (ii) is not primarily due to protein kinase C activation and (iii) is probably not due to a detergent action (like those of digitonin and triton X-100). The relative lack of a contractile response to lysophosphatidylcholine is not due to formation of cyclic AMP or cyclic GMP.

Cardiac ionic currents and acute ischemia: from channels to arrhythmias

The aim of this review is to provide basic information on the electrophysiological changes during acute ischemia and reperfusion from the level of ion channels up to the level of multicellular preparations. After an introduction, section II provides a general description of the ion channels and electrogenic transporters present in the heart, more specifically in the plasma membrane, in intracellular organelles of the sarcoplasmic reticulum and mitochondria, and in the gap junctions. The description is restricted to activation and permeation characterisitics, while modulation is incorporated in section III. This section (ischemic syndromes) describes the biochemical (lipids, radicals, hormones, neurotransmitters, metabolites) and ion concentration changes, the mechanisms involved, and the effect on channels and cells. Section IV (electrical changes and arrhythmias) is subdivided in two parts, with first a description of the electrical changes at the cellular and multicellular level, followed by an analysis of arrhythmias during ischemia and reperfusion. The last short section suggests possible developments in the study of ischemia-related phenomena.

Plasmalogen-derived lysolipid induces a depolarizing cation current in rabbit ventricular myocytes

Plasmalogen rather than diacyl phospholipids are the preferred substrate for the cardiac phospholipase A2 (PLA2) isoform activated during ischemia. The diacyl metabolite, lysophosphatidylcholine, is arrhythmogenic, but the effects of the plasmalogen metabolite, lysoplasmenylcholine (LPLC), are essentially unknown. We found that 2.5 and 5 micromol/L LPLC induced spontaneous contractions of intact isolated rabbit ventricular myocytes (median times, 27.4 and 16.4 minutes, respectively) significantly faster than lysophosphatidylcholine (>60 and 37.8 minutes, respectively). Whole-cell recordings revealed that LPLC depolarized the resting membrane potential from -83.5+/-0.2 to -21.5+/-1.0 mV. Depolarization was due to a guanidinium toxin-insensitive Na+ influx. The LPLC-induced current reversed at -18.5+/-0.9 mV and was shifted 26.7+/-4.2 mV negative by a 10-fold reduction of bath Na+ (Na+/K+ permeability ratio, approximately 0.12+/-0.06). In contrast, block of Ca2+ channels with Cd2+ and reducing bath Cl failed to affect the current. The actions of LPLC were opposed by lanthanides. Gd3+ and La3+ were equally effective inhibitors of the LPLC-induced current and equally delayed the onset of spontaneous contractions. However, the characteristics of lanthanide block imply that Gd3+-sensitive, poorly selective, stretch-activated channels were not involved. Instead, the data are consistent with the view that lanthanides increase phospholipid ordering and may thereby oppose membrane perturbations caused by LPLC. Plasmalogens constitute a significant fraction of cardiac sarcolemmal choline phospholipids. In light of their subclass-specific catabolism by phospholipase A2 and the present results, it is suggested that LPLC accumulation may contribute to ventricular dysrhythmias during ischemia.

Lysophosphatidylcholine and Cellular Potassium Loss in Isolated Rabbit Ventricle

BACKGROUND: Lysophospholipids such as lysophosphatidylcholine (LPC) have many direct electrophysiological effects on cardiac muscle and have been implicated as a cause of lethal ventricular arrhythmias during acute myocardial ischemia. Because extracellular K(+) accumulation is also a key arrhythmogenic factor during acute ischemia, we examined the effects of LPC on cellular K(+) balance, including its interaction with adenosine triphosphate-sensitive K(+) (K(ATP)) channels. METHODS AND RESULTS: Isolated rabbit interventricular septa paced at 75 beats/min were loaded with (42)K(+) to measure unidirectional K(+) efflux rate (in (42)K(+) washout experiments) or tissue K(+) content ((42)K(+) uptake experiments) and action potential duration (APD) during exposure to 20 µM LPC for 30 minutes. LPC caused tissue K(+) content to decrease by 15 +/- 2% (n = 4) at a steady rate over 30 minutes, associated with gradual APD shortening and a delayed increase in unidirectional K(+) efflux rate. Pretreatment with 12 µM cromakalim to selectively activate K(ATP) channels shortened APD by 44 +/- 66% and had no effect on net tissue K(+) content during control aerobic perfusion. However, cromakalim increased net K(+) loss during exposure to LPC to 22 +/- 4%, a 47% increase. CONCLUSIONS: LPC induced net K(+) loss in heart, which was potentiated by the K(ATP) channel agonist cromakalim. This ATP finding suggests that if LPC accumulates to similar levels during myocardial ischemia and hypoxia, it may be an important mechanism in net K(+) loss.

