Two Types of Pharmacologically Distinct Ca2+ Currents with Voltage-dependent Similarities in Zona Fasciculata Cells Isolated from Bovine Adrenal Gland |
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Authors: | A Guyot S Dupré-Aucouturier C Ojeda O Rougier A Bilbaut |
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Institution: | (1) Université Claude Bernard Lyon I, Laboratoire de Physiologie des Eléments Excitables, UMR CNRS 5578, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France, FR;(2) INSERM, U 121, 18 Avenue du Doyen Lépine, 69500 Bron, France, FR |
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Abstract: | Voltage-activated Ca2+ currents, in zona fasciculata cells isolated from calf adrenal gland, were characterized using perforated patch-clamp recording.
In control solution (Ca2+: 2.5 mm) a transient inward current was followed, in 40% of the cells, by a sustained one. In 20 mm Ba2+, 61% of the cells displayed an inward current, which consisted of transient and sustained components. The other cells produced
either a sustained or a transient inward current. These different patterns were dependent upon time in culture. Current-voltage
relationships show that both the transient and sustained components activated, peaked and reversed at similar potentials:
−40, 0 and +60 mV, respectively. The two components, fully inactivated at −10 mV, were separated by double-pulse protocols
from different holding potentials where the transient component could be inactivated or reactivated. The decaying phase of
the sustained component was fitted by a double exponential (time constants: 1.9 and 20 sec at +10 mV); that of the transient
component was fitted by a single exponential (time constant: 19 msec at +10 mV). Steady-state activation and inactivation
curves of the two components were superimposed. Their half activation and inactivation potentials were similar, about −15
and −34 mV, respectively. The sustained component was larger in Ba2+ than in Sr2+ and Ca2+. Ni2+ (20 μm) selectively blocked the transient component while Cd2+ (10 μm) selectively blocked the sustained one. (±)Bay K 8644 (0.5 μm) increased the sustained component and nitrendipine (0.5–1 μm) blocked it selectively. The sustained component was inhibited by calciseptine (1 μm). Both components were unaffected by ω-conotoxin GVIA and MVIIC (0.5 μm). These results show that two distinct populations of Ca2+ channels coexist in this cell type. Although the voltage dependence of their activation and inactivation are comparable,
these two components of the inward current are similar to T- and L-type currents described in other cells.
Received: 12 July 1999/Revised: 5 October 1999 |
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Keywords: | : Adrenal cells — Ca2+ channel types — Voltage-dependence — Pharmacology |
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