Biomedical subjects

J A Post

Publications and source records attributed to J A Post.

At least 55 records · Page 3Linked to original sources

PubMed1992

Removal of sarcolemmal sialic acid residues results in a loss of sarcolemmal functioning and integrity.

Treatment of neonatal rat heart cells with neuraminidase results in a large increase of cellular-associated Ca2+. The study described below was designed to test the hypothesis that neuraminidase produces its effects by increasing the transient Ca2+ channel current, as proposed by Yee et al. (24). This ICa,T can be inactivated by dodecylsulfate (DDS) (17). The experimental data show that 1) the increase in cellular Ca2+ during neuraminidase treatment cannot be explained by an increased ICa,T; 2) neuraminidase treatment has a much more profound effect on sarcolemmal permeability than has been recognized previously; and 3) the effect of neuraminidase treatment can be prevented by 50 microM DDS. The study indicates that glycocalyx-lipid bilayer interactions are important in maintenance of selective permeability of the sarcolemma. The protective effect of 50 microM DDS is probably mediated by insertion of the negatively charged amphiphilic molecule in the sarcolemma, although the exact mechanism remains to be elucidated.

Animals↗

PubMed1991

The isolated neonatal rat-cardiomyocyte used in an in vitro model for 'ischemia'. I. A morphological study.

Cultured heart cells have been recently shown to be useful for analysing states of oxygen- and volume-restrictions, conditions that are known to simulate anoxia and ischemia at the cellular level. In the present study, we examined the ultrastructural damage caused to cultured neonatal rat heart cells when they were subjected to simulated ischemia by volume restricted anoxia ('ischemia') in an in vitro system. Both thin-sectioning and freeze-fracturing electron microscopy revealed a mitochondrial reorganization after 30 min of 'ischemia', whereas multilamellar structures could be detected inside the mitochondria after another 30 min. At this time-point, changes were also observed regarding the organization of the sarcolemma. In addition to a slight aggregation of the intramembranous particles (IMP's) we found an extensive extrusion of particle-free multilamellar membrane-structures, possibly due to a loss of the sarcolemma/cytoskeleton-interaction. These morphological changes are comparable to those previously observed in in vivo and Langendorff studies and the results of the present study therefore underline the usefulness of this recently introduced model for ischemia.

Animals↗

PubMed1991

Effects of charged amphiphiles on cardiac cell contractility are mediated via effects on Ca2+ current.

Exposure of isolated adult rabbit myocytes to the negatively charged amphiphile dodecylsulfate (DDS; 10 microM) increased the contraction amplitude to 185% of control. The positively charged amphiphile dodecyltrimethylammonium (DDTMA; 10 microM) decreased the amplitude to 58%. DDS increased Ca2+ uptake by the same cells, but this uptake was partially prevented by nifedipine. DDTMA had no effect on Ca2+ uptake. Ca2+ binding to isolated sarcolemma of neonatal heart cells was increased by 10 microM DDS and, at higher concentrations, reduced by DDTMA. Single-cell voltage-clamp studies, using isolated rabbit myocytes, showed that DDS enhanced L-type Ca2+ currents (ICa,L), whereas DDTMA depressed ICa,L. DDS shifted current-voltage (I-V) and isochronal inactivation curves of ICa,L in the negative direction, whereas DDTMA shifted them in positive direction. Furthermore, DDS depressed T-type Ca2+ currents (ICa,T), and DDTMA enhanced ICa,T. The inotropic effects of the amphiphiles are therefore mediated to a significant degree by ICa,L. The shifts in the I-V and inactivation curves of ICa,L and the effect on ICa,T can be explained by changes in the actual membrane potential (Em), induced by the insertion of the amphiphiles in the outer monolayer of the sarcolemma. However, the changes in the Em do not explain the effect on the maximal current, indicating effects on the channel per se, possibly by an alteration of the lipid environment.

Action Potentials↗

PubMed1990

Is acidosis the clue to the loss of structure and functioning of the sarcolemma?

