Biomedical subjects

O Moran

Publications and source records attributed to O Moran.

At least 37 records · Page 2Linked to original sources

PubMed1997

Simulation of action potential damping produced by anticonvulsant drugs.

Anticonvulsant drugs reduce the ability of central neurones to sustain high-frequency repetitive firing of action potentials. In recent years, it has been demonstrated that this effect is primarily due to a Na+ conductance reduction. We have simulated the electrical behaviour of a neurone, including Ca2+ and various K+ conductances. Although a reduction of Na+ conductance produces a progressive reduction until a complete suppression of the action potential bust, a smaller reduction of this conductance is necessary to produce the same effect when the delayed-rectifier K+ conductance and the Ca2+ conductance are concomitantly reduced . The results indicate that the drugs action on conductances other than Na+ is important for determining their anticonvulsant effect on neurones at therapeutic concentrations.

Action Potentials↗

PubMed1996

Modulation by protein kinase C activation of rat brain delayed-rectifier K+ channel expressed in Xenopus oocytes.

The modulation by protein kinase C (PKC) of the RCK1 K+ channel was investigated in Xenopus oocytes by integration of two-electrode voltage clamp, site-directed mutagenesis and SDS-PAGE analysis techniques. Upon application of beta-phorbol 12-myristate 13-acetate (PMA) the current was inhibited by 50-90%. No changes in the voltage sensitivity of the channel, changes in membrane surface area or selective elimination of RCK1 protein from the plasma membrane could be detected. The inhibition was mimicked by 1-oleoyl-2-acetyl-rac-glycerol (OAG) but not by alphaPMA, and was blocked by staurosporine and calphostin C. Upon deletion of most of the N-terminus a preceding enhancement of about 40% of the current was prominent in response to PKC activation. Its physiological significance is discussed. The N-terminus deletion eliminated 50% of the inhibition. However, phosphorylation of none of the ten classical PKC phosphorylation sites on the channel molecule could account, by itself or in combination with others, for the inhibition. Thus, our results show that PKC activation can modulate the channel conductance in a bimodal fashion. The N-terminus is involved in the inhibition, however, not via its direct phosphorylation.

Alkaloids↗

PubMed1996

Primary peritoneal serous papillary carcinoma: a study of 25 cases and comparison with stage III-IV ovarian papillary serous carcinoma.

The clinical characteristics and treatment outcome of patients with primary peritoneal serous papillary carcinoma (PPSC) (n = 22) was compared with stage III-IV papillary serous ovarian carcinoma (PSOC) patients (n = 63). There were no statistically significant differences between the PPSC and PSOC patients with regard to the mean age, menopausal status, parity, ascites fluid volume, proportion of stage IV disease, and the rate of optimal debulking achieved. The median disease-free interval was 15 and 18 months; the median survival was 21 and 26 months; and the 5-year survival was 18 and 24% for the PPSC and PSOC groups, respectively. The median survival time for patients with a residual tumor > or = 2 cm was 20.5 and 24 months, and for residual tumor > or = 2 cm was 46 and 41 months, in PPSC and PSOC patients, respectively. Survival was thus better, in both groups, when residual disease at the end of the operation was < 2 cm, though this was statistically significant only for PSOC (P < 0.02). We conclude that patients with PPSC should be treated as other stage II-IV PSOC patients. Combining optimal debulking with a platinum-based chemotherapy may offer the patient the most effective treatment.

Aged↗

PubMed1996

Accumulation of long-lasting inactivation in rat brain K(+)-channels.

We studied the phenomenon of cumulative inactivation in the voltage-dependent K+ channels of the Shaker-related subfamily Kv1 cloned from rat brain and expressed in Xenopus oocytes. In Kv1.4, repetitive stimulations at intervals shorter than 20 s produce cumulative inactivation even for brief stimuli that elicit K+ currents which do not show any significant decline during the depolarising pulse. These effects are absent or greatly reduced in the clones Kv1.1, Kv1.3, Kv1.5 and Kv1.6, and in the deletion mutant Kv1.4-delta-110, characterised by lack of "fast" (N-type) inactivation. We find that the inactivation caused by a single pulse increases after the pulse while the channels deactivate, and subsides with two time constants, indicating the existence of (at least) two inactivated states: IS, with a slow recovery kinetics and IF, with faster kinetics. In the simplest kinetic scheme accounting for our observations, IF is coupled sequentially to the open state O, while IS can be reached at a fast rate both from IF and from a pre-open, activated state, A, that is in fast equilibrium with O. The accumulation of long-lasting inactivation during the repolarisation is favoured by the prolongation of the lifetime of activated states due to the presence of IF. This explains the smaller accumulation effect observed in channels lacking fast inactivation. The physiological implications of these findings suggest how different channels of the Kv1 subfamily can affect differently the firing behaviour of neurones.

