Biomedical subjects

C Maldonado

Publications and source records attributed to C Maldonado.

At least 55 records · Page 3Linked to original sources

PubMed1995

Intracellular localization of the testicular and sperm-specific lactate dehydrogenase isozyme C4 in mice.

The proposed dual intracellular distribution of the sperm-specific lactate dehydrogenase (EC 1.1.1.27) isozyme C4 (LDH C4) has been based on indirect evidence. In order to obtain direct evidence on the localization of this LDH isozyme in mice, postembedding immunocytochemistry at ultrastructural level was performed on testes, epididymal spermatozoa, and isolated testicular mitochondria. The immunogold technique was applied to thin sections incubated first in partially purified specific anti-LDH C4 rabbit IgG, and immunoreactive sites were detected with colloidal gold adsorbed to anti-rabbit IgG. In the testis, immunostaining was found in the cytoplasm of spermatocytes and spermatids and in the principal and middle pieces of differentiating spermatozoa. Spermatozoa from epididymis also exhibited heavy labeling of colloidal gold in their middle and principal pieces, but the immunostaining was weak in the special type of mitochondria present in spermatocytes, spermatids, and spermatozoa (sperm-type mitochondria, STM). The isolation of STM produced several morphological changes in comparison with those in situ, including an enhancement of the LDH C4 labeling in the mitochondrial matrix. The other type of mitochondria (non-STM) from spermatocytes and nonspermatogenic cells were not immunostained and served as background control. The results presented here confirm previous findings, gathered by indirect methods, indicating a dual localization of LDH C4 in the cytosol of spermatocytes, spermatids, and spermatozoa, as well as in the matrix of sperm-type mitochondria.

Animals↗

PubMed1995

Transseptal defibrillation is superior for transvenous defibrillation.

The conventional electrode configuration of current internal defibrillation systems most commonly use superior vena caval (SVC) or combined SVC and subcutaneous (SC) electrodes as anode, and right ventricular apex (RVA) electrode as cathode. We have demonstrated earlier that the septal mass is important for defibrillation. The purpose of the present study was to compare a transseptal to a conventional electrode arrangement in the canine model. Three endocardial electrodes, 5 French EnGuard were positioned in RVA, SVC, and the right ventricular outflow (RVO) in eight dogs. A 5 French SC electrode was positioned in the fifth left intercostal space. RVA-RVO-/SC+ (configuration 2) was compared to SVC-SC+/RVA- (configuration 1). Defibrillation threshold testing was performed using asymmetrical biphasic shock, 6 msec+/2 msec-. Probit fit was used to compare the results at 40%, 50%, 60%, and 90% probabilities, and the logistic regression analysis to estimate the impact of variables. Electrode configuration had the strongest predictive value. Configuration 2 was superior to configuration 1 (P = 0.0016). At any voltage settings the probability of success for configuration 2 was greater, and current less (P < 0.00005). The energy requirements were reduced by approximately 33% for configuration 2. There were no significant differences in impedance between the two configurations. We conclude that transseptal defibrillation is more effective because of the improved lead geometry and voltage gradient.

Animals↗

PubMed1995

Electrode surface area is an important variable for defibrillation.

Previous studies have established efficacy of transseptal defibrillation. The purpose of the present study was to evaluate the role of transvenous electrode surface area for defibrillation. Sixteen dogs were randomized to 8 French and 5 French EnGuard electrodes; 8 dogs in each group. The length of the defibrillation coils was identical for both, but the surface area was different due to differences in the electrode diameters. Defibrillation threshold (DFT) testing was performed using a biphasic shock waveform, 6 msec+/2msec-. Logistic regression analysis was used to determine if the probability of defibrillation adjusted for voltage, current, and energy was different for 8 French electrodes. Logistic regression analysis found significant differences between 8 French and 5 French electrodes, with less voltage (P < 0.005), current (P < 0.03), and energy (P < 0.001) required at any level of probability to defibrillate for 8 French electrodes. These results support the conclusion that the surface area for endocardial electrodes is a significant factor for defibrillation. Therefore, when designing endocardial electrodes a desirable objective of reducing the electrode size should be weighed against the need to minimize DFTs.