The only way for a tissue or organ to survive ischemia is by reperfusion or restoration of the blood flow. However, if the ischemic period is too long reperfusion leads to a Ca2+ overload of the myocardial cells and thereby to cell death. The question is; what are the key events during ischemia which cause this transition from reversible to irreversible injury. In this article we discuss whether acidosis may play a crucial role by inducing Ca2+ release from the sarcolemma and reorganization of membrane components especially the membrane lipids, i.e. lateral phase separation, resulting in membrane protein clustering and changes in lipid asymmetry.

Acidosis↗

PubMed1990

Composition and organization of sarcolemmal fatty acids in cultured neonatal rat cardiomyocytes.

This paper describes studies on the fatty acid composition of individual phospholipids of the neonatal rat cardiomyocyte as well as in the gas-dissected sarcolemma derived from those cells. There is a sarcolemmal fatty acid asymmetry between the two leaflets of the membrane, which results from an asymmetric phospholipid distribution and particular fatty acid composition of each phospholipid class. The cytoplasmic leaflet is shown to be more unsaturated than the outer one. The phospholipids preferring the inner sarcolemmal leaflet (PE, PS, and PI) are particularly rich in two fatty acids, stearic acid and arachidonic acid. The implications of the data in current models for Ca2+ binding and for disruption of sarcolemma following ischemia and reperfusion damage are discussed.

Animals↗

PubMed1988

Plasmalogen content and distribution in the sarcolemma of cultured neonatal rat myocytes.

Phospholipids are believed to play an important role in pathology and physiology of the myocardium. Because of the distinct physico-chemical properties of plasmalogens we studied the plasmalogen content and distribution in the sarcolemma of cultured rat myocytes. Treatment with phospholipase A2 degraded all glycerophospholipids in the outer monolayer. The hydrolysis products were analyzed for plasmalogen content. It is shown that the inner sarcolemmal leaflet is highly enriched in phosphatidylcholine and ethanolamine plasmalogen. This distribution of the plasmalogens might affect bilayer stability and thereby be involved in the destruction of the sarcolemma upon ischemia and reperfusion.

Animals↗

PubMed1988

Phospholipid asymmetry in cardiac sarcolemma. Analysis of intact cells and 'gas-dissected' membranes.

The investigation focuses on the phospholipid composition of the sarcolemma of cultured neonatal rat heart cells and on the distribution of the phospholipid classes between the two monolayers of the sarcolemma. The plasma membranes are isolated by 'gas-dissection' technique and 38% of total cellular phospholipid is present in the sarcolemma with the composition: phosphatidylethanolamine (PE) 24.9%, phosphatidylcholine (PC) 52.0%, phosphatidylserine/phosphatidylinositol (PS/PI) 7.2%, sphingomyelin 13.5%. The cholesterol/phospholipid ratio of the sarcolemma is 0.5. The distribution of the phospholipids between inner and outer monolayer is defined with the use of two phospholipases A2, sphingomyelinase C or trinitrobenzene sulfonic acid as lipid membrane probes in whole cells. The probes have access to the entire sarcolemmal surface and do not produce detectable cell lysis. The phospholipid classes are asymmetrically distributed: (1) the negatively charged phospholipids, PS/PI are located exclusively in the inner or cytoplasmic leaflet; (2) 75% of PE is in the inner leaflet; (3) 93% of sphingomyelin is in the outer leaflet; (4) 43% of PC is in the outer leaflet. The predominance of PS/PI and PE at the cytoplasmic sarcolemmal surface is discussed with respect to phospholipid-ionic binding relations between phospholipids and exchange and transport of ions, and the response of the cardiac cell on ischemia-reperfusion.

Animals↗

PubMed1988

Phospholipid reorganization and bilayer destabilization during myocardial ischemia and reperfusion: a hypothesis.

