Latrotoxin stimulates secretion in permeabilized cells by regulating an intracellular Ca2+- and ATP-dependent event: A role for protein kinase C

Abstract

α-Latrotoxin, a component of black widow spider venom, stimulates transmitter release from nerve terminals and intact chromaffin cells and enhances secretion from permeabilized chromaffin cells already maximally stimulated by Ca2+. In this study we demonstrate that chromaffin cells contain a protein antigenically similar to the cloned Ca2+-independent receptor for α-latrotoxin. Although this receptor has homology to the secretin family of G-protein-linked receptors, pertussis toxin has no effect on the ability of α-latrotoxin to enhance secretion, suggesting that neither G(i) nor G(o) is involved in the response. Furthermore, in the absence of Ca2+, α-latrotoxin does not stimulate polyphosphoinositide-specific phospholipase C. α-Latrotoxin specifically enhances ATP-dependent secretion in permeabilized cells. An in situ assay for protein kinase C reveals that α-latrotoxin augments the activation of protein kinase C by Ca2+, and use of protein kinase inhibitors demonstrates that this activation is important for the toxin's enhancing effect. This enhancement of secretion requires Ca2+ concentrations above 3 μM and is not supported by Ba2+ or nonhydrolyzable guanine nucleotides, which do not stimulate protein kinase C. We conclude that α-latrotoxin stimulates secretion in permeabilized cells by regulating a Ca2+- and ATP-dependent event involving protein kinase C.