Papers by Sergio Visentin
Lacidipine is a new 1,4-dihydropyridine derivative with potent and long-lasting antihypertensive ... more Lacidipine is a new 1,4-dihydropyridine derivative with potent and long-lasting antihypertensive activity. We used intracellular microelectrodes to characterize the electrophysiologic properties of lacidipine on different cardiac preparations. Lacidipine (10(-8) -10(-6) M) dose-dependently decreased contractility of driven sheep Purkinje fibers. For concentrations less than or equal to 10(-7) M, this effect was associated with a selective decrease of the plateau height. Higher concentrations (3 X 10(-7) and 10(-6) M), however, affected action potential amplitude, overshoot, and maximum rate of depolarization. In the same range of concentrations, lacidipine did not affect normal automaticity of guinea-pig sinus node and sheep Purkinje fibers. Lacidipine (10(-6) M) consistently blocked barium-induced abnormal automaticity in Purkinje fibers and reduced the amplitude and Vmax of the slow action potentials induced by histamine (10(-5) M) in guinea pig papillary muscle depolarized by potassium (22 mM). The effect of lacidipine on the slow inward current (Isi) was studied in shortened Purkinje fibers under voltage-clamp conditions. Lacidipine (10(-7)-10(-6) M) reduced the Isi without affecting the I-V relationship. None of the effects of lacidipine was reversed by 2-h washout. The results indicate that lacidipine has calcium-antagonistic properties in cardiac tissues. Its cardiac effects occur at concentrations 100 times higher than those active in the vascular smooth muscle. The lack of recovery of the lacidipine effects suggests that its interaction with the calcium channel may occur at an inner site of the cell membrane.
Cells
Astrocytes, the most numerous cells of the central nervous system, exert critical functions for b... more Astrocytes, the most numerous cells of the central nervous system, exert critical functions for brain homeostasis. To this purpose, astrocytes generate a highly interconnected intercellular network allowing rapid exchange of ions and metabolites through gap junctions, adjoined channels composed of hexamers of connexin (Cx) proteins, mainly Cx43. Functional alterations of Cxs and gap junctions have been observed in several neuroinflammatory/neurodegenerative diseases. In the rare leukodystrophy megalencephalic leukoencephalopathy with subcortical cysts (MLC), astrocytes show defective control of ion/fluid exchanges causing brain edema, fluid cysts, and astrocyte/myelin vacuolation. MLC is caused by mutations in MLC1, an astrocyte-specific protein of elusive function, and in GlialCAM, a MLC1 chaperon. Both proteins are highly expressed at perivascular astrocyte end-feet and astrocyte-astrocyte contacts where they interact with zonula occludens-1 (ZO-1) and Cx43 junctional proteins. To...
Proceedings of the Royal Society B: Biological Sciences, 1985
The fast transient inward current elicited by depolarizations above about -60 mV in calf Purkinje... more The fast transient inward current elicited by depolarizations above about -60 mV in calf Purkinje fibres was found to be depressed by Cd in concentrations less than 1 mM. The Cd-sensitive current, which strongly depended on external Na, was recorded in the presence of 2 mM MnCl2 and was blocked by TTX, indicating that a contamination from slow Ca-dependent currents could be discounted. The current reduction caused by Cd was also observed in nominally Ca-free solutions. The Cd-induced depression of the fast Na current was not accompanied by changes in the current kinetic parameters, as revealed by comparing inactivation curves and peak current voltage relations at different Cd concentrations, and could be attributed to a voltage-independent channel blocking action. Half-blockade occurred at 0.182 +/- 0.06 mM (n = 4). Plots of peak current amplitude as a function of the Cd concentration showed that the cooperation of two Cd ions was required to block a single channel.