Animals↗

PubMed1996

Use dependence of tetrodotoxin block of sodium channels: a revival of the trapped-ion mechanism.

The use-dependent block of sodium channels by tetrodotoxin (TTX) has been studied in cRNA-injected Xenopus oocytes expressing the alpha-subunit of rat brain IIA channels. The kinetics of stimulus-induced extra block are consistent with an underlying relaxation process involving only three states. Cumulative extra block induced by repetitive stimulations increases with hyperpolarization, with TTX concentration, and with extracellular Ca2+ concentration. We have developed a theoretical model based on the suggestion by Salgado et al. that TTX blocks the extracellular mouth of the ion pore less tightly when the latter has its external side occupied by a cation, and that channel opening favors a tighter binding by allowing the escape of the trapped ion. The model provides an excellent fit of the data, which are consistent with Ca2+ being more efficient than Na+ in weakening TTX binding and with bound Ca2+ stabilizing the closed state of the channel, as suggested by Armstrong and Cota. Reports arguing against the trapped-ion mechanism are critically discussed.

Animals↗

PubMed1995

Properties of the Kv1.1 rat brain potassium channels expressed in mammalian cells: temperature effects.

We studied the temperature dependence of the currents mediated by potassium channels Kv1.1 cloned from rat brain expressed by permanent transfection in the human embryonic kidney cell line 292er. Voltage-gated outward currents, with a reversal potential near to the Nernst potential for potassium, were elicited by depolarising pulses. The currents activate fast and do not show inactivation during 50-ms test pulses. Increasing temperature decreased the amplitude of the currents, slowed the kinetics of activation and deactivation and shifted the activation curve to more negative potentials. We conclude that in Kv1.1 channels the closed states are associated with more ordered structure of the channel protein than the open state. The voltage-dependence and the kinetic properties are similar to those expressed in frog oocytes injected with cRNA coding the same Kv1.1.

Animals↗

PubMed1995

Inward rectifier potassium channels in plants differ from their animal counterparts in response to voltage and channel modulators.

We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related K+ channels in the plasma membrane of guard and root cells from Vicia faba and Zea mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H(+)-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg(2+)-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.

Animals↗

PubMed1995

Prediction of polypeptide secondary structures analysing the oscillation of the hydropathy profile.

The hydropathy profile of a polypeptide can reflect periodicity tightly linked, in particular, with alpha-helix and beta-strand conformations. We have developed an algorithm to detect such periodicity to predict the secondary structure of proteins. The method uses profiles constructed with the weighted average of hydropathy along the primary structure of the polypeptide and does the analysis of the variation of the profile for looking for periodic oscillations, using a variation detecting algorithm, without the definition of an empirical threshold. The independence of the method from known structures makes it particularly reliable for analysing membrane proteins.

Algorithms↗

PubMed1994

Proline mutations on the S4 segment of rat brain sodium channel II.

We have studied S4-proline mutants of the rat brain sodium channel II. In mutant A224P one proline was added on the S4 segment of repeat I, and in mutant P1313V a proline was removed from the segment S4 of the repeat II. In both mutants, the activation curve was shifted to more positive potentials, without changing the steepness of the voltage dependence. The time course of inactivation, consisting of two exponential components, was similar in the wild type and in mutant A224P. Differently, the decay of the current in mutant P1313V had only one component, with a time constant similar to that of the fast component of wild type channels. This change in kinetics was accompanied in mutant P1313V by a change in the voltage dependence of the apparent steady-state inactivation. We conclude that the addition or deletion of prolines in segment S4 does not affect significantly the activation of sodium channels, but alters their mode of inactivation.

Animals↗

PubMed1994

On the structure of mitochondrial porins and its homologies with bacterial porins.

