177,458 research outputs found
Sturani Ludovico
No full textVoce del Dizionario Biografico degli Italiani relativa a Sturani Ludovico (1778-1836
Serum induces the immediate opening of Ca2+-activated channels in quiescent human fibroblasts.
No full textApplication of fetal calf serum to quiescent human fibroblasts produces an immediate (3-20 s delay) increase in membrane conductance which lasts about 20-30 s. This conductance is strongly outwardly-rectifying and has a reversal potential between -45 and -10 mV. The conductance increase may also be induced by application of the Ca2+ ionophore A23187 while it does not occur when intracellular K+ is replaced by Cs+. It is concluded that this early effect of serum is due to the opening of Ca2+-activated channels. This permeability change will alter the membrane potential and thus possibly interact with other voltage-sensitive processes induced by serum growth factors
Properties of the voltage-dependent calcium channel of mouse Swiss 3T3 fibroblasts.
No full text1. Suspended Swiss 3T3 fibroblasts were voltage clamped using the whole-cell technique. 2. Passage from the cell-attached to the whole-cell mode was accompanied by only a minor decrease in input resistance. Direct measurement of resting potential gave values between O and -15 mV. 3. In order to account for the effects of leak on the membrane potential measurements, I-V curves were obtained immediately before and after patch rupture by applying voltage ramps. After subtraction of the cell-attached current from the whole-cell current, the true membrane potential was estimated as the zero-current potential in the I-V curve. An average value of -8.2 +/- 0.9 mV in 8 mM-Ca2+ was obtained in this way. 4. In 2 mM-Ca2+, step depolarizations 100 ms long from holding potentials (Vh) more negative than -60 mV caused a transient inward current to appear. From Vh greater than -60 mV only a linear leakage component was apparent. 5. In 2 mM-Ca2+ depolarizations to potentials greater than +40 mV (from Vh = -100 mV) generated transient, outwardly directed currents. 6. Increasing extracellular Ca2+ up to 32 mM shifted the peak current vs. voltage curve and the reversal potential (Erev) towards more positive potentials, and caused an increase of the peak current. 7. The steady-state inactivation curve was the same for both inward and outward currents, indicating that they flow through the same channels. The currents are completely inactivated at V = -60 mV. 8. Recovery of the fully inactivated current upon hyperpolarization had an exponential time course with tau = 0.22 s at V = -80 mV and tau = 0.18 s at V = -100 mV. 9. In the absence of Ca2+ (but with Mg2+ present) the inward current disappeared but a large, inactivating outward current appeared when V greater than 0 mV. The current was strongly reduced by Cd2+ (1 mM) or Co2+ (10 mM). 10. Complete removal of divalent cations from the external solution caused the channel to become highly permeable to monovalent cations. 11. Nitrendipine (10 microM) and verapamil (5 microM) were unable to block the current. 12. On the whole the present results indicate that voltage-dependent Ca2+ channels are present in these cells. Their sensitivity to divalent cations, to organic blockers and to potential is similar to that of the low-voltage-activated, or 'T' type, Ca2+ channels described in other cells
Depolarization-induced signaling to Ras, Rap1 and MAPKs in cortical neurons
No full textIn neurons, membrane depolarization triggers pleiotropic signaling which includes the activation of the small GTPases, Ras and Rap1, and the mitogen-activated protein kinases (MAPKs) Erk1/2. We have studied the intracellular signaling mechanisms which regulate these events in mouse-cultured cortical neurons. We show that depolarization induces activation of both Ras and Rap1, although with different kinetics: Ras activation is strong and fast while Rap1 activation is slower and weaker. Blockade of calmodulin affects the GTP-loading of Ras and Rap1 and prevents the MAPK response. Moreover, protein kinase A (PKA) activity is required for depolarization-induced Rap1 activation and full Erk stimulation, but is not involved in that of Ras. This PKA-dependent Rap1 activation does not require Src family kinases, but, in contrast to Ras, is sensitive to genistein, indicating the involvement of a tyrosine kinase-dependent mechanism. Our data provide new insights into the regulation of Ras and Rap1 activation in neurons
Voltage-dependent calcium current in adherent mouse 3T3 fibroblasts.
No full textWhole-cell recording was performed on adherent mouse Swiss 3T3 fibroblasts. Depolarizations from a holding potential of -100 mV gave rise to a transient inward current. The voltage dependence, kinetic properties, and ionic selectivity of this current are identical to those described in the same cells kept in suspension after detachment from the culture dish [A. Pandiella, A. Malgaroli, J. Meldolesi, and L.M. Vicentini (1987) Exp. Cell. Res. 170, 175-185; W.H. Moolenaar, L.G.J. Tertoolen, and S.W. de Laat (1984) J. Biol. Chem. 259
Higgs-graviscalar mixing in type I string theory
No full textWe investigate the possibility of mixing between open and closed string excitations in D-brane models with the fundamental string scale at the TeV. The open string modes describe the Standard Model Higgs, while closed strings describe graviscalars living in the bulk. This provides a string setup for computing the Higgs-graviscalar mixing, that leads to a phenomenologically interesting invisible width of the Higgs in low scale quantum gravity models, as suggested previously by Giudice, Rattazzi and Wells.We investigate the possibility of mixing between open and closed string excitations in D-brane models with the fundamental string scale at the TeV. The open string modes describe the Standard Model Higgs, while closed strings describe graviscalars living in the bulk. This provides a string setup for computing the Higgs-graviscalar mixing, that leads to a phenomenologically interesting invisible width of the Higgs in low scale quantum gravity models, as suggested previously by Giudice, Rattazzi and Wells
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