Modification of heart sarcolemmal phosphoinositide pathway by lysophosphatidylcholine

Although lysophosphatidylcholine (lyso-PtdCho) accumulates in the sarcolemmal (SL) membrane and alters its function during myocardial ischemia and diabetic cardiomyopathy, the effects of lyso-PtdCho on SL signalling processes have not yet been investigated. The present study was carried out to examine the actions of lyso-PtdCho on the rat heart SL membrane enzymes involved in the phosphoinositide pathway. Different lyso-PtdCho species (10 to 200 microM) inhibited the activities of both phosphatidylinositol kinase and phosphatidylinositol-4-phosphate kinase in the SL membrane in a concentration-dependent manner. The inhibitory potency of lyso-PtdCho compounds for phosphatidylinositol kinase was lyso-PtdCho plasmalogen > 1-oleoyl-lyso-PtdCho > 1-stearoyl-lyso-PtdCho > 1-palmitoyl-lyso-PtdCho, and that for phosphatidylinositol-4-phosphate kinase was lyso-PtdCho plasmalogen > 1-oleoyl-lyso-PtdCho > 1-palmitoyl-lyso-PtdCho > 1-stearoyl-lyso-PtdCho. The inhibitory effect of lyso-PtdCho on phosphatidylinositol-4-phosphate kinase was greater than that on phosphatidylinositol kinase. Lyso-PtdCho structural analogues, such as phosphatidylcholine, lysophosphatidic acid, lysophosphatidylethanolamine, L-alpha-glycerophosphate, oleate and phosphorylcholine, did not affect the phosphoinositide kinases, suggesting that the intact structure of lyso-PtdCho was required for the inhibition of the kinases. The detrimental action of lyso-PtdCho on PtdIns kinase was potentiated by acidosis. Unlike Ca2+, ATP (0.1 and 4 mM) increased lyso-PtdCho-induced deactivation of the kinases. Both enzyme activities were found to be depressed in the ischemic-reperfused or diabetic hearts. None of the tested lyso-PtdCho species altered phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) hydrolysis by SL phospholipase C. These results indicate that accumulation of lyso-PtdCho in the SL membrane under pathological conditions may diminish the availability of the PtdIns(4,5)P2 substrate for the production of second messengers by receptor-linked phospholipase C.

Differential effects of Ca2+ channel blockers on Ca2+ overload induced by lysophosphatidylcholine in cardiomyocytes

The effects of Ca2+ channel blockers (verapamil, diltiazem, nicardipine, bepridil and flunarizine) on Ca2+ overload induced by lysophosphatidylcholine were examined in rat isolated cardiomyocytes. Addition of lysophosphatidylcholine (15 microM) produced Ca2+ overload as evidenced by a marked increase in the concentration of intracellular Ca2+ and hypercontracture of cells. Verapamil, flunarizine and bepridil concentration dependently inhibited the lysophosphatidylcholine-induced Ca2+ overload, whereas diltiazem and nicardipine did not. Lysophosphatidylcholine increased the release of creatine kinase, which was significantly attenuated by verapamil, flunarizine or bepridil (5 microM for each), but not by diltiazem or nicardipine (20 microM for each). Verapamil, flunarizine, bepridil (which attenuated the lysophosphatidylcholine-induced Ca2+ overload) and nicardipine (which did not) inhibited the veratridine-induced increase in the concentration of intracellular Na+ (indicated by the increase in fluorescence ratio of Na(+)-binding benzofuran isophthalate) and cell contracture, whereas diltiazem did not. These results suggest that verapamil, bepridil and flunarizine attenuate the Ca2+ overload induced by lysophosphatidylcholine, and that the Ca2+ channel blocking action of these drugs does not contribute substantially to this effect. The Na+ channel inhibition together with high lipophilicity of these drugs may be important for the attenuation of the lysophosphatidylcholine-induced Ca2+ overload.