By use of computer modelling, we have predicted a model of 16 transmembrane beta-strands for mitochondrial porins structure from human, Saccharomyces cerevisiae, Neurospora crassa and Dictyostelium discoideum. The proposed model takes into account biochemical and immunological data reported in the literature, as well as electrophysiological results obtained with yeast mitochondrial porins with mutations at selected amino acids. The predicted structure is very similar to that of some bacterial porins, as apparent from the homology of their hydropathic profiles.

Amino Acid Sequence↗

PubMed1994

Activation and deactivation properties of rat brain K+ channels of the Shaker-related subfamily.

We studied the activation properties of members of the Shaker-related subfamily of voltage-gated K+ channels cloned from rat brain and expressed in Xenopus oocytes. We find that Kv1.1, Kv1.4, Kv1.5, and Kv1.6 have similar activation and deactivation kinetics. The k+ currents produced by step depolarisations increase with a sigmoidal time course that can be described by a delay and by the derivative of the current at the inflection point. The delay tends to zero and the logarithmic derivative seems to approach a finite value at large positive voltages, but these asymptotic values are not yet reached at +80 mV. Deactivation of the currents upon stepping to negative membrane potentials below -60 mV is fairly well described by a single exponential. The decrease of the deactivation time constant at increasingly negative voltages tends to become less steep, indicating that this parameter also has a finite limiting value, which is not yet reached, however, at -160 mV. The various clones studied have very similar voltage dependencies of activation with half-activation voltages ranging between -50 and -11 mV and maximum steepness yielding and e-fold change for voltage increments between 3.8 and 7.0 mV. The shallower activation curve of Kv1.4 is likely to be due to coupling with the fast inactivation process present in this clone.

Animals↗

PubMed1994

Properties of the transient potassium currents in cerebellar granule cells.

Macroscopic potassium currents were studied in cell-attached and inside-out patches from rat cerebellar granule cells. They were related with transient IA type potassium channels. Currents activated rapidly at potentials higher than -40 mV and did not inactivate completely. The magnitude of the current diminished when the membrane patches were excised. No differences in the activation and inactivation properties were found between patches in the integral cells and cell free membrane patches. A biophysical description of the currents is presented.

Animals↗

PubMed1994

Outpatient endometrial sampling with the Pipelle curette.

This study compares outpatient endometrial sampling using the Pipelle endometrial sampling curette with conventional dilation and curettage (D&C) in patients with abnormal uterine bleeding. Endometrial sampling with the Pipelle curette was performed in 172 and D&C in 97 women. No complications were encountered with either of these procedures. One hundred and seventy (98.8%) of the Pipelle aspirations attempted were successfully completed. Sufficient material for histological assessment was obtained in 154 (90.6%) of the women who underwent Pipelle endometrial sampling and in only 66 (68%) of those who underwent D&C (p < 0.0001). In postmenopausal women, adequate specimens were obtained in 74 of 88 (84.1%) by Pipelle and in only 22 of 48 (45.8%) by D&C. In 45 cases the histologic diagnosis of the endometrium obtained by Pipelle sampling was compared with the one of endometrium obtained by D&C or hysterectomy performed shortly thereafter. The diagnosis was identical in 43 (95.5%) cases. Endometrial sampling with the Pipelle was well tolerated causing occasionally only slight discomfort.

Ambulatory Surgical Procedures↗

PubMed1993

Currents activated by GABA and their modulation by Zn2+ in cerebellar granule cells in culture.

Whole-cell and single-channel currents evoked by gamma-aminobutyric acid (GABA) were recorded from rat cerebellar granule cells in culture. The electrophysiological properties of these currents were studied in control condition and in the presence of external Zn2+ (10-30 microM). GABA (10 microM) induced bicuculline-sensitive whole-cell currents which desensitized. The desensitization was more rapid for higher concentrations of GABA (30-300 microM). The current-voltage relation of GABA currents was linear from -70 to +50 mV. Two different types of cells were found with respect to the stoichiometry for agonist binding, one with Hill coefficient 1.5 and another one with coefficient 1. The half-maximum concentration displayed more variability, with values varying from 10 to 50 microM. The time constant of recovery from desensitization (tau r) was estimated to be 36 s. Zn2+ (30 microM) blocked GABA-activated whole-cell currents in a non-competitive and voltage-independent way without a significant change in the current kinetics. In excised outside-out patches, GABA (0.5 microM) activated single-channel events of 19 and 31 pS. Kinetic analysis yielded two mean shut times (tau c1 = 2.70 ms, tau c2 = 205 ms) and one mean open time (tau o = 3.64 ms). Zn2+ (10 microM) did not affect single-channel conductances and mean open and shut times, but significantly reduced the probability of opening from 0.17 to 0.06. It is probable that Zn2+ binds to a site located on the extracellular part of the GABAA receptor channel complex.

