Injected inositol 1,4,5-trisphosphate activates Ca2(+)-sensitive K+ channels in the plasmalemma of Eremosphaera viridis.

InsP3, and established mediator of intracellular Ca2+ signals in animal cells, is microinjected into the cytoplasm of Eremosphaera viridis. InsP3, but not Ins, InsP1, InsP2 or F2,6-P2 induce a transient opening of Ca2(+)-dependent K+ channels in the plasmalemma of this alga. This effect is indicated by a transient polarization (TP) with a simultaneous increase of membrane conductance. The TP is inhibited by TMB8 (2 mM), an intracellular Ca2+ antagonist or by BAPTA (20 mM), microinjected together with InsP3. The results suggest that InsP3 initiates an increase in the cytoplasmic Ca2+ activity and an activation of Ca2(+)-dependent membrane currents, hence, opening of K+ channels.