Extracellular divalent cations block a cation non-selective conductance unrelated to calcium channels in rat cardiac muscle

1. The effect of removing extracellular divalent cations on resting potential (Vrest) and background conductance of rat cardiac muscle was studied. Vrest was measured with 3 M KCl-filled microelectrodes in papillary muscles, or with a patch electrode in ventricular myocytes. Whole-cell membrane currents were measured in myocytes using step or ramp voltage commands. 2. In both muscles and single cells, decrease or removal of Ca2+o and Mg2+o caused a nifedipine-resistant depolarization, which was reversed upon readmission of Ca2+o or Mg2+o (half-maximal effect at 0.8 mM Ca2+o or 3 mM Mg2+o in muscles). 3. In single myocytes, removal of Ca2+o and Mg2+o had no effect on the seal resistance in nonruptured cell-attached recordings, but reversibly induced a current with a reversal potential (Vrev) of -8 +/- 3.4 mV (with internal Cs+; mean +/- S.E.M., n = 23) during whole-cell recordings. The current was insensitive to nifedipine (3-100 microM) or amiloride (1 mM). Vrev was insensitive to changes in the equilibrium potential for chloride ions (ECl). 4. The current induced in the absence of extracellular divalent cations was blocked in a concentration-dependent manner by Ca2+o. (At -80 mV, the affinity constant KCa was 60 microM with a Hill coefficient of 0.9) KCa was voltage dependent at positive but not negative potentials. Mg2+o, Ni2+o, Sr2+o, Ba2+o, Cd2+o and Gd3+o also blocked the current. 5. In 0 mM Na+ (145 mM NMDG+), the inward component of the divalent cation-sensitive current was decreased and Vrev shifted to more negative potentials. 6. These results suggest that a novel conductance pathway, permeable to monovalent cations but not to Cl- and blocked by divalent cations, exists in ventricular myocytes.

Na(+)-H+ exchange inhibition protects against mechanical, ultrastructural, and biochemical impairment induced by low concentrations of lysophosphatidylcholine in isolated rat hearts

Lysophophatidylcholine (LysoPC) accumulates rapidly in the ischemic myocardium and is an important mediator of ischemia-induced cell injury. Na(+)-H+ exchange (NHE) inhibition has been demonstrated to protect the ischemic and reperfused myocardium. We determined whether NHE inhibition can also modulate cardiotoxicity produced by LysoPC (3 and 5 mumol/L) in isolated rat hearts. At 3 mumol/L, LysoPC produced a depression in left ventricular developed pressure (LVDP) and elevation in left ventricular end-diastolic pressure (LVEDP), which were 19 +/- 7% and 1290 +/- 205% of pre-LysoPC values, respectively, after 30 minutes of treatment. In the presence of the NHE inhibitor 4-isopropyl-3-methylsulfonylbenzoyl-guanidine methanesulfonate (HOE 642, 5 mumol/L), LVDP was reduced to only 80.8 +/- 8.6%, and LVEDP increased to 270 +/- 32% (P < .05 for both parameters). LysoPC significantly depressed tissue ATP, creatine phosphate, and glycogen contents and increased lactate levels, all of which were significantly attenuated by HOE 642. Moreover, marked LysoPC-induced ultrastructural abnormalities, including mitochondrial and myofibrillar disruption, were totally prevented by HOE 642. This protection was mimicked by another NHE inhibitor, methylisobutylamiloride (5 mumol/L). HOE 642 was also effective against injury produced by 5 mumol/L LysoPC although, generally, the protection was less marked than that observed against 3 mumol/L; LVDP depression after 30 minutes was 10.1 +/- 4.3% and 41.4 +/- 10.4% of pre-LysoPC values in control and HOE 642-treated hearts, respectively (P < .05), whereas corresponding LVEDP elevations were 1629 +/- 393% and 990 +/- 144% (P > .05). In myocytes superfused with bicarbonate-free buffer subjected to acid loading by NH4Cl pulsing, pH recovery (as measured by acid flux) was significantly stimulated by 3 mumol/L LysoPC, indicative of NHE activation. Our study shows that cardiac injury produced by low concentrations of LysoPC can be effectively attenuated by NHE inhibition. The results also suggest that the beneficial effects of NHE inhibitors on the ischemic myocardium may be, at least partially, mediated by inhibiting the deleterious effects of LysoPC.