Pfl�gers Archiv European Journal of Physiology, 1990
The action of group IIb cations [Cadmium (Cd2+), Zinc (Zn2+), Mercury (Hg2+)] on the cardiac fast... more The action of group IIb cations [Cadmium (Cd2+), Zinc (Zn2+), Mercury (Hg2+)] on the cardiac fast sodium current (INa) was investigated in calf Purkinje fibres and in ventricular cells isolated from guinea-pig hearts. In calf Purkinje fibres, INa was depressed by submillimolar concentrations of Zn2+ and Hg2+. With both cations, the current reduction occurred at all voltages in the range of current activation and the voltage dependence of peak current was unchanged. The degree of peak current inhibition depended on the cation concentration but not on voltage. The position of the inactivation curve on the voltage axis was unaltered at cation concentrations giving substantial current inhibition, and moved to the right only with concentration exceeding 1-1.5 mM. These effects can be interpreted as due to INa channel blockade. The action of Zn2+ and Hg2+ was similar to that described earlier of Cd2+ on Purkinje fibres (DiFrancesco et al. 1985b). INa was also inhibited by group IIb cations in isolated guinea-pig ventricular cells. Depression of INa by Cd2+, Zn2+ and Hg2+ was essentially voltage-independent, in agreement with its being caused by channel block. The dependence of INa block by Cd2+ upon external Na concentration [Na+0] was investigated in ventricular myocytes. The fraction of INa block by 0.1 mM CdCl2 was 0.50 at 140 mM, 0.81 at 70 mM and 0.83 at 35 mM [Na+]0. A similar increase of block efficiency at low [Na+0] was observed with 0.05 mM CdCl2. In both the Purkinje fibre and the ventricular cell, the order of potency of INa block by group IIb cations was Hg2+ greater than Zn2+ greater than Cd2+. Manganese (Mn2+, 2-5 mM), an ion of group VIIa, also depressed the INa in Purkinje fibres and ventricular myocytes. This effect was however due mainly to a positive shift on the voltage dependence of current kinetics rather than to a reduction of the conductance of the channel (GNa), and can be accounted for by an ion-screening action of Mn2+ on the external membrane surface. The block by group IIb cations is a typical property of cardiac Na+ channels and characterizes the cardiac as opposed to other types of Na+ channel.
Cardiovasc Drug Therapy, 1987
We studied the electrophysiological effects of the specific [32-agonist tulobuterol in the guinea... more We studied the electrophysiological effects of the specific [32-agonist tulobuterol in the guinea-pig sinus node and in sheep cardiac Purkinje fibers. Stimulation of 132-adrenoce ptots by tulobuterol resulted in a slight increase in the rate of firing of the sinus node. In Purkinje fibers, however, automaticity was not affected up to eoncentratmns of 10 M. Consistently, -g -{ . tulobuterol (10 -10 M) d d not affect the pacemaker current studied under voltage-clamp conditions. In the same range of concentrations (I0 -a-i0 -~ M) tulobuterol dose-dependently increased the contractile force of driven Purkinje fibers. Tulobuterol, at a very high concentration (10 -5 M), had membrane depressant effects as demonstrated by the block of automaticity induced in the spontaneously beating Purkinje fibers and by the reduction of the maximum rate of depolarization in driven preparations.
Cardiologia (Rome, Italy)
Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, 2015
Xeroderma pigmentosum (XP)-A patients are characterized by increased solar skin carcinogenesis an... more Xeroderma pigmentosum (XP)-A patients are characterized by increased solar skin carcinogenesis and present also neurodegeneration. XPA deficiency is associated with defective nucleotide excision repair (NER) and increased basal levels of oxidatively induced DNA damage. In this study we search for the origin of increased levels of oxidatively generated DNA lesions in XP-A cell genome and then address the question of whether increased oxidative stress might drive genetic instability. We show that XP-A human primary fibroblasts present increased levels and different types of intracellular reactive oxygen species (ROS) as compared to normal fibroblasts, with O2- and H2O2 being the major reactive species. Moreover, XP-A cells are characterized by decreased reduced glutathione (GSH)/oxidized glutathione (GSSG) ratios as compared to normal fibroblasts. The significant increase of ROS levels and the alteration of the glutathione redox state following silencing of XPA confirmed the causal relationship between a functional XPA and the control of redox balance. Proton nuclear magnetic resonance ((1)H NMR) analysis of the metabolic profile revealed a more glycolytic metabolism and higher ATP levels in XP-A than in normal primary fibroblasts. This perturbation of bioenergetics is associated with different morphology and response of mitochondria to targeted toxicants. In line with cancer susceptibility, XP-A primary fibroblasts showed increased spontaneous micronuclei (MN) frequency, a hallmark of cancer risk. The increased MN frequency was not affected by inhibition of ROS to normal levels by N-acetyl-l-cysteine.
