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M Ortiz

Publications and source records attributed to M Ortiz.

At least 145 records · Page 8Linked to original sources
PubMed1986

Opentime heterogeneity during bursting of sodium channels in frog skeletal muscle.

Single voltage-activated Na+ channel currents were obtained from membrane patches on internally dialyzed skeletal muscle segments of adult frogs. The high channel density in these membranes permitted frequent observation of the "bursting mode" of individual Na+ channels during 400-ms records. We examined the opentimes within and between bursts on individual membrane patches. We used a new nonparametric statistical procedure to test for heterogeneity in the opentime distributions. We found that although 80% of all bursts consisted of opentimes drawn from a single distribution, the opentime distribution varied significantly from burst to burst. Significant heterogeneity was also detected within the remaining 20% of individual bursts. Our results indicate that the gating kinetics of individual Na+ channels are heterogeneous, and that they may occasionally change in a single channel.

Animals↗
PubMed1986

Two modes of gating during late Na+ channel currents in frog sartorius muscle.

Na+ currents were measured during 0.4-s depolarizing pulses using the cell-attached variation of the patch-clamp technique. Patches on Cs-dialyzed segments of sartorius muscle of Rana pipiens contained an estimated 25-500 Na+ channels. Three distinct types of current were observed after the pulse onset: a large initial surge of inward current that decayed within 10 ms (early currents), a steady "drizzle" of isolated, brief, inward unitary currents (background currents), and occasional "cloudbursts" of tens to hundreds of sequential unitary inward currents (bursts). Average late currents (background plus bursts) were 0.12% of peak early current amplitude at -20 mV. 85% of the late currents were carried by bursting channels. The unit current amplitude was the same for all three types of current, with a conductance of 10.5 pS and a reversal potential of +74 mV. The magnitudes of the three current components were correlated from patch to patch, and all were eliminated by slow inactivation. We conclude that all three components were due to Na+ channel activity. The mean open time of the background currents was approximately 0.25 ms, and the channels averaged 1.2 openings for each event. Neither the open time nor the number of openings of background currents was strongly sensitive to membrane potential. We estimated that background openings occurred at a rate of 0.25 Hz for each channel. Bursts occurred once each 2,000 pulses for each channel (assuming identical channels). The open time during bursts increased with depolarization to 1-2 ms at -20 mV, whereas the closed time decreased to less than 20 ms. The fractional open time during bursts was fitted with m infinity 3 using standard Na+ channel models. We conclude that background currents are caused by a return of normal Na+ channels from inactivation, while bursts are instances where the channel's inactivation gate spontaneously loses its function for prolonged periods.

Action Potentials↗
PubMed1986

Effect of luminal Na+ on the kinetics of intestinal absorption of sugars in vivo.

The effect of sodium concentration on the absorption kinetics of glucose, galactose and 3-o-methyl-glucose in rat and hamster jejunum in vivo has been studied. In consecutive 1 min periods the total absorption and absorption in presence of 0.5 mM phlorizin were measured. The difference between them was taken as the active transport rate. The perfusion rate value was 5.6 ml X min-1 and sugar concentrations in the perfusion solution ranged from 1 to 10 mM. The results for the different sodium concentrations show a nearly common Vmax for the same sugar and animal species, while the apparent KT values increase when the sodium concentration in the lumen decreases, mimicking a pure affinity-type activation system. The absorption of sugar when solutions without Na+ are perfused, is greater than that entering passively in the presence of phlorizin. An explanation may be that appreciable amounts of endogenous Na+ find their way to the intestinal lumen in favour of the gradient, making Na+-sugar cotransport possible.

Animals↗
PubMed1985

Slow currents through single sodium channels of the adult rat heart.

The currents through single Na+ channels from the sarcolemma of ventricular cells dissociated from adult rat hearts were studied using the patch-clamp technique. All patches had several Na+ channels; most had 5-10, while some had up to 50 channels. At 10 degrees C, the conductance of the channel was 9.8 pS. The mean current for sets of many identical pulses inactivated exponentially with a time constant of 1.7 +/- 0.6 ms at -40 mV. Careful examination of the mean currents revealed a small, slow component of inactivation at pulse potentials ranging from -60 to -30 mV. The time constant of the slow component was between 8 and 14 ms. The channels that caused the slow component had the same conductance and reversal potential as the fast Na+ currents and were blocked by tetrodotoxin. The slow currents appear to have been caused by repeated openings of one or more channels. The holding potential influenced the frequency with which such channel reopening occurred. The slow component was prominent during pulses from a holding potential of -100 mV, while it was very small during pulses from -140 mV. Ultraslow currents through the Na+ channel were observed occasionally in patches that had large numbers of channels. They consisted of bursts of 10 or more sequential openings of a single channel and lasted for up to 150 ms. We conclude that the single channel data cannot be explained by standard models, even those that have two inactivated states or two open states of the channel. Our results suggest that Na+ channels can function in several different "modes," each with a different inactivation rate.

