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Biomedical subjects

G Gambassi

Publications and source records attributed to G Gambassi.

At least 73 records · Page 4Linked to original sources
PubMed1995

Mitochondrial membrane potential in single living adult rat cardiac myocytes exposed to anoxia or metabolic inhibition.

1. The relation between mitochondrial membrane potential (delta psi m) and cell function was investigated in single adult rat cardiac myocytes during anoxia and reoxygenation. delta psi m was studied by loading myocytes with JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'- tetra-ethylbenzimidazolylcarbocyanine iodide), a fluorescent probe characterized by two emission peaks (539 and 597 nm with excitation at 490 nm) corresponding to monomer and aggregate forms of the dye. 2. De-energizing conditions applied to mitochondria, cell suspensions or single cells decreased the aggregate emission and increased the monomer emission. This latter result cannot be explained by changes of JC-1 concentration in the aqueous mitochondrial matrix phase indicating that hydrophobic interaction of the probe with membranes has to be taken into account to explain JC-1 fluorescence properties in isolated mitochondria or intact cells. 3. A different sensitivity of the two JC-1 forms to delta psi m changes was shown in isolated mitochondria by the effects of ADP and FCCP and the calibration with K+ diffusion potentials. The monomer emission was responsive to values of delta psi m below 140 mV, which hardly modified the aggregate emission. Thus JC-1 represents a unique double sensor which can provide semi-quantitative information in both low and high potential ranges. 4. At the onset of glucose-free anoxia the epifluorescence of individual myocytes studied in the single excitation (490 nm)-double emission (530 and 590 nm) mode showed a gradual decline of the aggregate emission, which reached a plateau while electrically stimulated (0.2 Hz) contraction was still retained. The subsequent failure of contraction was followed by the rise of the emission at 530 nm, corresponding to the monomer form of the dye, concomitantly with the development of rigor contracture. 5. The onset of the rigor was preceded by the increase in intracellular Mg2+ concentration ([Mg2+]i) monitored by mag-indo-1 epifluorescence. Since under these experimental conditions intracellular [Ca2+] and pH are fairly stable, the increase in [Mg2+]i was likely to be produced by a decrease in ATP content. 6. The inhibition of mitochondrial ATPase induced by oligomycin during anoxia was associated with a rapid and simultaneous change of both the components of JC-1 fluorescence, suggesting that delta psi m, instead of producing ATP, is generated by glycolytic ATP during anoxia. 7. The readmission of oxygen induced a rapid decrease of the monomer emission and a slower increase of the aggregate emission. These fluorescence changes were not necessarily associated with the recovery of mechanical function.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Diphosphate↗
PubMed1995

Association of serum creatinine and age with headache caused by nitrates. Gruppo Italiano di Farmacovigilanza nell'Anziano.

To assess whether serum creatinine and age are associated with headache induced by nitrates, 2742 hospitalized patients taking nitrates were studied during their hospital stay. Those patients with admission serum creatinine levels from 97 to 133 mumol/L and > 133 mumol/L were compared with patients with creatinine levels < 97 mumol/L. Gender, body mass index, comorbidity, cognitive status, new intake of nitrates, number of daily administrations, and daily dosage, as well as intake of angiotensin converting enzyme inhibitors, calcium antagonists, diuretics and nonsteroidal anti-inflammatory drugs were examined as possible confounders. Fifty-six patients had headaches that had a causal link with intake of nitrates. Compared with the lowest creatinine group, after adjustment for potential confounding variables, the odds ratios and 95% confidence interval (95% CI) for headache caused by nitrates associated with increasing serum creatinine levels were 0.6 (95% CI, 0.3 to 1.1) and 0.2 (95% CI, 0.0 to 1.2), respectively (p for trend = 0.013). Increasing age was inversely associated with headache (odds ratio for 10-year increase, 0.6 [95% CI, 0.5 to 0.7]). Serum creatinine and age were independently and inversely associated with headache caused by nitrates.

Aged↗
PubMed1994

Temperature modulates calcium homeostasis and ventricular arrhythmias in myocardial preparations.