Journal of the autonomic nervous system, 1990
Journal of the Autonomic Nervous System, 1990
Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1991
We are investigating the cellular and molecular mechanisms involved in the actions of psychoactiv... more We are investigating the cellular and molecular mechanisms involved in the actions of psychoactive drugs. Many of these agents have been found to have selective actions on the function of neurotransmitter-gated ion channels. Moreover, the molecular mechanisms of these actions appear to differ for different agents at different ion channels. In view of the important role that neurotransmitter-gated ion channels
Pharmacological Research, 1990
The electrophysiological effects of BBR 2160 have been studied in multicellular preparations [IJ.... more The electrophysiological effects of BBR 2160 have been studied in multicellular preparations [IJ. BBR 2160 was able to depress calcium-dependent action potentials, suggesting that its negative inotropic effect could be due to its calcium antagonistic properties. The action of the drug appeared to be quite selective, since it did not affect the maximum rate of depolarization (a good index of the Na+ current) of normally polarized sheep Purkinje fibers or guinea-pig papillary muscles. The aim of the present study was to characterize the effect of BBR 2160 on the L-type Ca++ current (I Ca)' in order to get insight into its interaction with the Ca++ channel.
Journal of Neuropathology and Experimental Neurology, 2011
Journal of Molecular and Cellular Cardiology, 1986
Increasing evidence suggests that calcium dependent oscillatory afterpotentials (OAP) may play a ... more Increasing evidence suggests that calcium dependent oscillatory afterpotentials (OAP) may play a pivotal role in the genesis of reperfusion-induced arrhythmias [2, 6, 11, 131. Many factors may influence the vulnerability of the heart to reperfusion arrhythmias, [5, 9] some of which may possibly affect the development of OAP. Since intramyocardial temperature changes during ischemia and reperfusion [7], it may be speculated that the rapid rewarming of the ischemic area during reperfusion favors the development of associated arrhythmias. We thought it important to examine the effects of sudden changes in temperature on OAP and subsequent triggered activity. Evidence is presented that raising the bath temperature from 34~ to 37~ causes a transient increase above the control level of the OAP amplitude, and that if the OAP is large enough to reach the threshold a triggered rhythm ensues. These results suggest that sudden rewa~i~ing of calcium overloaded cell (as it happens during reperfusion of the ischemic myocardium) may favor the development of abnormal automaticity due to OAP.
Journal of Cardiovascular Pharmacology, 1990
Lacidipine is a new 1,4-dihydropyridine derivative with potent and long-lasting antihypertensive ... more Lacidipine is a new 1,4-dihydropyridine derivative with potent and long-lasting antihypertensive activity. We used intracellular microelectrodes to characterize the electrophysiologic properties of lacidipine on different cardiac preparations. Lacidipine (10(-8) -10(-6) M) dose-dependently decreased contractility of driven sheep Purkinje fibers. For concentrations less than or equal to 10(-7) M, this effect was associated with a selective decrease of the plateau height. Higher concentrations (3 X 10(-7) and 10(-6) M), however, affected action potential amplitude, overshoot, and maximum rate of depolarization. In the same range of concentrations, lacidipine did not affect normal automaticity of guinea-pig sinus node and sheep Purkinje fibers. Lacidipine (10(-6) M) consistently blocked barium-induced abnormal automaticity in Purkinje fibers and reduced the amplitude and Vmax of the slow action potentials induced by histamine (10(-5) M) in guinea pig papillary muscle depolarized by potassium (22 mM). The effect of lacidipine on the slow inward current (Isi) was studied in shortened Purkinje fibers under voltage-clamp conditions. Lacidipine (10(-7)-10(-6) M) reduced the Isi without affecting the I-V relationship. None of the effects of lacidipine was reversed by 2-h washout. The results indicate that lacidipine has calcium-antagonistic properties in cardiac tissues. Its cardiac effects occur at concentrations 100 times higher than those active in the vascular smooth muscle. The lack of recovery of the lacidipine effects suggests that its interaction with the calcium channel may occur at an inner site of the cell membrane.