Animals↗

PubMed1993

Modulation of voltage-dependent calcium channels by glutamate in rat cerebellar granule cells in culture.

Voltage-dependent calcium channels of cerebellar granule cells maintained in a Ca(2+)-free depolarising solution were recorded using the cell-attached configuration of the patch-clamp technique. An increase in the maximum open probability of calcium channels and a shift in their activation curve toward more hyperpolarizing potentials were found in the presence of glutamate, a natural, excitatory amino acid. Such an increase in the activity of calcium channels was not due to ionic fluxes activated by glutamate, and was probably produced by a second messenger pathway triggered by the binding of glutamate to its receptor.

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

PubMed1993

Channels in mitochondrial membranes: knowns, unknowns, and prospects for the future.

Rapid diffusion of hydrophilic molecules across the outer membrane of mitochondria has been related to the presence of a protein of 29 to 37 kDa, called voltage-dependent anion channel (VDAC), able to generate large aqueous pores when integrated in planar lipid bilayers. Functional properties of VDAC from different origins appear highly conserved in artificial membranes: at low transmembrane potentials, the channel is in a highly conducting state, but a raise of the potential (both positive and negative) reduces drastically the current and changes the ionic selectivity from slightly anionic to cationic. It has thus been suggested that VDAC is not a mere molecular sieve but that it may control mitochondrial physiology by restricting the access of metabolites of different valence in response to voltage and/or by interacting with a soluble protein of the intermembrane space. The latest application of the patch clamp and tip-dip techniques, however, has indicated both a different electric behavior of the outer membrane and that other proteins may play a role in the permeation of molecules. Biochemical studies, use of site-directed mutants, and electron microscopy of two-dimensional crystal arrays of VDAC have contributed to propose a monomeric beta barrel as the structural model of the channel. An important insight into the physiology of the inner membrane of mammalian mitochondria has come from the direct observation of the membrane with the patch clamp. A slightly anionic, voltage-dependent conductance of 107 pS and one of 9.7 pS, K(+)-selective and ATP-sensitive, are the best characterized at the single channel level. Under certain conditions, however, the inner membrane can also show unselective nS peak transitions, possibly arising from a cooperative assembly of multiple substrates.

Amino Acid Sequence↗

PubMed1993

Cytologic examination of ovarian cyst fluid for the distinction between benign and malignant tumors.

OBJECTIVE: To assess the feasibility of using cytologic examination of ovarian cyst fluid for distinguishing between benign and malignant tumors. METHODS: Cyst fluid was aspirated at surgery in 83 women with benign and 35 women with malignant (25 invasive and ten borderline) ovarian tumors and submitted for routine cytologic examination. RESULTS: The specificity of the cytologic examination was 100%, but the sensitivity and negative predictive value were only 26 and 76%, respectively. CONCLUSION: The low sensitivity and negative predictive value of cytologic cyst fluid examination preclude its use for the distinction between benign and malignant ovarian tumors.

Adolescent↗

PubMed1993

Cyst fluid CA 125 levels in ovarian epithelial neoplasms.

OBJECTIVE: To assess the feasibility of using cyst fluid CA 125 levels to distinguish between benign and malignant ovarian cystic neoplasms. METHODS: CA 125 levels were measured in ovarian cyst fluid and in serum obtained at surgery in 44 women with ovarian cystic tumors of epithelial origin (25 benign, 12 malignant, and seven borderline). RESULTS: The median cyst fluid CA 125 level in malignant neoplasms (671 U/mL) was higher than in benign tumors (175 U/mL), and 86% of the malignant tumors contained levels higher than 100 U/mL in the cyst fluid, compared with only 62% of the benign tumors. However, these differences were not statistically significant. CONCLUSION: Cyst fluid levels of CA 125 cannot be used to distinguish between benign and malignant ovarian cysts of epithelial origin.

Adolescent↗