OBJECTIVE: The aim was to evaluate the effect of temperature on reoxygenation induced ventricular arrhythmias in isolated hearts, on delayed afterdepolarisations and Iti current in Purkinje fibres, and on sarcoplasmic reticular function and Ca2+ handling of single cardiac myocytes. METHODS: Isolated guinea pig hearts were retrogradely perfused at 37 degrees C with a hypoxic medium for 15 min and reoxygenated for 10 min either at 33 degrees C or at 37 degrees C. Intracellular microelectrodes were used to assess the presence of delayed afterdepolarisations and triggered activity in sheep Purkinje fibres exposed to strophanthidin at different temperatures. Iti current was evaluated in voltage clamp experiments. In rat cardiomyocytes, loaded with the fluorescent Ca2+ dye, indo-1, the sarcoplasmic reticular Ca2+ content was assessed at 30 degrees C and at 37 degrees C, either by a caffeine spritz puffed onto a cell from a patch pipette or by a post-rest contraction. RESULTS: Hypothermic reoxygenation reduced the incidence of ventricular arrhythmias in isolated hearts (30%, n = 10, at 33 degrees C and 75%, n = 30, at 37 degrees C, p < 0.05). In Purkinje fibres, hypothermia decreased the amplitude of delayed afterdepolarisations. Moreover, at 32 degrees C, the amplitude of Iti current was decreased to 59.2(SEM 2.6)% of the normothermic value [27.5(6.7) nA, n = 4, p < 0.005] and time to peak increased to 159.7(10.2)% [value at 37 degrees C = 470(41) ms, n = 4, p < 0.01]. In cardiac cells, sarcoplasmic reticular Ca2+ release induced by caffeine spritz or by post-rest contraction was increased at 30 degrees C. However, following a pacing period at 1 Hz, hypothermia prolonged the time to onset of the first spontaneous Ca2+ oscillation [59(14) s at 30 degrees C and 27(9) s at 37 degrees C, n = 5, p < 0.05] and reduced the oscillation frequency [1.1(0.4) min-1 at 30 degrees C and 3.1(0.9) min-1 at 37 degrees C, n = 5, p < 0.05]. CONCLUSIONS: Mild hypothermia increases sarcoplasmic reticular Ca2+ content but decreases the likelihood of spontaneous Ca2+ release. This may explain the reduction of delayed afterdepolarisations and Iti current amplitude in Purkinje fibres and it could represent a mechanism for the protection provided by hypothermia against ventricular arrhythmias.

Action Potentials↗
PubMed1994

Postsurgical complications in older patients. The role of pharmacological intervention.

The number of elderly patients undergoing surgery has been rapidly increasing during the last few years. Following surgical interventions, high rates of mortality and morbidity have been reported in the most advanced age groups. Nevertheless, perioperative evaluation and postoperative care are the major determinants of the overall outcome. Postsurgical complications are common in advanced age, since multiple pathology is often present in geriatric patients. Furthermore, the decreased efficiency of homeostatic mechanisms may facilitate the development of multiple organ failure (MOF), even as a consequence of apparently slight alterations in immune, cardiac or respiratory systems. Thus, prompt recognition and treatment of any complication often prevents the development of irreversible conditions. While cardiac and pulmonary complications account for 50% of early postoperative adverse events, infections, thromboembolism, renal failure, stress ulcers and coagulation disorders may occur well after surgical procedures. An important part of postoperative geriatric care is the diagnosis and correction of fluid, electrolyte and acid-base disturbances. These disturbances may manifest as mild, atypical signs, such as slight neuromuscular depression or delirium. Yet, they often constitute life-threatening conditions that should be rapidly and properly corrected. Finally, it should be remembered that, due to the frequent use of multiple drugs, elderly patients are at high risk of developing adverse drug reactions. Thus, the treatment of postoperative complications requires a strong rational effort to disentangle the combined effects of aging, drugs and pathology.

Analgesics↗
PubMed1993

The impact of age on risk of adverse drug reactions to digoxin. For The Gruppo Italiano di Farmacovigilanza nell' Anziano.

To assess the association of age and other potential risk factors with digoxin toxicity, adverse drug reactions to digoxin (ADRDIG) were studied in all patients (n = 1338) on digoxin therapy consecutively admitted to 41 clinical wards throughout Italy during 4 months in 1988. At the time of admission, 28 patients (2.1%) had evidence of ADRDIG. In multivariate logistic regression analysis, significant associations with ADRDIG were found for age > or = 80 years compared to age 65-79 years (OR = 2.75, 95% CI = 1.17-6.45), daily digoxin dosage of > or = 0.25 mg (OR = 2.51, 95% CI = 1.16-5.47), serum creatinine > or = 120 mumol/L (OR = 3.75, 95% CI = 1.69-8.32), and for treatment with amiodarone, propafenone, quinidine or verapamil (OR = 2.60, 95% CI = 1.07-6.30). Those aged < 65 years had a similar risk of digoxin toxicity as those aged 65-79 years (OR = 1.07, 95% CI = 0.28-4.12). Adverse drug reactions to digoxin were found in 1 in 50 patients hospitalized on digoxin therapy. Patients aged 65-79 years were not at increased risk for digoxin toxicity compared to younger patients, while advanced age (> or = 80 years) was an independent risk factor for this outcome.

Adolescent↗
PubMed1993

Effects of acidosis on resting cytosolic and mitochondrial Ca2+ in mammalian myocardium.