Animals↗

PubMed1994

Membrane fluidity of microsomal and thymocyte membranes after X-ray and UV irradiation.

A brief literature review shows that ionizing radiation in biological membranes and in pure lipid membranes causes malondialdehyde formation, indicating lipid peroxidation processes. With respect to membrane fluidization by ionizing radiation, in pure lipid membranes rigidization effects are always reported, whereas contradictory results exist for biological membranes. Starting from the assumption that membrane proteins at least partly compensate for radiation effects leading to a rigidization of membrane lipid regions, pig liver microsomes, as a representative protein-rich intracellular membrane system, were irradiated with X-rays or UV-C with doses up to 120 Gy at a dose rate of 0.67 Gy min-1 and up to 0.73 J cm-2 at an exposure rate of 16.2 mJ cm-2 min-1, respectively. For both irradiation types a weak but significant positive correlation between malondialdehyde formation and membrane fluidity is revealed throughout the applied dose ranges. We conclude that the membraneous protein lipid interface increases its fluidity under radiation conditions. Also, thymocyte ghosts showed an increased fluidity after X-ray irradiation. Fluidity measurements were performed by the pyrene excimer method.

Animals↗

PubMed1994

Marked action potential prolongation as a source of injury current leading to border zone arrhythmogenesis.

The objective of this study was to delineate electrophysiologic phenomena in a border zone adjacent to a zone of marked action potential prolongation. By means of a standard microelectrode technique, we studied sheep Purkinje fibers placed in a partitioned chamber and superfused with Tyrode's solution. Ethylenediamine tetraacetic acid (EDTA) was added to one chamber. Recordings were made in the abnormal segment (ABN) superfused with EDTA and at two sites in the normal segment (NL)--at the border within 0.5 mm (NL-B) and 3 to 4 mm from the partition (NL-D). Exposure of ABN to EDTA caused marked prolongation of the action potential duration (APD) and triggered activations (TAs), which were found to have the earliest recorded activation at NL-B (n = 20), at ABN (n = 8), or at both sites (n = 12). NL-B recordings displayed prolonged low-amplitude secondary plateaus, which were termed "border zone early afterdepolarizations." These were coincident with the plateaus of the prolonged action potentials in ABN and appeared to be due to electrotonic transmission of current from ABN to NL-B. Border zone TAs arose from these low-amplitude plateaus and were either eliminated by the addition of lidocaine to NL consistent with their presumed NL site of origin or occurred after localized withdrawal of EDTA from one segment in fibers rendered quiescent at the plateau by generalized superfusion with EDTA. In conclusion, APD and membrane potential inhomogeneities lead to electrotonic transmission of injury current to border zones adjacent to zones of abnormal APD prolongation. This injury current leads to TAs originating at the border zone. These findings may be relevant to the role of injury current in clinical arrhythmias.

Action Potentials↗

PubMed1994

Brevetoxin-3 (PbTx-3) inhibits oxygen consumption and increases Na+ content in mouse liver slices through a tetrodotoxin-sensitive pathway.

To have insights into possible non-neural effects of PbTx-3 (0.07 microgram/ml), its effects on various parameters of hepatic metabolism were evaluated. PbTx-3 inhibits oxygen consumption (QO2) in liver slices by 25 +/- 1%, and increases hepatocyte Na+/K+ ratio by 72 +/- 4%. Ouabain, a Na(+)-K(+)-pump inhibitor, also reduced QO2 by 19 +/- 2% and raised the Na+/K+ ratio by 77 +/- 4%. The effects of PbTx-3 and ouabain on QO2 and Na+/K+ ratio were not additive, suggesting a role for the Na(+)-K(+)-pump in these actions of PbTx-3. However, Na(+)-K(+)-pump activity determinations, using 86Rb as a K+ tracer, did not reveal inhibitory effects of this toxin on the transport system. This indicates that the pump is not a target of PbTx-3. The effect of PbTx-3 on liver slices Na+ content was abolished by the sodium channel blocker tetrodotoxin (0.1 microM). Tetrodotoxin also antagonized the inhibition of oxygen consumption by PbTx-3. These results suggest that in the liver PbTx-3 can induce effects that appear to be similar to those observed in excitable tissue.