Study of the acrosome reaction and the fertilizing ability of hamster epididymal cauda spermatozoa treated with antibodies against phospholipase A2 and/or lysophosphatidylcholine

The present report describes experiments in vitro that were designed to evaluate the involvement of phospholipase A2 (PLA2) in the acrosome reaction of mammalian sperm and the interaction of gametes. Hamster spermatozoa were incubated in a defined medium (TALP) to induce capacitation and the acrosome reaction. This medium was supplemented with antibodies against porcine pancreatic PLA2 and/or lysophosphatidylcholine (LPC). For in vitro fertilization, spermatozoa and/or oocytes were incubated in TALP medium that contained PLA2-specific antibodies, LPC, or antibodies plus LPC. The antibodies inhibited the acrosome reaction in a dose-dependent manner, without any effect on sperm motility or hyperactivation. These antibodies also inhibited fertilization in vitro. LPC, a product of the reaction catalysed by PLA2, speeds up and synchronizes the acrosome reaction and facilitates penetration of the zona pellucida by spermatozoa, the fusion process and polyspermy. The results of addition of the antibodies plus LPC showed that LPC is able to reverse the inhibitory effects of the antibodies on the acrosome reaction and fertilization. It is possible that endogenous PLA2 plays a role in the final stages of the acrosome reaction and the interaction of gametes, perhaps through one of its reaction products, LPC. The role of LPC might be to stimulate the fertilizing ability of spermatozoa, as well as to induce changes in the zona pellucida and the oolemma that allow sperm-egg fusion. Thus, it seems possible that PLA2 and one of its reaction products might contribute to membrane-fusion events during mammalian fertilization.

Effects of beta-adrenoceptor antagonists on Ca(2+)-overload induced by lysophosphatidylcholine in rat isolated cardiomyocytes

1. The effects of beta-adrenoceptor antagonists including (-)- and (+)-propranolol, (-)- and (+)-penbutolol, timolol, pindolol, atenolol, acebutolol and practolol on the Ca(2+)-overload induced by lysophosphatidylcholine (LPC) were examined in isolated cardiomyocytes of the rat. 2. Fura-2 was used for measurement of the intracellular calcium concentration ([Ca2+]i). LPC (15 microM) produced a rapid increase in [Ca2+]i from 72 +/- 5 to 3042 +/- 431 nM which coincided with a decrease in the percentage of rod-shaped cells from 69 +/- 2 to 5 +/- 2%. 3. Preincubation with (-)-propranolol (20 microM), (+)-propranolol (50 microM), or (-)- or (+)-penbutolol (20 microM), the lipophilicity of which is higher than other beta-adrenoceptor antagonists, significantly inhibited both the increase in [Ca2+]i and the cell-shape change induced by 15 microM LPC. The inhibitory effects of the four drugs on the LPC-induced increase in [Ca2+]i and cell-shape change were concentration-dependent. The IC50S of (-)-propranolol, (+)-propranolol, (-)- and (+)-penbutolol for the increase in [Ca2+]i were 1.28, 10.50, 0.67 and 0.76 microM, respectively. 4. Pretreatment with pindolol, timolol, acebutolol, practolol, atenolol or lignocaine did not inhibit the increase in [Ca2+]i and the morphological change induced by LPC. 5. LPC markedly increased the release of creatine phosphokinase from 9 +/- 1 to 45 +/- 2% which could be significantly reduced by (-)- or (+)-propranolol but not by acebutolol or timolol. 6. The protective effects of (-)- and (+)-propranolol, (-)- and (+)-penbutolol against the Ca(2+)-overload induced by LPC were not associated with the beta-adrenoceptor antagonistic action, but probably with an unknown action which is related to the preservation of membrane integrity. Further studies are necessary to clarify the exact mechanisms of the protective action of these beta-adrenoceptor antagonists against the Ca(2+)-overload induced by LPC.

