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M J Morales

Publications and source records attributed to M J Morales.

34 records · Page 2Linked to original sources
PubMed1995

Time- and voltage-dependent modulation of a Kv1.4 channel by a beta-subunit (Kv beta 3) cloned from ferret ventricle.

In mammals, voltage-gated K+ channels can be made of complexes containing alpha-subunits similar to the Shaker K+ channel and smaller cytoplasmic beta-subunits. Recent studies have suggested that these ancillary beta-subunits can modulate K+ channel gating properties. We studied the effects of a K+ channel beta-subunit, Kv beta 3, coexpressed with a Kv1.4 alpha-subunit, FK1, on the time and voltage dependence of channel activation, inactivation, recovery from inactivation, and deactivation, using an oocyte expression system. Kv beta 3 was found to accelerate both the fast and the slow component of Kv1.4 inactivation. Kv beta 3 also altered the relative contributions of the two components of inactivation by increasing the contribution of the slow component to the inactivation process. Kv beta 3 slowed recovery from inactivation for Kv1.4, but not for a Kv1.4 deletion mutant lacking N-type inactivation. Finally, steady-state activation and the time course of Kv1.4 current activation were not strongly influenced by Kv beta 3; however, deactivation was slowed in the presence of Kv beta 3. This study suggests that Kv beta 3 alters channel states which follow activation.

Animals↗
PubMed1994

Cloning and characterization of an Ito-like potassium channel from ferret ventricle.

FK1, a ferret ventricular full-length cDNA clone, encodes a 654-amino acid protein with 98% identity to human K+ transient outward current (Ito)-like HK1 (Tamkun et al. FASEB J.5: 331-337, 1991). FK1 is detectable in ferret brain, atrium, left and right ventricle, and kidney but not in skeletal muscle, endothelial cells, aorta, and liver. In Xenopus oocytes, FK1 cRNA gives rise to a rapidly activating and inactivating Ito-like current, which is highly K+ selective (Na(+)-to-K+ permeability ratio = 0.003). Activation occurs over an approximately 50-mV range (-40 to +10 mV) and displays a sigmoid delay in onset with potential-dependent time constants that decrease with depolarization. Steady-state activation can be described with either a simple Boltzmann relationship [half-activation potential (V1/2) = -25 mV, slope (k) = 10 mV] or a Boltzmann relationship raised to either the third or fourth power (alpha 3: V1/2 = -43 mV, kappa = 13.1 mV; alpha 4: V1/2 = -48 mV, kappa = 13.6 mV, where alpha is the activation variable). Inactivation kinetics are biexponential, with the main fast time constant becoming independent of membrane potential depolarized to 0 mV. Steady-state inactivation can be described with a single Boltzmann relationship (V1/2 = -57 mV, kappa = 5.0 mV). Fast inactivation is removed by NH2-terminal deletions. Recovery from inactivation (-90 mV) is quite slow (half-time = 4.8 +/- 2.5 s). In 2 mM extracellular K+ concentration ([K+]o), FK1 tail currents display conventional deactivation behavior; however, in 98 mM [K+]o the tail currents display "reopening" behavior. These results suggest a molecular basis for the electrophysiological similarities between ferret and human ventricular Ito (Campbell et al. J. Gen. Physiol. 101: 571-601, 1993; Näbauer et al. Circ. Res. 73: 386-394, 1993).

Amino Acid Sequence↗
PubMed1993

A polymerase chain reaction-based method for detection and quantification of reporter gene expression in transient transfection assays.

Transcription in higher eukaryotes is often studied by the use of transient transfection assays. These experiments are performed by cloning putative cis-acting transcriptional elements (i.e., a promoter or enhancer) with a reporter gene that codes for a protein not expressed by the target cells. Although this approach is useful in many cases, the limited sensitivity of reporter assays can prevent studies in cases where few cells are obtainable or efficiency of transfection is low. We present an alternative approach. Cells are transfected with a plasmid containing a promoter with a human growth hormone (hGH) reporter gene. After an incubation period, RNA is isolated, and DNA complementary to the growth hormone mRNA is produced. The reporter cDNA concentration is measured by quantitative polymerase chain reaction (PCR). We have designed PCR primers that span the mRNA splice sites of the human growth hormone gene; these ensure exclusive amplification of the hGH cDNA and not the reporter plasmid. The assay is sensitive and simple to perform, requires no special equipment, and can quantify reporter cDNA concentration over a broad range.

Base Sequence↗
PubMed1992

A 105-kDa protein is required for yeast mitochondrial RNase P activity.

RNase P from the mitochondria of Saccharomyces cerevisiae was purified to near homogeneity > 1800-fold with a yield of 1.6% from mitochondrial extracts. The most abundant protein in the purified fractions is, at 105 kDa, considerably larger than the 14-kDa bacterial RNase P protein subunits. Oligonucleotides designed from the amino-terminal sequence of the 105-kDa protein were used to identify and isolate the 105-kDa protein-encoding gene. Strains carrying a disruption of the gene for the 105-kDa protein are viable but respiratory deficient and accumulate mitochondrial tRNA precursors with 5' extensions. As this is the second gene known to be necessary for yeast mitochondrial RNase P activity, we have named it RPM2 (for RNase P mitochondrial).