The ultrastructure of myocardial tissue was studied during ischemia and reperfusion and during reperfusion with a calcium-containing solution after a short period of calcium-free perfusion (calcium paradox). After ischemia an aggregation of the sarcolemmal intramembranous particles was observed. Subsequent reperfusion resulted in further aggregation of the intramembranous particles and disruption of the sarcolemma, which was attended with the formation and extrusion of multilamellar, lipidic structures. Similar ultrastructural changes of the sarcolemma were observed during the calcium paradox. Our hypothesis is that these changes are a result of lateral phase separation of the membrane phospholipids and destabilization of the lipid bilayer. This reorganization of phospholipids may be induced by a decrease of the intracellular pH during ischemia, and an increase of the intracellular calcium content during reperfusion after ischemia and during calcium repletion after calcium-free perfusion. These ultrastructural changes of the sarcolemma are, in our view, a consequence of the physiochemical behaviour of the sarcolemmal phospholipids.

Animals↗

PubMed1987

Isolation of protein components from rat lung lamellar bodies.

Lamellar bodies isolated from 10% (w/v) rat lung homogenates by discontinuous sucrose gradient centrifugation were shown to contain variable amounts of adhering proteins. These contaminating proteins could be removed by either Sepharose 4B gel filtration or precipitation of the crude preparation at pH 11.5. Both purification methods yielded membrane preparations with a phospholipid-to-protein ratio of 10.0 mumol/mg. Nearly complete separation of lamellar body phospholipid and protein could be achieved upon application of the purified membranes to DEAE-cellulose in the presence of 0.2% (v/v) Triton X-100. Phospholipid analyses showed that 83% of total lipid phosphorus was recovered in phosphatidylcholine. In phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine and phosphatidylinositol recoveries amounted to 4, 8, 2 and 2%, respectively. Molecular mass determinations of the isolated protein component of lamellar bodies by means of SDS polyacrylamide gel electrophoresis and staining with Coomassie brilliant blue revealed the presence of three protein bands with molecular masses of 64, 33 and 31 kDa. Upon staining with silver a 16 kDa protein was also visible. Sephadex G-100 gel filtration showed only one protein peak corresponding to a molecular mass of 64 kDa when protein was assayed with Coomassie brilliant blue.

Animals↗

PubMed1987

Physico-chemical properties and organization of lipids in membranes: their possible role in myocardial injury.

Lipids in biological membranes are organized in a bilayer configuration in order to form a semi-permeable barrier. The lipids are freely mobile in the bilayer, which is denoted as "fluid" or liquid-crystalline. For plasma membranes it is assumed that the lipids are not homogeneously distributed over the two leaflets or monolayers. This so-called lipid asymmetry is established for the erythrocyte membrane. There it was found that phosphatidylserine (PS) and phosphatidylethanolamine (PE) are present exclusively and predominantly in the cytoplasmic leaflet, respectively. It is shown that isolated PE at physiological conditions forms a non-bilayer configuration the so-called hexagonal HII phase. Moreover, isolated PS can undergo a transition from the fluid into the solid state upon addition of calcium. In mixtures of PS and PE, calcium is able to induce fusion events, possibly formation of the HII phase and phase separation of solid PS. The physico-chemical behaviour of these phospholipids will be discussed in the light of the structural changes of the sarcolemma of heart muscle cells observed by freeze-fracturing and thin section electron microscopy after ischaemia, ischaemia and reperfusion and the calcium paradox. The lateral phase separation of intramembranous particle aggregation is explained as isothermic phase separation by H+ and calcium. The disruption of the sarcolemma by the formation of blebs (liposomal structures) is interpreted as a destabilization of the bilayer configuration since PE prefers the HII phase and thus induces uncontrolled fusion events. This all leads to an irreversible disruption of the sarcolemma.

Animals↗

PubMed1987

Sarcolemmal destabilization and destruction after ischaemia and reperfusion and its relation with long-term recovery of regional left ventricular function in pigs.