Exogenous lysophosphatidylcholine increases non-selective cation current in guinea-pig ventricular myocytes

Whole cell, patch-clamp studies were performed to examine the effect of lysophosphatidylcholine (LPC) on the membrane current in guinea-pig ventricular myocytes. The addition of 10 microM LPC to the external solution induced a membrane current which had a reversal potential of 0 mV. When Na+, the main cation in the external solution, was replaced by either K+, N-methyl-D-glucamine (NMG) or 90 mM Ca2+, LPC induced a current with the reversal potential near 0 mV, indicating that the current passed through a Ca2+-permeable non-selective cation channel. The order of the cationic permeability calculated from the reversal potential of the current was Cs+ > K+ > NMG > Na+ > Ca2+. Cl- did not pass through the LPC-induced channel. The LPC-induced current was not blocked by Gd3+ in the external solution, nor by the absence of Ca2+ in the pipette solution. In conclusion, LPC induces a Ca2+-permeable non-selective cation channel in guinea-pig ventricular myocytes.

Antigen-induced generation of lyso-phospholipids in human airways

The goal of the current study was to examine the formation of phospholipids, 1-radyl-2-lysosn-glycero-phospholipids (lyso-PL) and 2-acetylated phospholipids (such as PAF) as well as mechanisms responsible for generating these phospholipids in bronchoalveolar lavage fluid (BAI.F) from allergic subjects challenged with antigen. Bronchoalveolar lavage was performed in normal and allergic subjects before, 5-30 min, 6 h, and 20 h after segmental antigen challenge via a wedged bronchoscope. Levels of 1-hexadecyl-2-lyso-phospholipids and 1-hexadecyl-2-acetyl-phospholipids were initially determined by negative ion chemical ionization gas chromatography/mass spectrometry (NICI-GC/MS). Antigen dramatically elevated quantities of 1-hexadecyl-2-lyso-phospholipids in allergic subjects 20 h after challenge when compared to non-allergic controls. In contrast, there was not a significant increase in levels of 1-hexadecyl-2-acetyl-phospholipids after antigen challenge. Closer examination of 1-radyl-2-lyso-sn-glycero-3-phosphocholine (GPC) revealed that 1-palmitoyl-2-lyso-GPC, 1-myristoyl-2-lyso-GPC and 1-hexadecyl-2-lyso-GPC were three major molecular species produced after antigen challenge. 1-palmitoyl-2-lyso-GPC increased sevenfold to levels of 222 +/- 75 ng/ml of BALF 20 h after antigen challenge. The elevated levels of lyso-PL correlated with levels of albumin used to assess plasma exudation induced by allergen challenge. In contrast, the time course of prostaglandin D2 (PGD2) or 9 alpha, 11 beta PGF2 (11 beta PGF2) formation did not correlate with lyso-PL generation. To examine the mechanism leading to lyso-phospholipid formation in antigen-challenged allergic subjects, secretory phospholipase A2 (PI.A2) and acetyl hydrolase activities were measured. There was a significant increase in PLA2 activity found in BALF of allergic subjects challenged with antigen when compared to saline controls. This activity was neutralized by an antibody directed against low molecular mass, (14 kD) human synovial PLA2 and dithiothreitol. Acetyl hydrolase activity also markedly increased in BALF obtained after antigen challenge. This study indicates that high levels of lyso-PLs are present in airways of allergic subjects challenged with antigen and provides evidence for two distinct mechanisms that could induce lyso-PL formation. Future studies will be necessary to determine the ramifications of these high levels of lyso-phospholipids on airway function.