Amino Acid Sequence↗
PubMed1991

Corticosteroid-induced growth hormone secretion in normal and obese subjects.

OBJECTIVE: In normal subjects, corticosteroids stimulate growth hormone (GH) secretion at 3 hours. Obesity is associated with blunted GH secretion. In order to clarify both the deranged mechanism of GH secretion in obesity and the corticosteroid mechanism of action we have assessed in normal and obese subjects the effects of dexamethasone, pyridostigmine (a drug capable of suppressing somatostatin release) and GHRH. We also compared in normal subjects the stimulatory effect of three different corticosteroids on plasma GH levels. DESIGN: In both normal and obese subjects the following tests were carried out: placebo; dexamethasone alone (4 mg i.v. at 0 minutes); and dexamethasone plus pyridostigmine (120 mg p.o. at 60 minutes). In normal subjects we also studied the effects of hydrocortisone (100 mg i.v. at 0 minutes) and deflazacort (a corticosteroid that does not cross the blood-brain barrier) (60 mg i.v. at 0 minutes). In obese subjects we also assessed the effect of dexamethasone plus GHRH (100 micrograms i.v. at 150 minutes) on plasma GH levels. PATIENTS: Ten normal subjects and 22 obese subjects were studied. Normal controls were within 10% of their ideal body weight. Obese subjects had a body mass index of 37.1 +/- 1.1 (mean +/- SEM). MEASUREMENTS: Plasma GH levels were measured by radioimmunoassay. RESULTS: Dexamethasone-induced GH secretion in normal subjects (28.6 +/- 7.8 millimicron/l, P less than 0.05). Corticosteroids did not alter GH levels in obese subjects. Pretreatment with pyridostigmine increased dexamethasone-induced GH release in normal subjects (40.8 +/- 6.8 millimicron/l) but this did not achieve statistical significance. Dexamethasone plus pyridostigmine did not alter GH levels in obese subjects (8.0 +/- 1.6 mU/l). In some subjects, dexamethasone pretreatment potentiated GHRH-stimulated GH secretion, while in half the subjects the basal GH levels were not altered. In control subjects, hydrocortisone and deflazacort caused GH release similar to dexamethasone. CONCLUSIONS: Corticosteroids are a new and selective stimulus of GH secretion. They do not cause GH release in obese subjects. Their relative independence from cholinergic control suggest that they act by reducing somatostatin secretion.

Adrenal Cortex Hormones↗
PubMed1989

Characterization of yeast mitochondrial RNase P: an intact RNA subunit is not essential for activity in vitro.

We have previously described a mitochondrial activity that removes 5' leaders from yeast mitochondrial precursor tRNAs and suggested that it is a mitochondrial RNase P. Here we demonstrate that the cleavage reaction results in a 5' phosphate on the tRNA product and thus the activity is analogous to that of other RNase Ps. A mitochondrial gene called the tRNA synthesis locus encodes an A + U-rich RNA required for this activity in vivo. Two regions of this RNA display sequence similarity to conserved sequences in bacterial RNase P RNAs. This sequence similarity coupled with the analogous activities of the enzymes has led us to conclude that the RNAs are homologous and that the tRNA synthesis locus does code for the mitochondrial RNase P RNA subunit. The smallest and most abundant transcript of the tRNA synthesis locus is 490 nucleotides long. However, during purification of the holoenzyme, RNA is degraded and pieces of the original RNA are sufficient to support RNase P activity in vitro.

Bacillus subtilis↗
PubMed1988

Morbidity from bone harvest in major jaw reconstruction: a randomized trial comparing the lateral anterior and posterior approaches to the ilium.

A randomized prospective study was done to compare bone harvest morbidity in the lateral anterior versus the lateral posterior approach to the ilium. One hundred consecutive patients, requiring at least 60 ml of bone for continuity defects of the mandible, were randomly placed in equal groups in these two categories. Assessment of morbidity vectors included pain, ambulation, seroma, and blood loss. Results, in part, identified the posterior ilium harvest to have decreased morbidity in all variables. The reduced morbidity encountered, and the greater quantity of available bone, are both related to the anatomic differences between the anterior and posterior ilium. Accepted disadvantages were increased operating time and the need to turn the patient.

Adolescent↗
PubMed1987

Effects of pre- and postoperative irradiation on the healing of bone grafts in the rabbit.