Cardiovascular Drugs and Therapy, 1987
We studied the electrophysiological effects of the specific [32-agonist tulobuterol in the guinea... more We studied the electrophysiological effects of the specific [32-agonist tulobuterol in the guinea-pig sinus node and in sheep cardiac Purkinje fibers. Stimulation of 132-adrenoce ptots by tulobuterol resulted in a slight increase in the rate of firing of the sinus node. In Purkinje fibers, however, automaticity was not affected up to eoncentratmns of 10 M. Consistently, -g -{ . tulobuterol (10 -10 M) d d not affect the pacemaker current studied under voltage-clamp conditions. In the same range of concentrations (I0 -a-i0 -~ M) tulobuterol dose-dependently increased the contractile force of driven Purkinje fibers. Tulobuterol, at a very high concentration (10 -5 M), had membrane depressant effects as demonstrated by the block of automaticity induced in the spontaneously beating Purkinje fibers and by the reduction of the maximum rate of depolarization in driven preparations.
Human molecular genetics, Jan 9, 2016
Mutations in the MLC1 gene, which encodes a protein expressed in brain astrocytes, are the leadin... more Mutations in the MLC1 gene, which encodes a protein expressed in brain astrocytes, are the leading cause of MLC, a rare leukodystrophy characterized by macrocephaly, brain edema, subcortical cysts, myelin and astrocyte vacuolation. Although recent studies indicate that MLC1 protein is implicated in the regulation of cell volume changes, the exact role of MLC1 in brain physiology and in the pathogenesis of MLC disease remains to be clarified. In preliminary experiments, we observed that MLC1 was poorly expressed in highly proliferating astrocytoma cells when compared with primary astrocytes, and that modulation of MLC1 expression influenced astrocyte growth. Because volume changes are key events in cell proliferation and during brain development MLC1 expression is inversely correlated to astrocyte progenitor proliferation levels, we investigated the possible role for MLC1 in the control of astrocyte proliferation. We found that overexpression of wild type but not mutant MLC1 in human...
Journal of neurochemistry, Jan 14, 2015
Microglial activation is a dynamic process, central to neuroinflammation, which can have benefici... more Microglial activation is a dynamic process, central to neuroinflammation, which can have beneficial or pathogenic effects to human health. Mitochondria are key players in neuroinflammatory and neurodegenerative processes, common to most brain diseases. To the best of our knowledge on the role of mitochondria in the modulation of neuroinflammation, we focused on the mitochondrial uncoupling protein-2 (UCP2), known to control mitochondrial functions and to be implicated in a variety of physiological and pathological processes. In primary microglial cultures, the M1 stimulus lipopolysaccharide induced an early and transitory decrease in UCP2 levels. The initial UCP2 down-regulation was paralleled by mitochondrial inner membrane potential (mMP) depolarization and increased mitochondrial reactive oxygen species production. The key role of UCP2 in controlling mMP and reactive oxygen species production was confirmed by both pharmacological inhibition and down-regulation by RNA interference...
Human molecular genetics, Jan 15, 2012
Megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare leukodystrophy character... more Megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare leukodystrophy characterized by macrocephaly, subcortical fluid cysts and myelin vacuolation, has been linked to mutations in the MLC1 gene. This gene encodes a membrane protein that is highly expressed in astrocytes. Based on MLC pathological features, it was proposed that astrocyte-mediated defects in ion and fluid homeostasis could account for the alterations observed in MLC-affected brains. However, the role of MLC1 and the effects of pathological mutations on astrocyte osmoregulatory functions have still to be demonstrated. Using human astrocytoma cells stably overexpressing wild-type MLC1 or three known MLC-associated pathological mutations, we investigated MLC1 involvement in astrocyte reaction to osmotic changes using biochemical, dynamic video imaging and immunofluorescence techniques. We have found that MLC1 overexpressed in astrocytoma cells is mainly localized in the plasma membrane, is part of the ...
The Journal of Physiology, 1999
Uploads
Papers by Sergio Visentin