EXPRESSION OF LOW-VOLTAGE ACTIVATED CA2+ CHANNELS FROM RAT-BRAIN NEURONS IN XENOPUS OOCYTES

XENOPUS laevis oocytes were injected with total mRNA obtained from the thalamo-hypothalamic complex of adult rats. In 19 out of 32 injected oocytes a Ba2+ current was expressed after 4 days which could be activated at depolarizations to -70 mV from a holding potential of -120 mV and reached a maximum value at between -30 and -20 mV. The current inactivated monoexponentially with a time constant of about 420 +/- 10 ms (n = 6); its steady state inactivation had a half value of -78 +/- 1 mV (n = 8) and a slope (k) of 11.5 +/- 3.0. These characteristics are typical of LVA (T-type) Ca2+ channels in neurones from the corresponding brain structures, except for the much slower time course of inactivation. These currents were blocked by pharmacological antagonists specific for LVA channels (amiloride, flunarizine), but remained resistant to omega-Aga-IVA and omega-Cg-toxin. These results show that LVA Ca2+ channels can be expressed in oocytes provided that the corresponding mRNA is taken from brain neurones in which they are naturally well expressed.