Action Potentials↗
PubMed1984

Adverse drug reactions (ADRs) in patients with heart diseases. Comparison between patients without and with heart failure.

Adverse drug reactions (ADRs) may be more frequent in patients who present some diseases. By means of an intensive prospective drug surveillance work, 492 patients with heart diseases, hospitalized at the Department of Medicine of the Clinical Hospital of the University of Chile, were studied in order to determine the frequency and characteristics of ADRs. ADRs were significantly more frequent in patients with heart failure (HF) (30.0%) than in those without HF (22.7%)(p less than 0.05). Patients presenting HF developed more metabolic disturbances than patients not presenting HF (p less than 0.001). Furosemide was the most frequently used drug in both groups, but treatment with it was longer in patients with HF who presented a significantly higher frequency of adverse reactions to this diuretic (p less than 0.05). 89.9% of ADRs in patients without HF and 93.8% of ADRs in those with HF, were dose-related effects. Analyses of some predisposing factors to ADRs, such as age, number of drugs administered, duration of hospitalization, ADR or allergy histories and presence of a renal failure, did not explain differences found between ADRs in patients without and with HF. These findings suggest that heart failure may be a determinant of frequency and characteristics of ADRs.

Acetyldigitoxins↗
PubMed1983

There's no place like home.

Many children with chronic illness or handicapping conditions may not need continual or frequent institutional care, provided that suitable home care services are available. Yet, planning and experimentation with the concept of pediatric home care is just beginning on both the national and local levels and the concept of home care has yet to become widely understood and accepted. As a result, health planners and policy markers often fail to realize the potential advantage of home care to children, to families, and to society. Instead of seeing it as the most humane and effective way of caring for the chronically ill child, they see it as an increased financial burden. They also lack the perspective needed to realize that home care is ultimately the most cost-effective health care alternative, since it involves investing in people rather than in buildings or equipment. This report attempts to disseminate more widely the concept of home care by recounting a 2-year experience with a hospital-based pediatric home care service.

Child↗
PubMed1982

Influence of perfusion rate on the kinetics of intestinal sugar absorption in rats and hamsters in vivo.

The effect of perfusion rate (PR) on the apparent glucose and galactose-influx kinetics of rat and hamster jejunum in vivo has been studied. Total absorption (V) and absorption in the presence of 0.5 mM phloridzin (VD) were measured in consecutive periods of 1 minute, and their difference (VT = V - VD) was taken as the mediated transport rate. PR values were 2.8, 5,6, 13.5 or 18.5 ml.min-1, and the sugar concentrations in the perfusion solution (So) were 2, 5 and 10 mM. Plots of 1/VT versus 1/So for the different PR intercept the ordinate axis at the same point, yielding a common Vmax for the same animal species and sugar. From the slopes, apparent K'm values are obtained and apparent mass-transfer coefficients (K'D) for the diffusion component are calculated (VD/So) as well. When the PR increases, K'n decreases, while K'D increases. A simplified model based on the assumption of a steady-state in which diffusion across unstirred water layers (UWL) equals the sum of a passive and a carrier mediated non-passive transepithelial transfer, acceptably accounts for the results. When taking a "true" Km values the lowest ones reported in the literature, it is possible to obtain the sugar concentration at the enterocyte membrane (Sm), the effective UWL thickness (delta) and the "true" mass-transfer coefficient (KD). So/Sm ratios and delta values decrease as PR increases, accounting for the biased K'm and K'D values. As it was expected, KD did not change significantly by modifying PR. Depending on sugar concentration, the passive component is almost equal to or much higher than the carrier-mediated transport, in rat as well as in hamster. Diffusion across unstirred water layers seems to be rate-limiting for intestinal sugar absorption.

Animals↗
PubMed1982

Influence of temperature of the perfusion solution on the kinetics of intestinal absorption of glucose in rats.

The kinetics of glucose intestinal absorption by rat jejunum at different solution temperatures, under single pass perfusion, has been studied in vivo. The non-passive component (active transport) has been measured as difference between control absorption and that in the presence of 5 X 10(-4) M phloridzin. Results at 37 degrees and 39 degrees C did not significantly differ, but at 32 degrees C a clear drop in total absorption, non-passive and passive components was observed. As temperature increases from 32 degrees to 37 degrees C the apparent value of Km for glucose transport decreases (from 21.2 mM to 13.1 mM), whilst the Vmax does not change, and the apparent mass-transfer coefficient for the passive component slightly increases. The results are discussed taking in consideration the effect of temperature on the diffusion across the unstirred water layers and on the active transport processes.

