Expression of a rapidly inactivating Ca2+ channel in Pleurodeles oocytes during the resting season

Two kinds of Ca2+ channel activities have been recorded in unfertilized Pleurodeles oocytes during the resting season: the previously described L-type and a transient one. The transient Ba current (I(Ba-t)) exhibited a voltage threshold of -36+/-7 mV, peaked at -18+/-8 mV and reversed around +50 mV. It showed a fast monoexponential decay with an inactivation time course of 31.4+/-1.7 ms at -20 mV. I(Ba-t) was insensitive to nifedipine and omega-conotoxin-GVIA but blocked by Ni2+ (50 microM). Moreover, Cd2+ also reduced I(Ba-t) but was less efficient than Ni2+. When using Ca2+ as the charge carrier, the amplitude and the decay of I(ca-t) were largely similar to those of I(Ba-t). These data demonstrated that the population of Ca2+ channels could be seasonally modulated in Pleurodeles oocytes.