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J Ibarra

Publications and source records attributed to J Ibarra.

At least 37 records · Page 2Linked to original sources
PubMed1991

Dynamics of the inward rectifier K+ current during the action potential of guinea pig ventricular myocytes.

The potassium selective, inward rectifier current (IK1) is known to be responsible for maintaining the resting membrane potential of quiescent ventricular myocytes. However, the contribution of this current to the different phases of the cardiac action potential has not been adequately established. In the present study, we have used the action potential clamp (APC) technique to characterize the dynamic changes of a cesium-sensitive (i.e., Ik1) current which occur during the action potential. Our results show that (a) Ik1 is present during depolarization, as well as in the final phase of repolarization of the cardiac action potential. (b) The current reaches the zone of inward-going rectification before the regenerative action potential ensues. (c) The maximal outward current amplitude during repolarization is significantly lower than during depolarization, which supports the hypothesis that in adult guinea pig ventricular myocytes, Ik1 rectification is accentuated during the action potential plateau. Our results stress the importance of Ik1 in the modulation of cell excitability in the ventricular myocyte.

Action Potentials↗
PubMed1991

Dynamics of the background outward current of single guinea pig ventricular myocytes. Ionic mechanisms of hysteresis in cardiac cells.

Subthreshold potentials are thought to be mediated by time-independent, "passive" background currents. In this study, we show that the background current-voltage (I-V) relation of guinea pig ventricular myocytes is changed significantly by repetitive stimulation, in such a way that cell excitability becomes enhanced. Myocytes were used for whole-cell voltage-clamp experiments. A voltage-clamp ramp (100 mV/sec) to -50 mV was applied from a holding potential of -100 mV. Subsequently, a train of square voltage-clamp pulses to +10 mV (duration, 300 msec; interpulse interval, 300 msec) was delivered from a holding potential of -85 mV. A new ramp was applied again immediately after the train, and the resulting I-V curve was compared with that obtained before the train. Pulsing displaced the I-V relation to the right, the zero-current point becoming 1-2 mV less negative, and increased the degree of inward-going rectification. These changes were insensitive to tetrodotoxin (30 microM); disappeared during superfusion with cobalt (2 mM), verapamil (22 microM), or ryanodine (5 microM); and could not be mimicked by agonists of the protein kinase C system. In the presence of cesium (8 mM), pulsing still displaced the I-V curve to the right. However, the linear portion of the curve became steeper after the train. Subtraction of the cesium-sensitive current from control revealed that, although the zero-current point remained constant, the I-V relation showed a stronger inward-going rectification after pulsing. In accordance with these results, we have demonstrated hysteresis of excitability in ventricular myocytes. We conclude that the observed changes are mediated by an increase in intracellular calcium, which leads to an increase in rectification of IK1, as well as to activation of another membrane-conductance system, perhaps the Na-Ca exchange or the Ca(2+)-activated, nonselective current.

Animals↗
PubMed1986

Sonographic demonstration of simultaneous intrauterine and extrauterine gestation.

Simultaneous intrauterine and ectopic pregnancies are extremely rare. The diagnosis is usually made by laparoscopy and/or laparotomy. Three cases are presented in which the diagnosis was made during sonographic examinations by simultaneous demonstration of fetal cardiac motion in both the intrauterine and extrauterine fetuses. Early diagnosis of this condition significantly reduces the morbidity and mortality of both the mother and the intrauterine gestation.

Adult↗
PubMed1984

Reflex regional vascular responses during passive gastric distension in cats.

The increase in systemic vascular resistance during gastric distension in cats may result from variable vasomotor responses in several parallel regional vascular beds. Accordingly, in 23 anesthetized cats the stomach was passively distended with a balloon while systemic hemo-dynamics were monitored. Regional vascular responses were determined during control periods and during gastric distension either by injection of radioactive microspheres (15 cats) or by constant perfusion of vascularly isolated organs (8 cats). During distension, mean arterial pressure and systemic vascular resistance increased by 32 and 28%, respectively. Regional flow measurements indicated no significant alterations in any of the organs examined. Calculated regional vascular resistances indicated vasoconstriction in the kidneys (53%), small intestine (31%), and large intestine (37%) that was reversed by alpha-adrenergic blockade with phentolamine. Constant-flow perfusion studies confirmed the regional vasoconstriction in the renal, superior mesenteric, and hindlimb circulations. These studies suggest a regional heterogeneity of vasomotor response during passive gastric distension in cats that includes no change in vascular resistance in some organs and alpha-adrenergic vasoconstriction in others.

