EXPRESSION OF A RAPIDLY INACTIVATING CA2+ CHANNEL IN PLEURODELES OOCYTES DURING THE RESTING SEASON

Two kinds of Ca2+ channel activities have been recorded in unfertilize d Pleurodeles oocytes during the resting season: the previously descri bed L-type and a transient one. The transient Ba current (I-Ba-t) exhi bited a voltage threshold of -36+/-7 mV, peaked at -18+/-8 mV and reve rsed around +50 mV. It showed a fast monoexponential decay with an ina ctivation time course of 31.4 +/- 1.7 ms at -20 mV. I-Ba-t was insensi tive to nifedipine and omega-conotoxin-GVIA but blocked by Ni2+ (50 mu M). Moreover, Cd2+ also reduced I-Ba-t but was less efficient than Ni 2+. 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 demonst rated that the population of Ca2+ channels could be seasonally modulat ed in Pleurodeles oocytes.