Protective effects of free polyunsaturated fatty acids on arrhythmias induced by lysophosphatidylcholine or palmitoylcarnitine in neonatal rat cardiac myocytes

Cultured, spontaneously beating, neonatal rat cardiac myocytes were used to examine the effects of various free fatty acids added to the medium perfusing the cells on lysophosphatidylcholine (LPC)- or acylcarnitine-induced arrhythmias. Perfusion of the cells with LPC or palmitoylcarnitine (2-10 microM) induced sustained tachyrhythmia with episodes of spasmodic contractures and fibrillation. Free PUFA (10-15 microM) including eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), alpha-linolenic acid (18:3n-3), arachidonic acid (AA, 20:4n-6) and linoleic acid (18:2n-6) were able to effectively prevent as well as terminate the LPC or acylcarnitine-induced arrhythmias. In contrast, monounsaturated oleic acid (18:1n-9) and saturated stearic acid (18:0) did not have such effects. The protective effects of the polyunsaturated fatty acids (PUFA) could be reversed by cell perfusion with delipidated bovine serum albumin. To determine the potential primary action by which the PUFA exert the antiarrhythmic effects, measurements of intracellular Ca2+ levels and the response of the cells to electrical pacing in the absence or presence of the PUFA were performed and the effects of verapamil (a L-type Ca2+ channel blocker), tetrodotoxin (a Na+ channel blocker) and Ca2+ ionophore A23187 on the cell contraction and the cytosolic Ca2+ levels were compared with that of the PUFA. Results suggest that an inhibitory effect on the electrical automaticity/excitability of the cardiac myocyte rather than a reduction in cytosolic Ca2+ underlie the protective effects of PUFA. In conclusion, free PUFAs are able to effectively protect the cardiac myocytes against the arrhythmias induced by low concentrations of lysophosphatidylcholine or palmitoylcarnitine.

Lysophosphatidylcholine causes Ca2+ influx, enhanced DNA synthesis and cytotoxicity in cultured vascular smooth muscle cells

The effects of lysophosphatidylcholine (LPC), a vasoactive phospholipid, on intracellular free calcium concentration ([Ca2+]i), DNA synthesis and cytotoxicity of vascular smooth muscle cells (VSMC) were studied. LPC from 10(-7) to 10(-5) mol/l dose-dependently induced a sustained increase in [Ca2+]i. In contrast to the response of [Ca2+]i induced by angiotensin II, that induced by LPC was totally abolished when extracellular Ca2+ was removed, was not affected by pretreatment of the cells with islet-activating protein, and was not desensitized by repeated addition. 8-(N,N-Diethylamino)octyl 3,4,5-trimethoxybenzoic acid (TMB-8), an inhibitor of Ca2+ release from intracellular Ca2+ stores, 1-(5-isoquinolinesulfonyl)-2-methylpiperadine dihydrochloride (H-7), an inhibitor of protein kinase C, KT5823, an inhibitor of protein kinase G, and Ca2+ channel blockers failed to suppress the LPC-induced increase in [Ca2+]i. LPC at 10(-5) mol/l caused significant stimulation of [3H]thymidine incorporation into VSMC, and at concentrations of 10(-5) mol/l and higher dose-dependently stimulated release of lactate dehydrogenase in cell culture supernatants. Moreover, digitonin mimicked the effects of LPC on [Ca2+]i, and also caused similar effects to those of LPC on DNA synthesis and cytotoxicity in VSMC. These observations suggest that LPC causes both cell growth and cell injury of VSMC, at least partly, through its detergent action, causing membrane leakiness and resultant [Ca2+]i overload in vitro, thus indicating the possible participation of LPC in atherosclerosis and/or injury of the vascular wall.