Analysis of Variance↗

PubMed1994

Role of junctional zone cells between Purkinje fibres and ventricular muscle in arrhythmogenesis.

OBJECTIVE: The aim was to examine under abnormal conditions the flow of currents across junctional (J-) cells found between Purkinje fibre cells and ventricular muscle cells, and determine whether these currents play a role in increasing the excitation rate of ventricular muscle. METHODS: Canine Purkinje fibre and papillary muscle preparations were mapped to locate the Purkinje fibre-ventricular muscle cell junction (PVJ). Using standard techniques, action potentials from Purkinje fibres, J-cells, and ventricular muscle cells and extracellular electrograms were simultaneously recorded at the PVJ. The tissue was then superfused with Tyrode solution plus 4.5-5.0 mmol of ethylenediamine tetra-acetate (EDTA). RESULTS: EDTA prolonged the action potential duration mainly in Purkinje fibres. Secondary plateaus were recorded at membrane potentials of -63.5(SD 7.6) mV (n = 16) in J-cells, and at membrane potentials of -74.9(4.3) mV (n = 9) in ventricular muscle cells. Triggered activations appeared on both secondary plateaus with the earliest site of activation at J-cells (n = 12), at ventricular muscle cells (n = 4), or in both (n = 6). Tetrodotoxin (3-9 x 10(-7) M) and verapamil (1 x 10(-6)-10(-5) M) suppressed triggered activations. CONCLUSION: The PVJ zone appears to be an important site for the generation of triggered activations. Interventions suggest that triggered activations originating in the J-cell depend on delayed repolarisations which trigger the activation of sodium and/or calcium channels.

Action Potentials↗

PubMed1993

A prospective randomized trial of Novoste right versus Judkins catheters for engagement of the right coronary artery during diagnostic catheterization.

There has been little technical advancement in catheter shape for diagnostic cardiac catheterization since the early reports of Sones and colleagues during the development of the procedure. In order to determine the utility of a new catheter that directly, without torque or rotation, engages the right coronary artery (RCA), one hundred patients were randomized between 6Fr standard RCA Judkins (6Fr R4) (Cordis Corporation, Miami, FL, USA) or 6Fr Novoste RCA catheters (Novoste Corporation, Aguadilla, Puerto Rico). Endpoints included the duration of the various aspects of the procedure and a qualitative and quantitative assessment of angiographic quality. The Novoste RCA catheters were associated with statistically decreased times of catheter insertion (42 +/- 37 vs 90 +/- 119 secs), and engagement (31 +/- 35 vs 77 +/- 117 secs), of the right coronary artery as compared to Judkins catheters. Judkins RCA catheters had a significantly higher primary success rate (96%) than the Novoste group (84%, P = 0.045). There was no difference in angiographic quality in either group and no complications occurred during the study. While taller patients (mean 68 in) had increased success with the Novoste catheter, no other clinical, demographic, or anatomical characteristics of the RCA orifice predicted successful engagement and angiography. The direct engagement Novoste RCA catheter is associated with a more expeditious procedure than Judkins catheters when they can engage the RCA orifice. However, Novoste catheters were less successful and required more frequent exchanges to complete the procedure.

Adult↗

PubMed1992

A flow-cytometric method to study DNA fragmentation in lymphocytes.

A method to measure DNA fragmentation cell by cell in a cell population was implemented based on acridine orange procedure to determine DNA content of single cells by flow cytometry. Using this method it can be observed that the fragmentation process induced by irradiation in thymic cells occurs in a fraction of the population, thus indicating that this process is not evenly distributed over the total population, and that it corresponds to a fast phenomenon in which the cells suddenly lose DNA material.

