STUDY OF PHOSPHOINOSITIDE-SPECIFIC PHOSPHOLIPASE-C ACTIVITY IN RABBITNERVE AT REST AND UNDER STIMULATION

The dependence of rabbit sciatic nerve phosphoinositide (PtdIns)-speci fic phospholipase C activity on Ca2+ and pH was studied. The enzyme hy drolyzes PtdInsP(2) in a Ca2+-dependent manner. Maximal enzyme activit y in cytosol and particulate fractions was registered in the presence of 1 and 0.1 mM CaCl2, respectively. Optimal pH values for the enzyme activity of cytosol and particulate fractions were 6.0 and 7.0, respec tively. Nerve stimulation (200 impulse/sec, 5 min) did not influence c ytosol enzyme activity and increased by 44% particulate enzyme activit y compared with the rest. It is suggested that in the intact axons Ptd Ins-specific phospholipase C is bound to membranes therefore the rapid signal transduction (depolarizing stimulus) into axon becomes possibl e at excitation.