Animals↗
PubMed1982

Competitive kinetics in the inhibition of sugar intestinal transport by phlorizin, in vivo.

Kinetics of sugar transport inhibition by phlorizin in rat intestine has been studied in vivo. Jejunum lumen was perfused during a series of successive 1 minute periods of absorption. Total sugar absorption was assumed to be the sum of a mediated transport component plus a passive one persisting in the presence of 5 X 10(-4) M phlorizin. The values of transport rates, corrected in this way, showed Michaelis-Menten kinetics and proved that inhibition of D-glucose, D-galactose and 6-deoxy-D-glucose transport by low concentrations of phlorizin (5 X 10(-6) M) displays a typical competitive kinetics (apparent Ki = 4-10 X 10(-6) M) as had been long before reported from in vitro experiments.

Animals↗
PubMed1979

Effect of the pH on intestinal absorption of sugars in vivo.

Influence of the pH on the absorption rate of sugars by rat intestine in vivo has been revised by means of a technique for intestinal lumen perfusion with 1 minute absorption periods. Absorption at pH 2.5, 5, 7, 8.5, and 10 has been comparied in each animal. Absorption rate of D-glucose, D-galactose and D-fructose is highest at pH 7 and decreases at the lower or higher pH values. The pH does not affect the absorption of D-arabinose. The pH effect is attributed to changes in the transport system for sugars.

Animals↗
PubMed1979

Influence of luminal Na+ on the intestinal absorption of sugars in vivo.

The effect of substituting Na+ with Tris, Li+, K+ or mannitol on the intestinal absorption of sugars, in successive periods of 1 minute duration, has been studied in rat and hamster in vivo. The absorption of 2 mM D-glucose, D-galactose, 3-0-methyl-D-glucose and D-fructose is clearly inhibited in the absence of Na+, up to 70-80%, and returns to its normal value of restoring Na+. The degree of inhibition varies with the sugar, increases on lowering Na+ concentration, reaches maximum values with mannitol as substituent, and minimum with Tris, D-arabinose absorption is not affected by Na+. These results prove once more how important Na+ is in sugar intestinal transport in vivo, while they reveal additional influences of the different substituents on the transport system.

Animals↗
PubMed1976

Osseous autografts. III. Comparison of osseous coagulum-bone blend implants with open curetage.

A clinical investigation was undertaken to compare regeneration of osseous defects following either osseous coagulum-bone blend grafts or open debridement procedures. Seventy-five sites in 28 patients were treated by the two procedures. The average fill in the 37 intraosseous defects treated by graft procedures (initial average depth = 4.22 mm, S.D. 1.73) was 2.98 mm, S.D. 1.44. The average fill in the 38 intraosseous lesions treated by open debridement procedure (initial average depth = 3.03 mm, S.D.0.80) was 0.66 mm, S.D. 0.80. Statistical analysis showed a significant difference (P greater than 0.01) in fill patterns between the bone blend and open debridement responses in favor of graft treated sites. Therefore greater levels of osseous regeneration apparently took place in our cases following osseous coagulum-bone blend autogenous graft procedures than following open debridement procedures in all types of defects studies.

Adult↗
PubMedDate not supplied

Depersonalization in panic disorder: a clinical study.

Panic disorder (PD) has been hypothesized to be a heterogeneous entity, with distinct clinical subgroups. The presence of depersonalization during panic attacks may distinguish a specific subgroup of PD. We sought to analyze the differential features of a subgroup of PD patients with depersonalization. A total of 274 patients with PD were assessed and divided into 2 groups according to the presence or absence of depersonalization. The Structured Clinical Interview for DSM-III-R (SCID-UP-R) was used to assess PD and comorbid disorders. The clinical scales administered included the Hamilton Anxiety and Depression Rating Scale (HARS and HDRS), the Marks and Mathews Fears and Phobia Scale, Panic-Associated Symptom Scale (PASS), and a panic attack symptoms inventory. A total of 66 patients (24.1%) exhibited depersonalization during the attacks. Patients with depersonalization appeared to be younger and had an earlier age at onset. PD was more severe in the depersonalization group (greater number of attacks, worse level of functioning, and higher scores on most self-rating scales). Also, depersonalization patients showed more comorbidity with specific phobia. Our results support the view that PD with depersonalization may be considered a distinct and more severe subcategory of PD.

Adolescent↗