Neomycin and U73122 are known to suppress inositol
1,4,5-trisphosphate (InsP3) production by inhibition of phospholipase
C. We studied the effects of these inhibitors on the
excitatory currents, Iex, in Chara corallina under voltage-clamp
conditions. Computer simulations of the experimental effects by
a minimum model for the excitatory reaction pathway allow the
assignment of the inhibitory effects to one specific reaction step,
i.e. the release of Ca2+ from InsP3-sensitive internal stores. In
contrast, the inhibitory effect of La3+ on Iex suggests inactivation
of Cl3 channels. Furthermore, ryanodine-sensitive Ca2+ stores
seem to be irrelevant for electrical excitation in Chara.
z 1999 Federation of European Biochemical Societies.