Excitation-contraction coupling in single guinea-pig ventricular myocytes exposed to hydrogen peroxide

1. The effects of hydrogen peroxide (H2O2), an in vitro free radical generating system, on excitation-contraction (E-C) coupling were studied in isolated adult guinea-pig ventricular myocytes using Ca(2+)-sensitive dyes and the patch-clamp technique. 2. In paced myocytes loaded with indo-1 AM, 1 mM H2O2 briefly increased, then decreased the amplitude of intracellular Ca2+ ([Ca2+]i) transients and cell contractions. Diastolic [Ca2+]i increased in association with cell shortening. Automaticity also developed, followed shortly by inexcitability. In contrast, paced myocytes exposed to the metabolic inhibitors carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) and 2-deoxyglucose (DG), rapidly became inexcitable and exhibited marked diastolic shortening prior to increases in diastolic [Ca2+]i. 3. In patch-clamped myocytes loaded with fura-2, H2O2 reduced the amplitude of the Ca2+ current (ICa), the [Ca2+]i transient, and active cell shortening. H2O2 prolonged the relaxation phase of the [Ca2+]i transient, and activated an outward membrane current consistent with the ATP-sensitive K+ current (IK,ATP), but did not change the voltage dependence of ICa, the peak [Ca2+]i transient or active cell shortening. These responses were qualitatively similar to patch-clamped myocytes exposed to FCCP and DG. 4. Following exposure to H2O2, ICa elicited smaller [Ca2+]i transients than under control conditions. This was consistent with the observation that H2O2 reduced sarcoplasmic reticulum (SR) stores of Ca2+ by 42%, when assessed by observing the [Ca2+]i transients elicited by rapid extracellular application of 5 mM caffeine. In contrast FCCP-DG tended to increase SR Ca2+ stores. 5. Despite the decrease in the caffeine-induced Ca2+i release after H2O2, there was an increase in the Na(+)-Ca2+ exchange current associated with the caffeine-induced [Ca2+]i transient. 6. We conclude, therefore, that as with metabolic inhibitors, H2O2 interferes with E-C coupling in guinea-pig myocytes by impairing ICa and activating IK,ATP. However, unlike metabolic inhibitors, H2O2 stimulates Na(+)-Ca2+ exchange and depletes SR Ca2+ stores. Furthermore, diastolic [Ca2+]i becomes elevated while the myocyte is still excitable. These observations suggest that free radicals have primary effects on cardiac E-C coupling independent of their depressant effects on metabolism.

Lactate transport in mammalian ventricle. General properties and relation to K+ fluxes

Net cellular L-lactate efflux associated with accelerated anaerobic glycolysis has been implicated as a potential cause of the marked cellular K+ loss contributing to lethal cardiac arrhythmias in ischemic heart and to impaired function of fatigued skeletal muscle. To examine the mechanisms of transsarcolemmal L-lactate movement in the heart, isolated guinea pig ventricular myocytes were loaded with the fluorescent H+ or K+ indicators, carboxy SNARF-1 or PBFI, respectively, under whole-cell patch-clamp conditions. With H+ as the only permeable monovalent cation, a rapid increase in extracellular L-lactate concentration ([L-]o) from 0 to 30 mmol/L at constant pHo (7.35) caused an intracellular acidification averaging 0.18 +/- 0.02 pH units in 60 seconds (n = 7), reflecting L-lactate influx in association with H+ influx (or OH- efflux). Under voltage-clamp conditions, no significant electrogenic current was associated with H(+)-coupled L-lactate influx, and membrane potential (-75 to +75 mV) had no effect on the degree of acidification produced by 30 mmol/L [L-]o, indicating that L-lactate influx was predominantly nonelectrogenic. Acidification in response to increased [L-]o was saturable (Km, approximately 5 mmol/L), partially stereospecific for L-lactate over D-lactate, and inhibited by 55 +/- 7% and 82 +/- 7% by the monocarboxylate carrier inhibitors alpha-cyano-4-hydroxycinnamate and mersalyl acid, respectively, consistent with a carrier-mediated transport mechanism. Extracellular K+ inhibited H(+)-coupled L-lactate influx by 36 +/- 2%, suggesting that K+ either inhibited or substituted for H+ in cotransport with L-lactate. However, in myocytes loaded with PBFI, no significant increase in [K+]i was detected during exposure to 30 mmol/L [L-]o, suggesting that only a minor component, if any, of L-lactate influx was cotransported or codiffused with K+.

