Phorbol ester and calcium act synergistically to enhance neurotransmitter release by brain neurons in culture

Preincubation of intact fetal brain neurons in culture with the phorbol ester TPA (12-O-tetradecanoyl phorbol-13-acetate) in the presence of calcium, resulted in the enhancement of the depolarization-induced, Ca²⁺-dependent neurotransmitter release by the cells. This effect was due to a marked decrease in the concentration of extracellular Ca²⁺ required to provoke the release. The concentration of Ca²⁺ needed to produce half-maximal release shifted from approx 0.1 mM in the absence of TPA to 0.018 mM in its presence. This activity of TPA was concentration-dependent (half-maximal effect at 4 nM TPA) and was also dependent on the presence of calcium during the preincubation period. The TPA-induced enhancement of the stimulated release was also observed when Ca²⁺ entry into the depolarized cells was partially inhibited by Co²⁺. The results suggest that TPA acts synergistically with Ca²⁺ to activate neuronal component(s) involved in Ca²⁺-dependent neurosecretion. Phorbol ester Calcium Brain neuron Neurotransmitter.