1,720,971 research outputs found
Analisi cinetica di una corrente potassio transiente nelle cellule dei granuli di cervelletto di ratto "in vitro"
No full textCaratterizzazione delle correnti voltaggio-dipendenti mediate dal potassio nelle cellule dei granuli del cervellett
Azione modulatrice dello zinco extracellulare sulla corrente potassio transiente in cellule dei granuli di cervelletto di ratto
No full textCaratterizzazione dell'azione modulatoria dello ione zinco sulle proprietà di voltaggio-dipendenza della corrente potassio nelle cellule dei granuli del cervellett
Kinetic study and numerical reconstruction of A-type current in granule cells of rat cerebellar slices
No full text1. Whole-cell voltage-clamp techniques were used to study voltage-activated transient potassium currents in a large sample (n = 143) of granule cells (GrC) from rat cerebellar slices. Tetrodotoxin (TTX; 0.1 microM) was used to block sodium currents, while calcium current was too small to be seen under ordinary conditions. 2. Depolarizing pulses from -50 mV evoked a slow, sustained outward current, developing with a time constant of 10 ms, inactivating over a time scale of seconds and which could be suppressed by 20 mM tetraethylammonium (TEA). By preventing the Ca2+ inflow, this slow outward current could be further separated into a Ca(2+)-dependent and a Ca(2+)-independent component. 3. After conditioning hyperpolarizations to potentials negative to -60 mV, depolarizations elicited transient outward current, peaking in 1-2 ms and inactivating rapidly (approximately 10 ms at 20 degrees C), showing the overall kinetic characteristics of the A-current (IA). The current activated following third-order kinetics and showed a maximal conductance of 12 nS per cell, corresponding to a normalized conductance of 3.8 nS/pF. 4. IA was insensitive to TEA and to the Ca(2+)-channel blockers. 4-Aminopyridine (4-AP) reduced the A-current amplitude by approximately 20%, and the delayed outward currents by > 80%. 5. Voltage-dependent steady-state inactivation of peak IA was described by a Boltzmann function with a slope factor of 8.4 mV and half-inactivation occurring at -78.8 mV. Activation of IA was characterized by a Boltzmann curve with the midpoint at -46.7 mV and with a slope factor of 19.8 mV. 6. IA activation and inactivation was best fitted by the Hodgkin-Huxley m3h formalism. The rate of activation, tau a, was voltage-dependent, and had values ranging from 0.55 ms at -40 mV to 0.2 ms at +50 mV. Double-pulse experiment showed that development and removal of inactivation followed a single-exponential time course; the inactivation time constant, tau ha, was markedly voltage-dependent and ranged from approximately 10 ms at -40 and -100 mV and 70 ms at -70 mV. 7. A set of continuous equations has been developed describing the voltage-dependence of both the steady-state and time constant of activation and inactivation processes, allowing a satisfactory numerical reconstruction of the A-current over the physiologically significant membrane voltage rang
Excitatory synapses in the glomerular triad of frog olfactory bulb in vitro
No full textWHOLE-CELL patch clamp recording techniques were applied to periglomerular (PG) cells in slices of the frog olfactory bulb (OB) to study the properties of the excitatory synapses in the triad formed by the olfactory nerve (ON) and the dendrites of mitral/tufted (MT) cells and PG cells. The postsynaptic response evoked by ON stymulation was glutamatergic and could be dissected into NMDA and non-NMDA components of equivalent amplitudes. The dendro-dendritic synapse between MT and PG cells could be activated following antidromic stimulation of the lateral and medial olfactory tract (LOT and MOT). In this case the postsynaptic potentials had amplitudes and durations comparable to those obtained by ON stimulation, the neurotransmitter was glutamate, but the synapse was largely dominated by the slow NMDA component
Potassium currents in periglomerular cells of frog olfactory bulb in vitro
No full textVoltage-activated currents have been recorded from periglomerular cells in thin slices of frog olfactory bulb. Cells were examined with whole-cell patch clamp methods. The voltage-dependent potassium currents were studied after pharmacological block of inward currents. Depolarising steps from -130 mV gave an early transient, A-type, outward current and a delayed rectifier K+ current (IKV). The two currents could be isolated on the basis of the differences in their kinetic properties. The A-current developed following a third-order kinetics when the membrane was depolarised to potentials more positive than -40 mV after preconditioning to potentials more negative than -60 mV. Once activated (tau a 2.5 ms at 0 mV), IA inactivated following a single exponential (tau ha about 60 ms). IKV activated with a second-order kinetics above -30 mV with a time constant of 4 ms at 0 mV. IA and IKV were sensitive, respectively, to 4-aminopyridine (4-AP) and tetraethylammonium (TEA)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Sodium current in periglomerular cells of frog olfactory bulb in vitro
No full textKinetic properties of the sodium current in periglomerular (PG) cells were investigated by applying whole-cell patch-clamp techniques to thin slices of the frog olfactory bulb. Eight of the cells were intracellularly stained with Lucifer Yellow for precise identification. Under current-clamp conditions PG cells showed rich spontaneous activity at rest. Na current was isolated from other current contributions by equimolar substitution of K+ with Cs+ in the intracellular solution to prevent K-currents, and 100 microM Cd2+ in the external solution to block Ca-current. Depolarisations beyond -40 mV activated a fast transient TTX-sensitive inward current. Once activated, INa declined exponentially to zero following a single exponential. The underlying conductance showed a sigmoidal activation between -40 and +30 mV, with half activation at -17.4 mV and a maximal value of 9.7 nS per neurone. The steady-state inactivation was complete at -30 mV and completely removed at -90 mV, with a midpoint at -56 mV. The activation process could be adequately described by third order kinetics, with time constants ranging from 260 microseconds at -20 mV to 70 microseconds at +50 mV
Electrical properties of periglomerular cells in the frog olfactory bulb.
No full textWhole-cell patch clamp recording techniques were applied to periglomerular (PG) cells in slices of the frog olfactory bulb (OB) preparation to study the basic electrical properties of these inhibitory interneurons. The cells were intracellularly stained with Lucifer Yellow for precise identification. Under current-clamp conditions PG cells showed rich spontaneous excitatory synaptic activity at rest, usually leading to overshooting, TTX-sensitive action potentials. The passive cable properties of the cell membrane have been carefully characterised. Depolarisation of this neurone under voltage-clamp conditions activated a complex pattern of current flow, that has been dissected into its main components. The currents have been isolated resorting to their different kinetic and pharmacological properties. Four main voltage dependent ionic currents have been isolated, two inward currents, I(Na) and I(Ca), and two outward currents carried by potassium ions, one fast transient, I(A)-type and another similar to the delayed rectifier type. These currents have been characterised kinetically and pharmacologically. The functional implications of their properties are discussed
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