Summary of Work: It is well established that controlled elevation of neuronal calcium suppresses apoptosis. Vasoactive intestinal peptide (VIP) has also been reported to promote neuronal survival in vitro and to reduce neuronal death induced by gp120. We hypothesized that many of these effects could be attributed to stimulation of voltage-activated calcium channels through cAMP-dependent protein phosphorylation. We have used the patch clamp to study the effect of the HIV viral coat protein, gp120, on voltage-activated calcium currents in immortalizee cells from the mammalian neuroendocrine system. We have observed that gp120 rapidly and completely blocks L-type calcium channels in rat pituitary tumor cells (GH4C1). Even when the gp120 is applied in the bath, it inhibits the activity of calcium channels in cell-attached patches, an effect that is blocked by inhibition of serine/threonine-directed protein phosphatases with environmental toxins. Because L-type calcium channels require cAMP-dependent protein phosphorylation to respond to membrane depolarization, we are currently investigating the role of protein phosphorylation in the effect of gp120. Dr. Duerson has also demonstrated that second messengers controlling protein phosphatase activity in GH cells mimic the effects of gp120 on calcium channel activity. Dr. Romeo has obtained a plasmid encoding synthetic gp120 with common mammalian codons, which we will use to obtain a homogeneous and reliable supply of the protein for further studies.