Acidosis increases resting cytosolic [Ca2+], (Cai) of myocardial preparations; however, neither the Ca2+ sources for the increase in Cai nor the effect of acidosis on mitochondrial free [Ca2+], (Cam) have been characterized. In this study cytosolic pH (pHi) was monitored in adult rat left ventricular myocytes loaded with the acetoxymethyl ester (AM form) of SNARF-1. A stable decrease in the pHi of 0.52 +/- 0.05 U (n = 16) was obtained by switching from a bicarbonate buffer equilibrated with 5% CO2 to a buffer equilibrated with 20% CO2. Electrical stimulation at either 0.5 or 1.5 Hz had no effect on pHi in 5% CO2, nor did it affect the magnitude of pHi decrease in response to hypercarbic acidosis. Cai was measured in myocytes loaded with indo-1/free acid and Cam was monitored in cells loaded with indo-1/AM after quenching cytosolic indo-1 fluorescence with MnCl2. In quiescent intact myocytes bathed in 1.5 mM [Ca2+], hypercarbia increased Cai from 130 +/- 5 to 221 +/- 13 nM. However, when acidosis was effected in electrically stimulated myocytes, diastolic Cai increased more than resting Cai in quiescent myocytes, and during pacing at 1.5 Hz diastolic Cai was higher (285 +/- 17 nM) than at 0.5 Hz (245 +/- 18 nM; P < 0.05). The magnitude of Cai increase in quiescent myocytes was not affected either by sarcoplasmic reticulum (SR) Ca2+ depletion with ryanodine or by SR Ca2+ depletion and concomitant superfusion with a Ca(2+)-free buffer. In unstimulated intact myocytes hypercarbia increased Cam from 95 +/- 12 to 147 +/- 19 nM and this response was not modified either by ryanodine and a Ca(2+)-free buffer or by 50 microM ruthenium red in order to block the mitochondrial uniporter. In mitochondrial suspensions loaded either with BCECF/AM or indo-1/AM, acidosis produced by lactic acid addition decreased both intra- and extramitochondrial pH and increased Cam. Studies of mitochondrial suspensions bathed in indo-1/free acid-containing solution showed an increase in extramitochondrial Ca2+ after the addition of lactic acid. Thus, in quiescent myocytes, cytoplasmic and intramitochondrial buffers, rather than transsarcolemmal Ca2+ influx or SR Ca2+ release, are the likely Ca2+ sources for the increase in Cai and Cam, respectively; additionally, Ca2+ efflux from the mitochondria may contribute to the raise in Cai. In contrast, in response to acidosis, diastolic Cai in electrically stimulated myocytes increases more than resting Cai in quiescent cells; this suggests that during pacing, net cell Ca2+ gain contributes to enhance diastolic Cai.

Acidosis↗
PubMed1993

Intramitochondrial free calcium in cardiac myocytes in relation to dehydrogenase activation.

OBJECTIVE: The aim was to quantitate intramitochondrial free Ca2+ ([Ca2+]m) in cardiac myocytes under conditions of stimulation previously shown to cause activation of pyruvate dehydrogenase. METHODS: [Ca2+]m was monitored in single, isolated rat cardiac myocytes using fluorescence microscopy following the loading of the cells with the fluorescent chelating agent indo-1, in its permeant acetoxymethylester form, and the selective quenching of cytosolic fluorescence with MnCl2. The extent of contraction upon electrical stimulation was also measured. RESULTS: Electrical stimulation at 2 Hz and higher frequency raised [Ca2+]m significantly, and this was potentiated by exposure to isoprenaline. However, isoprenaline had no effect in quiescent cells, in which [Ca2+]m was raised above resting values by partial replacement of Na+ in the medium. The mitochondrial uncoupling agent carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) raised [Ca2+]m in unstimulated cells, but lowered it in cells subjected to electrical stimulation at 2 Hz or more, to partial Na+ replacement, or to the alkaloid veratridine. CONCLUSIONS: The values of [Ca2+]m in quiescent myocytes (approximately 100 nmol.litre-1) would be associated with very little activation by Ca2+ of pyruvate dehydrogenase phosphatase, based on determination of K0.5 value of 650 nmol.litre-1 in work with mitochondrial suspensions. By contrast, the values of [Ca2+]m associated with electrical stimulation at 2 Hz or greater in the presence of beta adrenergic activation (> 500 nmol.litre-1) would be associated with significant dehydrogenase activation. The effect of beta adrenergic activation is only seen in the presence of electrical stimulation and probably involves enhancement of systolic transients in cytosol [Ca2+]. Effects of uncoupling agents validate the conclusions on the direction and magnitude of the mitochondrial Ca2+ gradient in situ in living myocytes.

Animals↗