Adrenergic alpha-Antagonists↗
PubMed1982

Sympathoadrenal mechanisms in hemodynamic responses to gastric distension in cats.

There is presently little information on the efferent mechanisms responsible for the reflex cardiovascular activation during passive gastric distension. Therefore, 40 cats anesthetized with alpha-chloralose were studied with passive gastric balloon distention before and during 1) two repeated gastric distensions, 2) beta-adrenergic blockade with propranolol, 3) alpha-adrenergic blockade with phentolamine, or 4) bilateral adrenalectomy. Before and during each distension mean arterial pressure, heart rate, cardiac output, rate of rise of left ventricular pressure (dP/dt) at 40 mmHg developed pressure and calculated systemic vascular resistance were determined. Repeated gastric distension caused similar hemodynamic responses without tachyphylaxis. beta-Blockade significantly reduced the increase in dP/dt from 893 +/- 362 to 150 +/- 63 mmHg/s. alpha-Blockade significantly altered the changes in mean arterial pressure from 33 +/- 5.0 to -2 +/- 4.7 mmHg and systemic vascular resistance from 0.114 +/- 0.019 to 0.004 +/- 0.031 peripheral resistance units. Bilateral adrenalectomy significantly diminished the contractile response from 525 +/- 107 to 50 +/- 85 mmHg/s but did not significantly alter the pressor and vasoconstrictor responses. We conclude that, during passive gastric distension in cats, the increase in myocardial contractility is mediated by beta-adrenergic-receptor stimulation, whereas the arterial vasoconstrictor and pressor responses are mediated by alpha-adrenergic receptor stimulation. Additionally, during gastric distension a substantial portion of the contractile response is dependent on the integrity of the adrenal glands.

Adrenalectomy↗
PubMedDate not supplied

Electrophysiological and behavioral methods in early detection of hearing impairment.

BACKGROUND: Recent advances in neonatal life-support systems have contributed to the survival of high-risk newborns. However, protection of the auditory system and the prevention of sequelae is still paramount in neonatal neurology. The aim of this study was to compare auditory-evoked responses with a toy test and acoustic reflex in the early detection of hearing loss in infants. METHODS: Three groups were studied. The first was composed of infants showing less than a 30 dB biaural threshold in the neurophysiological test. The second group was made up of infants showing peripheral alterations on one side or both ears. The third group was comprised of infants who showed no responses at 95 dB HL in both ears after neurophysiological testing. The neurophysiological test, toy test, and acoustic reflex were performed on the same day, with masked results given to each investigator. Sensitivity and specificity for each toy test and acoustic reflex were calculated afterward. RESULTS: Forty-five controls, 44 peripheral alterations, and 8 non-response infants were studied. Most patients studied were born prior to the 37(th) week of gestation with a birthweight of less than 2,250 g, received required administration of potential ototoxic drugs and mechanical ventilation, and showed hyperbilirubinemia and hypoxia. Sensitivity for each toy was as follows: drum 0.54; wooden rattle 1.0, and metallic ratle 0.88. Specificity was 0.95, 1.0, and 1.0, respectively. Acoustic reflex sensitivity was 0.38 and specificity was 0.97. CONCLUSIONS: Results suggest that the wooden and the metallic rattles of the toy test can be useful tools in the study of hearing in the high-risk infant and deserve more attention in future studies.

Deafness↗
PubMedDate not supplied

[Dry powdered formoterol, twice a day versus aerosolized salbutamol, four times a day, in patients with stable asthma].

MATERIAL AND METHODS: The objective of this multicenter, open randomized study was to compare the effect of inhaled formoterol (dry powder with ISF system) 12 mcg twice daily versus salbutamol (200 mg qid) in patients with bronchial asthma. A total of 160 patients were evaluated with such diagnosis in four specialized centers; the main variable was the maximal respiratory flow (MEF) assessed prior to drug administration (morning and afternoon). In addition to this, vital capacity (VC), forced respiratory volume over one second (FEV-1), and other safety variables were also determined. RESULTS: With regard to MEF the administration of formoterol showed better results (P < 0.05) ever since the first month of treatment. The frequency of adverse events was similar between treatment groups; the formoterol group had fewer nightly wake up periods. CONCLUSIONS: That formoterol is a safe, efficacious and long-acting Beta 2 agonist which can be administered twice daily.

Adolescent↗