This study investigated the relation between the extent of morphological damage, observed 2 hours after reperfusion which followed either 30 or 60 minutes of ischaemia, and the long-term recovery of regional myocardial function after the same periods of ischaemia. The nature of the morphological changes in this in vivo pig model is akin to that described in an in vitro Langendorff preparation. It is shown that sarcolemmal disruption, after 60 minutes of ischaemia followed by reperfusion, is associated with aggregation of sarcolemmal intramembranous particles and formation of multilamellar, lipidic structures suggesting a reorganization of the phospholipids, lateral phase separation and fusion events. However, thirty minutes of ischaemia with reperfusion did not lead to sarcolemmal disruption although extrusion of lipidic material, observed in a fraction of the mitochondria in each muscle cell, occurred independent of the duration of ischaemia. In another group of animals the regional myocardial function was assessed by cross-sectional echocardiography after 2 weeks of recovery. This correlated with the degree to which sarcolemmal integrity in the biopsies was maintained. The observed destruction of the sarcolemma was best explained in terms of bilayer destabilization, mediated by an increase in calcium and hydrogen ions in the cytosol of the myocardial cell.

Animals↗

PubMed1987

Loss of functional and structural integrity of the sarcolemma: an early indicator of irreversible injury of myocardium?

The purpose of this study was to explore the relationship between the extent of sarcolemmal damage observed 2 h after reperfusion of myocardium which had been ischemic for either 0.5 or 1 h and the long-term recovery of function of that same myocardium. For this purpose we studied the Ca2+ pumping ATPase activity and protein phosphorylation of sarcolemmal vesicles isolated after 2 h reperfusion. Both activities declined depending on the duration of ischemia, which suggests the development of sarcolemmal Ca2+ pump failure. Morphological examination of the sarcolemma by thin-section and freeze-fracture electronmicroscopy, in biopsies obtained after 2 h of reperfusion, showed severe clustering of intramembranous particles and formation and extrusion of lipidic liposomal structures which also depended on the duration of ischemia. Except for the occurrence of minor particle aggregation in the samples which had been ischemic for 0.5 h, sarcolemmal disruption was only seen in those myocardial segments which had been subjected to 1 h of coronary artery ligation. Recovery of regional myocardial function, assessed by 2-D-echocardiography after 2 weeks of reperfusion, was closely related to the degree to which sarcolemmal integrity was maintained after 2 h reperfusion.

Animals↗

PubMed1986

Cytofluorescence detection of adriamycin-mitochondria interactions in isolated, perfused rat heart.

The major side-effect of the anthracycline anti-tumor drug adriamycin is a specific, dose-dependent cardiotoxicity. Impairment of mitochondrial function has been suggested to play an important role in this toxicity. The present study addresses the question as to whether direct drug-mitochondria interactions occur in the isolated, perfused rat heart. To this aim, cytofluorescence microscopy experiments were performed on thin cryosections. To demonstrate the applicability of this technique it is shown that adriamycin bound to isolated rat liver and heart mitochondria can be visualized through its characteristic fluorescence. Longitudinal sections from heart tissue perfused with 50 microM adriamycin display two distinct cellular sites of drug accumulation, i.e., nuclei which exhibit very bright fluorescence and, in addition, mitochondria which become significantly labeled with the drug. The mitochondrial localization of adriamycin is confirmed independently by quantification of the drug content of the mitochondrial fraction after cell fractionation. These results are discussed in the light of the potential role of adriamycin-nuclei versus adriamycin-mitochondria interactions in the deterioration of heart performance.

Animals↗

PubMed1985

Ultrastructural changes of sarcolemma and mitochondria in the isolated rabbit heart during ischemia and reperfusion.