Acridine Orange↗

PubMed1992

Ultrastructural and immunocytochemical study of the myoendocrine cells of the fish Hypostomus cordovae.

The myoendocrine cells of the heart of Hypostomus cordovae (Günther 1880), a teleost fish from South America, were investigated by electron microscopy and immunohistochemistry. By applying antibodies raised against synthetic cardiodilatin 99-126 (CDD/ANP 99-126), a specific labeling of this hormone was found in the heart of this fish, mainly in myoendocrine cells of atrial trabeculae, where specific secretory granules are stored. The distribution of secretory granules exhibited striking seasonal variations. In winter there were fewer differentiated myoendocrine cells, which were easily recognized by the presence of specific secretory granules, most of which occur clustered in perinuclear areas of the cells. By contrast, in summer the majority of the myocardic cells of the atrium are active endocrine cells. They contain abundant secretory granules widely scattered in the cytoplasm, many of them polarized toward the subendocardial aspect of the cell. The secretory granules can be easily differentiated from the Weibel-Palade granules of endothelial cells, the shape, size and content of which were typical at electron-microscopic level. In addition, these endothelial granules did not display CDD immunoreactivity. The presence of cardiodilatin in a fish such as Hypostomus cordovae further supports the view that cardiac hormones are present in many Vertebrates and may preserve analogous roles such as those reported in other species throughout the group.

Animals↗

PubMed1992

Conduction of early afterdepolarizations in sheep Purkinje fibers and ventricular muscle. An in vitro arrhythmia model.

To establish an arrhythmia generator model, a double-chambered bath was used in which sheep Purkinje fibers (PF) and ventricular muscle (VM) were placed. The conduction patterns of early afterdepolarization-induced triggered activations (TAs) were examined between normal segments bathed in unmodified Tyrode solution and abnormal segments bathed in ethylenediaminetetraacetate (3.3-5.0 mmol). Three types of preparations were used: PF-PF (n = 10), VM-VM (n = 5), and PF-VM (n = 13). Two types of spontaneous TAs appeared. One type was conducted to normal segments, inducing activations over the entire preparation, while the other type was not conducted. The conducting TAs had significantly more rapid mean dV/dt, larger amplitude, and higher peak transmembrane voltage as compared to nonconducting TAs. While conduction occurred in all PF-PF, VM-VM, and PF-VM preparations, conduction of TAs from abnormal segment VM to normal segment PF was impaired. A low plateau resulting from electrotonic transmission of depolarizing current from abnormal segments was recorded in normal segments near the border. This low plateau probably facilitated the transmission of TAs. In addition to spontaneous TAs, stimulated or spontaneous action potentials from NL were conducted to the not yet fully repolarized ABN and induced activations resembling TAs. These results may be relevant to clinical arrhythmias due to action potential prolongation. The arrhythmia may occur directly as a result of triggered activity or indirectly via slow conducting TAs, creating the possibility for reentry. This type of model may be useful for intervention studies, for example, by identifying agents that block abnormal segment to normal segment conduction.

Action Potentials↗

PubMed1992

Role of protein kinase-C in thymocyte apoptosis induced by irradiation.

The role of protein kinase C in radiation-induced death of thymocytes was studied. For this purpose murine thymocytes were irradiated and incubated for 6 h at 37 degrees C and afterwards the fraction of fragmented DNA was measured. Results indicate that radiation-induced DNA fragmentation can be prevented by adding the protein kinase C inhibitor H-7 or staurosporine to the thymocytes during incubation time. Incubation of irradiated cells with HA-1004, an inhibitor of cAMP-dependent protein kinase, with a minor effect on protein kinase C did not affect the DNA fragmentation induced by irradiation. Incubation of cells with phorboldibutyrate gave a dose-dependent induction of DNA fragmentation. This effect can be inhibited by staurosporine. These results suggest that radiation-induced DNA fragmentation is an active cellular process in which protein kinase C plays an important role.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1992

Purkinje fibre-papillary muscle interaction in the genesis of triggered activity in a guinea pig model.