Properties of cardiac I(leak) induced by photosensitizer-generated reactive oxygen

We reported previously that photomodification of single frog cardiac cells by Rose Bengal induces a time-independent current, designated I(leak)++, having a linear current-voltage (I/V) relationship. The purpose of the present study is to better characterize the properties of I(leak)++. Initially, I(leak)++ has a reversal potential (ER) near -70 mV, but with time, ER shifts toward a final value near 0 mV. This shift in ER is accompanied by a marked increase in conductance (slope of I/V relationship). Evidence is presented that the depolarizing shift in ER with time during photomodification results from a loss of membrane selectivity allowing sodium to make an increasing contribution to I(leak)++. Potassium also contributes to I(leak)++, as indicated by marked depolarizing shifts in ER following replacement of intracellular potassium with either cesium or tetraethylammonium. Since these results occur in calcium-free external media, the depolarizing shifts in ER and increased conductance are not related to activation of a calcium-dependent nonselective cation channel. However, I(leak) does have some properties similar to nonselective cation currents recently reported to be activated by membrane breakdown products such as arachidonic acid and lysophosphoglycerides.

Lysophosphatidylcholine disrupts the acrosome of tammar wallaby (Macropus eugenii) spermatozoa

The acrosomal status of wallaby spermatozoa was evaluated by light and electron microscopy after incubation in 1-100 microM lysophosphatidylcholine (LPC) for up to 120 min. Treatment with 1 and 10 microM LPC for 120 min did not lead to acrosomal loss, or detectable alteration to the acrosome, as detected by Bryan's staining and light microscopy. Incubation with 25 microM LPC had little effect on acrosomal loss, however statistically significant changes (P < 0.05) in the acrosomal matrix (altered) were detected after 10-min incubation by light microscopy. Around 50% of acrosomes were altered after 20-min incubation in 50 microM LPC (P < 0.001), and 40% of spermatozoa had lost their acrosome after 60-min incubation (P < 0.001). Treatment with 75 and 100 microM LPC led to rapid acrosomal loss from around 50% of spermatozoa within 10 min (P < 0.001), and by 60 min acrosomal loss was 70-80%. LPC, like the diacylglycerol DiC8 (1,2-dioctanoyl-sn-glycerol), is thus an effective agent to induce loss of the relatively stable wallaby sperm acrosome, and it also induces changes within the acrosomal matrix. Ultrastructure of the LPC-treated spermatozoa revealed that the plasma membrane and the acrosomal membranes were disrupted in a manner similar to that seen after detergent treatment (Triton X-100). There was no evidence of point fusion between the plasma membrane overlying the acrosome and the outer acrosomal membrane. The plasma membrane was the first structure to disappear from the spermatozoa. The acrosomal membranes and matrix showed increasing disruption with time and LPC concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Inward sodium current at resting potentials in single cardiac myocytes induced by the ischemic metabolite lysophosphatidylcholine

To investigate possible ionic current mechanisms underlying ischemic arrhythmias, we studied single Na+ channel currents in rat and rabbit cardiac myocytes treated with the ischemic metabolite lysophosphatidylcholine (LPC) using the cell-attached and excised inside-out patch-clamp technique at 22 degrees C. LPC has been reported previously to reduce open probability and to induce sustained open channel activity at depolarized potentials. We now report two new observations for Na+ currents in LPC-treated patches: 1) The activation-voltage relation of the peak of the ensemble currents is shifted in the negative (hyperpolarizing) direction by approximately 20 mV compared with control currents. This effect was observed in all patches for depolarizations from a holding potential of -150 mV to different test potentials. 2) In some LPC-treated patches, Na+ channels exhibited sustained bursting activity at potentials as negative as -150 mV, giving a nondecaying inward current. This bursting activity was accompanied by double and triple simultaneous openings and closings, suggesting tight cooperativity in channel gating. These LPC-modified channels were identified as Na+ channels, because their unitary conductance was the same as Na+ channels in control solutions, because the single channel current-voltage relation was extrapolated to reverse at the Na+ Nernst potential, and because the current was blocked by the local anesthetic QX-222. This novel depolarizing current may play a role in the electrophysiological abnormalities in ischemia, including abnormal automaticity and reentrant arrhythmias, and could be a target for antiarrhythmic drugs.