Healing of cellular bone grafts irradiated at various times in the postsurgical course was compared to the healing characteristics of bone grafts placed into already irradiated tissue and to controls of irradiated host mandible in a rabbit model. Physical graft consolidation was assessed by load stress characteristics and serial histologic examination. Results indicated that grafts placed into already irradiated tissues failed to form bone in both phases of expected regeneration resulting in structurally weakened and histologically deficient ossicles. Bone grafts irradiated after placement were tolerant of irradiation. Bone grafts irradiated after four weeks were found to be less affected by irradiation than those irradiated within the first four weeks, forming an ossicle structurally and histologically superior to that of bone ossicles developed from grafts placed into irradiated tissues.

Animals↗
PubMed1986

Isolation and characterization of the TRM1 locus, a gene essential for the N2,N2-dimethylguanosine modification of both mitochondrial and cytoplasmic tRNA in Saccharomyces cerevisiae.

The trm1 mutation of Saccharomyces cerevisiae is a single nuclear mutation that affects a specific base modification of both cytoplasmic and mitochondrial tRNA. Transfer RNA isolated from trm1 cells lacks the modified base N2,N2-dimethylguanosine, and extracts from these cells do not have detectable N2,N2-dimethylguanosine-specific tRNA methyltransferase activity. As part of our efforts to determine how this mutation affects enzyme activities in two different cellular compartments we have isolated the TRM1 locus by genetic complementation. The TRM1 locus restores the N2,N2-dimethylguanosine modification to both cytoplasmic and mitochondrial tRNA in trm1 cells. An open reading frame in this TRM1 gene is essential for complementation of the trm1 phenotype. Expression of this open reading frame in Escherichia coli converts the organism from one that neither makes N2,N2-dimethylguanosine nor has N2,N2-dimethylguanosine-specific tRNA methyltransferase activity into one that does. This result suggests that the TRM1 locus is the structural gene for the tRNA modification enzyme and that both nuclear/cytoplasmic and mitochondrial forms of the methyltransferase are produced from the same gene.

Base Sequence↗
PubMed1986

Evaluation of monitoring antibodies to PGL-I in armadillos experimentally infected with M. leprae.

An enzyme-linked immunosorbent assay (ELISA) for IgM antibodies to the phenolic glycolipid-I antigen of Mycobacterium leprae was evaluated for efficacy in monitoring armadillos experimentally infected with the bacillus. IgM antibodies were detected in armadillos from 186 days after experimental infection until the animals were sacrificed. The ELISA demonstrated the establishment of infection earlier and more reliably than the histologic methods previously applied. Satisfactory yields of M. leprae from individual armadillos could be predicted 97% of the time, and the technique may be useful in identifying appropriate harvest times or resistance among armadillos. The ELISA seems to be a valuable adjunct for managing experimental infections of M. leprae in armadillos.

Animals↗
PubMed1981

Inhibition of de novo IgM antibody synthesis by thalidomide as a relevant mechanism of action in leprosy.

Thalidomide is well documented to be an effective treatment for erythema nodosum leprosum (ENL) occurring in lepromatous leprosy. To be beneficial, thalidomide must interfere with one or more of the several essential steps in the pathogenesis of this syndrome, which is presumed to be a clinical manifestation of an Arthur-type hypersensitivity. Since complexes of antigen and antibody would initiate these events, thalidomide could exert its most direct influence on reactants in this essential step. To determine whether thalidomide affected de novo antibody synthesis, the effect of the drug on the antibody response to sheep erythrocytes in mice was determined. Thalidomide significantly inhibited IgM antibody formation when fed to mice for 5 or 7 days before immunization with sheep erythrocytes. There was also a selective decrease in serum IgM concentrations among leprosy patients being treated with thalidomide for ENL. A clinically relevant site of action of thalidomide in ENL appears to be on the synthesis of IgM antibody. The target site of the drug among the macrophage, antibody-forming, and helper or suppressor lymphocytes remains to be elucidated.

Animals↗
PubMedDate not supplied

Lateralization of the inferior alveolar nerve with simultaneous implant placement: surgical techniques.

In the event of moderate to severe mandibular bone resorption posterior to the mental foramen, repositioning of the inferior alveolar nerve provides a greater amount of available bone for implant placement and reduces the risk of nerve injury. While neural paresthesia may initially occur, this altered sensation generally resolves spontaneously. Alveolar nerve repositioning may be possible in cases in which other procedures cannot be performed due to the extent of atrophy of the posterior mandibular alveolar crest. This article presents the surgical technique to achieve this objective.

Dental Implantation, Endosseous↗
PubMedDate not supplied

Activity of ascorbic acid in inhibiting the multiplication of M. leprae in the mouse foot pad.

Ascorbic acid was fed to mice in concentrations of 0.05%, 0.15%, and 0.45% w/w in the diet. Six months after inoculation of M. leprae into the foot pads, there were significantly fewer acid-fast bacilli harvested from animals receiving 0.15% and 0.45% w/w ascorbic acid than from control mice. On the other hand, M. leprae did multiply in mice fed ascorbic acid while no multiplication at all was observed in animals fed dapsone, clofazimine or rifampin. No toxic effects of ascorbic acid were noted in these mice.

Administration, Oral↗