Isolated rabbit hearts were perfused by the Langendorff technique, made ischemic and subsequently reperfused. It was found that ischemia results in: (i) aggregation of the intramembranous particles in the sarcolemma and (ii) extrusion of pure lipidic multilamellar structures (liposomes) from swollen mitochondria. Subsequent reperfusion resulted in further aggregation of the sarcolemmal intramembranous particles and disruption of the sarcolemma, which was attended by the formation of liposome-like structures. Intramembrane particle aggregation is explained in terms of lateral phase separation of the membrane lipids and a reduction of repulsive forces between the membrane proteins, both induced by a decrease in pH and an increase in Ca2+ concentration intracellularly. The formation and extrusion of the multilamellar structures are discussed in terms of destabilization of the bilayer which results in a structural blebbing-off of pure lipid.

Animals↗

PubMed1985

Sarcolemmal disruption during the calcium paradox.

Reperfusion of an isolated heart with calcium-containing solution after a short period of calcium-free perfusion may result in irreversible cell damage (calcium paradox). The ultrastructure of the sarcolemma of the rabbit heart during the calcium paradox was studied by using fast freezing devices. This method excluded ultrastructural changes induced by chemical fixation and cryoprotection. In addition, thin-section and conventional freeze-fracture electron microscopy were used. During reperfusion with calcium-containing solution disruption of the sarcolemma was observed, which was attended with formation of unilamellar and multilamellar vesicles and aggregation of intramembrane particles. These ultrastructural changes are explained in terms of calcium- and proton-induced lateral phase separation and fusion processes in the lipid bilayer of the sarcolemma.

Animals↗

PubMed1980

Alpha-adrenergic blocking agents and the cardiovascular response to pharmacological doses of vasopressin.

The effects of alpha-adrenergic blockade with phentolamine or dibenamine on the cardiovascular response to pharmacological doses of vasopressin were studied in anesthetized dogs. Some observations were also made on the combined effects of vasopressin and norepinephrine. Changes in mean systemic arterial pressure, portal pressure, and resistance in the prehepatic splanchnic vasculature during vasopressin infusion were noted. A total of 97 dogs were used. alpha-Blockade appeared to enhance the response of arterial pressure to vasopressin, possibly because of loss of baroreceptor-mediated buffering action which normally attenuates its pressor action. Effects of vasopressin on mesenteric vascular resistance and portal pressure were unchanged or somewhat less after alpha-blockade, hence no evidence that its therapeutic effect would be improved by this combination. Vasopressin and norepinephrine when given together result in an additive pressor response with little or no evidence of potentiation.

Adrenergic alpha-Antagonists↗

PubMed1976

Splanchnic vascular responses to the infusion of prostaglandins A1, A2 and B1.

The effects of PGA1, PGA2 and PGB1 on the vasculature of the liver and small intestine were studied in 73 dogs. Infusions were made into a branch of the superior mesenteric artery, the hepatic artery, portal vein or femoral vein. They decreased systemic arterial pressure and dilated the hepatic arterial and prehepatic splanchnic (small intestinal) vascular beds, PGA being most active. Dilator response was not decreased by beta-adrenergic blockade. Compounds appear to be inactivated by liver and decreased systemic pressure less when infused directly into liver circulation. Dilator response was transient, particulary in small intestine, and abated or even converted to constriction when infusion was continued for a period of time. Intrahepatic portal venous vasculature appeared to be constricted by PGA.

Animals↗

PubMed1975

Hepatic, vascular and biliary responses to infusion of gastrointestinal hormones and bile salts.

The effects of secretin, cholecystokinin, synthetic pentagastrin, sodium dehydrocholate and sodium taurocholate on hemodynamics of the canine liver were studied in a total of 57 dogs. Bile flow was also measured. Dehydrocholate and cholecystokinin significantly decreased systemic arterial pressure while the other substances did not. Hepatic arterial vessels were dilated by pentagastrin and the bile salts; however, flow was not increased in the latter case. Intraheptic portal venous resistance was decreased by pentagastrin and increased by the bile salts. Portal flow was decreased by the bile salts and increased by pentagastrin. Apart from this, mean changes in portal venous flow and portal pressure were not statistically significant. All were potent choleretic agents except pentagastrin which produced only a relatively small transient increase in bile flow.

Animals↗