Résumé
We characterized toxin-insensitive calcium currents expressed by acutely dissociated embryonic dorsal root ganglion neurons. In the presence of 3
μM
ω-conotoxin-GVIA, 3
μM nitrendipine and either 500
nM
ω-agatoxin-IVA or 500
nM
ω-conotoxin-MVIIC to inhibit N-, L- and P/Q-type currents, respectively, all neurons expressed two residual currents: a T-type and another which we referred to as toxin-resistant current. The toxin-resistant current (i) consisted of an inactivating and a sustained components, (ii) had a threshold of activation and a steady-state inactivation comprised between that of the T-type current and that of the other high-voltage-activated currents, (iii) had the same permeability for barium and calcium used as charge carriers, (iv) was highly sensitive to both cadmium and nickel; and (v) was insensitive to 500
μM amiloride which abolished the T-type at this concentration. The properties of the toxin-resistant current are very similar to those of the currents expressed in oocytes following injection of
α
1E subunits which we demonstrated to be present in these neurons.
Therefore a component of the toxin-resistant current calcium channels in sensory neurons may be closely related to those calcium channels formed by
α
1E subunits.