Two types of pharmacologically distinct Ca(2+) currents with voltage-dependent similarities in zona fasciculata cells isolated from bovine adrenal gland.
Voltage-activated Ca(2+) currents, in zona fasciculata cells isolated from calf adrenal gland, were characterized using perforated patch-clamp recording. In control solution (Ca(2+): 2.5 mm) a transient inward current was followed, in 40% of the cells, by a sustained one. In 20 mm Ba(2+), 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 Ba(2+) than in Sr(2+) and Ca(2+). Ni(2+) (20 microm) selectively blocked the transient component while Cd(2+) (10 microm) selectively blocked the sustained one. (+/-)Bay K 8644 (0.5 microm) increased the sustained component and nitrendipine (0.5-1 microm) blocked it selectively. The sustained component was inhibited by calciseptine (1 microm). Both components were unaffected by omega-conotoxin GVIA and MVIIC (0.5 microm). These results show that two distinct populations of Ca(2+) 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.
Guyot
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A
Université Claude Bernard Lyon I, Laboratoire de Physiologie des Eléments Excitables, UMR CNRS 5578, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.
Dupré-Aucouturier
S
S
Ojeda
C
C
Rougier
O
O
Bilbaut
A
A
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000311:Adrenal Glands / Q000378:metabolism*; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020747:Calcium Channels, T-Type / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D008564:Membrane Potentials; D009532:Nickel / Q000494:pharmacology; D009568:Nitrendipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015383:Zona Fasciculata / Q000378:metabolism*
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D002104:Cadmium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009532:Nickel; D009568:Nitrendipine; D002118:Calcium