[Action of omega-conotoxin on calcium currents of the rat pituitary GH3 cell line]

Whole-cell modification of the patch clamp method was used to examine the action of omega-CgTX on calcium currents in GH3 pituitary cells. Two quite distinct components of inward calcium currents were observed in the presence of 15 mmol/l of calcium in the external solution. One was activated from the holding potential -80 mV by testing pulses more positive than -50 mV. The shift of the holding potential to -40 mV resulted in the stationary inactivation of this low voltage activated current component. It was found that omega-CgTX activated both low-threshold and high-threshold calcium currents at the first moment of application, but low-threshold current component increased more significantly. Full effect was developed for less than 30 s. Then time decay of currents was comparable with that of the "wash-out" process. Incubation of cells in the growth medium that contained 5 mumol/l omega-CgTX during 2 hour induced an increase in density of both types of calcium currents, then it fell after 2 hours of incubation in the same medium.