OBJECTIVE: Previous studies have attempted to characterise the genesis of triggered activity related to early afterdepolarisations. Little is known about their conduction behaviour. This study was designed to examine the origin and conduction behaviour of triggered activations to throw light on the pathogenesis of torsade de pointes. METHODS: Electrophysiological interactions related to triggered activations and early afterdepolarisations between papillary muscle and Purkinje fibres were studied in the guinea pig in a single chambered bath. EDTA (5 mM) in Tyrode's solution was used and microelectrodes were placed in both papillary muscle and Purkinje fibres. RESULTS: During early superfusion, marked prolongation of action potential duration and early afterdepolarisations occurred in Purkinje fibres but not in papillary muscle. In addition: (1) with prolongation of action potential duration and early afterdepolarisations in Purkinje fibres, triggered activations arose during phase 2 and were conducted to papillary muscle, where they induced activations; (2) the number of papillary muscle discharges increased with the increase in Purkinje fibre action potential duration in a linear correlation; (3) severing a segment of papillary muscle from Purkinje fibres eliminated these papillary muscle activations; (4) some triggered activations did not conduct to papillary muscle; these had smaller amplitude, slower rate of depolarisation (dV/dt), more positive activation voltage, and similar peak voltages compared to conducted triggered activations; (5) a low plateau resulting from electrotonic interaction was recorded at the Purkinje fibre-papillary muscle junction; this plateau may have facilitated conduction of triggered activations. CONCLUSIONS: In this preparation there was a disparity of effect on Purkinje fibre and papillary muscle. Prolongation of action potential duration and repetitive activations due to early afterdepolarisations originated in Purkinje fibres and were conducted to papillary muscle. Purkinje fibre-papillary muscle interactions are of interest in relation to torsade de pointes arrhythmias which are believed to arise from this mechanism.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1992

Differentiation of endocrine myocardiocytes in the developing heart of the toad (Bufo arenarum Hensel).

The differentiation of endocrine myocardiocytes was investigated in the heart of developing toad Bufo arenarum Hensel, combining ultrastructural and immunocytochemical procedures. The distribution of immuno-reactive atrial natriuretic peptide (ANP) in the whole heart was appraised by light microscopy, applying biotin-streptavidin and immunofluorescence techniques. With the latter procedures ANP was first recognized at embryonic stage 22, in both atrium and ventricle. In the ensuing stages the ANP-reactivity became stronger in the atrium, while it became dimmer in the ventricle. At the end of the larval prometamorphic stage, atrial myocardiocytes acquired almost all the features of adult myoendocrine cells. At electron microscope level, small inclusions, about 110-120 nm in diameter, resembling secretory granules were found in myoendocrine cells beginning at embryonic stage 22. However, no immunogold labeling of ANP occurred until stage 25. The number of secretory granules diminished in the ventricles and increased in the atrium of the larval heart and at the end of the prometamorphic stage the atrial myoendocrine cells presented the ultrastructural characteristics of active secretory cells. The synthesis of ANP in larvae is enhanced at a critical period of development when the developing toad switches from an aquatic environment to terrestrial life. The cardiac hormones seem to play a key role in the regulation of the osmolarity of body fluids at this developmental stage.

Animals↗

PubMed1991

Radiation-induced surface IgG modulation: protein kinase C involvement.

Although radiation-induced loss of surface IgG (s-IgG) expression on murine B cells is known to be dependent on intact energy metabolism and integrity of the cytoskeleton, the exact mechanism of this radiation effect is not known. Evidence reported here shows that inhibition of protein kinase C (PKC) by H-7 impairs the radiation-induced s-IgG modulation, whereas addition of HA-1004, which preferently inhibits c-AMP-dependent protein kinase, shows only minor effects. On the other hand PMA, a PKC activator, mimics the radiation effect, and H-7 but not HA-1004 inhibits the PMA-induced loss of s-IgG expression. Therefore it is suggested that PKC is involved in the modulation of s-IgG induced by irradiation on B cells. The possibility of membrane participation in this event is discussed.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1991

Defibrillation efficacy using two low-profile endocardial electrodes.

