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We have determined the time course of Na channel inactivation in clonal pituitary (GH3) cells by comparing records before and after the enzymatic removal of inactivation. The cells were subjected to whole-cell patch clamp, with papain included in the internal medium. Inactivation was slowly removed over the course of 10 min, making it possible to obtain(More)
Ca channel currents in primary cultured pars intermedia cells were studied using whole-cell recording with patch pipettes. Experiments were carried out at 18-21 degrees C in cells internally dialyzed with K-free, EGTA-containing solutions and in the presence of 10 mM Ca or 10 mM Ba in the external solution. Ca and Ba currents depended on the activity of two(More)
In rat pituitary GH3 cells, epidermal growth factor (EGF) and insulin stimulate prolactin production, whereas glucocorticoids exert the opposite effect. In the present study, GH3 cells were subjected to whole-cell patch clamp to assess the chronic actions of such regulatory factors on voltage-dependent calcium currents. Before the electrical recording,(More)
Voltage-clamp and current-clamp experiments were performed to study Ca2+ and Ba2+ permeation through Ca channels in intact twitch skeletal muscle fibres of the frog. Surface charge effects were taken into consideration. Ca2+ (ICa) or Ba2+ (IBa) currents, or Ca2+ and Ba2+ action potentials were recorded in the presence of external tetraethylammonium (TEA+)(More)
Calcium ions in the external medium stabilize the resting state of voltage-dependent channels, including Na channels. This effect of calcium on channel gating is usually explained in terms of the surface charge hypothesis, which proposes that local adsorption of calcium ion to the outside of the membrane alters the intramembranous electric field, thus(More)
We have studied the potassium currents of rat pituitary pars intermedia cells kept in primary culture using whole-cell recording with patch pipettes. The potassium current recorded with hard-glass pipettes is mainly carried by voltage-dependent channels that show slow inactivation in the presence of 0.5 mM internal EGTA. Fast "inactivation" of the potassium(More)
1. The amplitude and time course of K contractures (Cl- constant) of single twitch muscle fibres of the frog have been analysed in three external Ca2+ concentrations. 2. The resting potential, effective resistance, threshold for the Na current and K-induced depolarizations were not modified by replacing 1.8 mM-Ca2+ by 3 mM-Mg2+ in absence (low-Ca saline:(More)
In clonal pituitary GH(3) cells, spontaneous action potentials drive the opening of Ca(v)1 (L-type) channels, leading to Ca(2+) transients that are coupled to prolactin gene transcription. Nerve growth factor (NGF) has been shown to stimulate prolactin synthesis by GH(3) cells, but the underlying mechanisms are unknown. Here we studied whether NGF(More)
Calcium ion transiently blocks Na+ channels, and it shortens the time course for closing of their activation gates. We examined the relation between block and closing kinetics by using the Na+ channels natively expressed in GH3 cells, a clonal line of rat pituitary cells. To simplify analysis, inactivation of the Na+ channels was destroyed by including(More)
In clonal pituitary (GH3) cells we studied the changes in sodium channel gating caused by substitution of La3+ for Ca2+ ion. Gating of sodium channels was simplified by using intracellular papain to remove inactivation. To quantify La effects, we empirically fitted closing and the late phase of opening of the channels with single exponentials, determined(More)