MASTOPARAN-INDUCED APOPTOSIS OF CULTURED CEREBELLAR GRANULE NEURONS IS INITIATED BY CALCIUM-RELEASE FROM INTRACELLULAR STORES

We have recently reported that mastoparan, a peptide toxin isolated fr om wasp venom, induces apoptosis in cultured cerebellar granule neuron s that can be blocked by cholera toxin, an activator of G(s). Measurem ents of intracellular free calcium concentration ([Ca2+](i)) reveal th at mastoparan induces a dramatic elevation of [Ca2+](i) that is freque ntly followed by enhanced leakage of fura-2 out of the neurons, sugges ting that this rise in [Ca2+](i) may be due to a more generalized chan ge in membrane permeability. However, the mastoparan-induced initial e levation of [Ca2+](i) is maintained in the absence of extracellular Ca 2+, suggesting that the rise of [Ca2+](i) is from intracellular stores . This conclusion is supported by the observation that depletion of [C a2+](i) stores by pretreatment with either caffeine or thapsigargin at tenuates both the rise in [Ca2+](i) and cell death induced by mastopar an, Phospholipase C (PLC) inhibitors, neomycin and U73122 block mastop aran-induced increases of [Ca2+](i) and protect against neuronal death . Pretreatment with cholera toxin, but not pertussis toxin, reduced th e mastoparan-induced rise in [Ca2+](i). Taken together, our data sugge st that mastoparan initiates cell death in cerebellar granule neurons by inducing Ca2+ release from intracellular stores, probably via activ ation of PLC and IP3. A secondary or parallel process results in disru ption of plasma membrane integrity and may be ultimately responsible f or the death of these neurons by mastoparan. (C) 1997 Elsevier Science B.V.