Sealing of transected neurites of rat B104 cells requires a diacylglycerol PKC-dependent pathway and a PKA-dependent pathway.

To survive, neurons and other eukaryotic cells must rapidly repair (seal) plasmalemmal damage. Such repair occurs by an accumulation of intracellular vesicles at or near the plasmalemmal disruption. Diacylglycerol (DAG)-dependent and cAMP-dependent proteins are involved in many vesicle trafficking pathways. Although recent studies have implicated the signaling molecule cAMP in sealing, no study has investigated how DAG and DAG-dependent proteins affect sealing. By means of dye exclusion to assess Ca(2+)-dependent vesicle-mediated sealing of transected neurites of individually identifiable rat hippocampal B104 cells, we now report that, compared to non-treated controls, sealing probabilities and rates are increased by DAG and cAMP analogs that activate PKC and Munc13-1 and PKA. Sealing is decreased by inhibiting DAG-activated novel protein kinase C isozymes η (nPKCη) and θ (nPKCθ) and Munc13-1, the PKC effector myristoylated alanine rich PKC substrate (MARCKS) or phospholipase C (PLC). DAG-increased sealing is prevented by inhibiting MARCKS or protein kinase A (PKA). Sealing probability is further decreased by simultaneously inhibiting nPKCη, nPKCθ, and PKA. Extracellular Ca(2+), DAG, or cAMP analogs do not affect this decrease in sealing. These and other data suggest that DAG increases sealing through MARCKS and that nPKCη, nPKCθ, and PKA are all required to seal plasmalemmal damage in B104 and likely all eukaryotic cells.

Pathways for plasmalemmal repair mediated by PKA, Epac, and cytosolic oxidation in rat B104 cells in vitro and rat sciatic axons ex vivo.

Plasmalemmal repair (sealing) is necessary for survival of damaged eukaryotic cells. Ca(2+) influx through plasmalemmal disruptions activates pathways that initiate sealing, which is commonly assessed by exclusion of extracellular dye. These sealing pathways include PKA, Epac, and cytosolic oxidation. In this article, we investigate whether PKA, Epac, and/or cytosolic oxidation, activate specific proteins required to produce a plasmalemmal seal. We report that toxin cleavage of proteins required for neurotransmitter release (SNAP-25), inhibition of Golgi trafficking (with Brefeldin A: Bref A) or inhibition of N-ethylmaleimide sensitive factor (NSF) all decrease sealing of rat B104 hippocampal cells with transected neuritis in vitro. Epac, but not PKA or cytosolic oxidation, partly overcomes the decrease in sealing produced by cleavage of SNAP-25. PKA and increased cytosolic oxidation, but not Epac, can partly overcome the decrease in sealing due to Bref A. PKA, Epac, and/or cytosolic oxidation cannot overcome NSF inhibition. Substances that affect plasmalemmal sealing of B104 neurites in vitro have similar effects on plasmalemmal sealing in rat sciatic axons ex vivo. From these and other data, we propose a model of plasmalemmal sealing having three redundant, evolutionarily conserved, parallel pathways that all converge on NSF.