The hypothesis that improved energy delivery and defibrillation efficacy can be achieved by using two widely separated endocardial electrodes and a cutaneous patch electrode was explored by positioning two 6.5 F electrodes (NuMed, Hopkinton, New York) with 5 cm platinum-iridium coils in the right ventricular apex (RVA) and the right ventricular outflow (RVO) in eight dogs. In another 12 dogs, an additional electrode was positioned in the RVA. A cutaneous patch (P) was placed at the cardiac apex. Biphasic pulses were delivered, the first pulse (6 ms) positive, the second negative (2 ms). The leading edge of the second was equal to the trailing edge of the first. RVO-/P+ and RVA-RVO-/P+ were compared with RVA-/P+ at a constant voltage setting required to achieve a 60% probability of success (P60) for RVA-/P+. At a constant voltage output, the probability of success for RVA-RVO-/P+ was significantly higher (81%) than RVO-/P+ (60%) or RVA-/P+ (67%) (p less than 0.03). The current delivered was greater for RVA-RVO-/P+ (9.9 +/- 2.3 amps) than for either RVA-RVO-/P+ (8.7 +/- 1.9 amps) or RVO-/P+ (9.0 +/- 2.0 amps) (p less than 0.0001). Similarly, the impedance was significantly lower for RVA-RVO-/P+ (66 +/- 12 omega) than for RVA-/P+ (75 +/- 12 omega) and RVO-/P+ (72 +/- 9.6 omega) (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Effects of stress and beta 1 blockade on the ventricular depolarization gradient of the rate modulating pacemaker.

Prism-CLR is a closed loop, rate modulating pacemaker that uses ventricular depolarization gradient (Gd) to continuously adjust heart rate. Heart rate response to a formal mental stress protocol, esmolol (500 mcg/kg bolus, 75-125 mcg/kg/min infusion), and mental stress during esmolol infusion were studied in six patients to investigate if Gd and paced heart rate response are under direct beta-adrenergic control. Paced heart rates increased in response to mental stress in a physiological manner (P less than 0.001). Response to esmolol infusion was paradoxical, with increased paced heart rates during esmolol bolus and infusion (P less than 0.05). There was no significant alteration in either systolic or diastolic blood pressure during mental stress or esmolol infusion (P greater than 0.05). Paradoxical increase in paced heart rates during esmolol administration suggests a primary or secondary effect of esmolol to decrease the ventricular depolarization gradient. This hypothesis was supported in four dog studies in which direct Gd measurements were made during esmolol infusion. Mental stress during esmolol infusion resulted in significantly increased paced heart rates (esmolol effect) with blunted changes in heart rate in response to the mental stress. The results of this study suggest that the physiological rate response during mental stress is attributable to sympathetic autonomic response.

Adrenergic beta-Antagonists↗

PubMed1990

Protein kinase-C involvement in thymocyte apoptosis induced by hydrocortisone.

The involvement of protein kinase-C in thymocytes death induced by hydrocortisone was studied. Thymus cells were incubated 6 hr or in the presence of hydrocortisone, labeled with Acridine orange, and the DNA content of each nuclei was estimated by cytofluorimetry. The results indicate that hydrocortisone-induced DNA fragmentation can be prevented by adding the protein kinase-C inhibitor H-7 to the cell suspension. Incubation of the H-A 1004, an inhibitor of c-AMP-dependent protein kinase, with low effect on on protein kinase-C, did not interfere with the cortisone-mediated DNA fragmentation. Therefore, it can be concluded that protein kinase-C plays an important role in the process of lympholysis mediated by corticoids.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