CALPAIN INHIBITORS BLOCK CA2-INDUCED SUPPRESSION OF NEURITE OUTGROWTHIN ISOLATED HIPPOCAMPAL PYRAMIDAL NEURONS()

Ca2+ is an important regulator of neurite elongation and growth cone m ovements but the mechanism(s) mediating these Ca2+-dependent effects i s unclear. Since cytoskeletal proteins are rapidly degraded by Ca2+-de pendent proteinases (calpains) in vitro and in vivo, we investigated w hether Ca2+-induced pruning or regression of neuronal processes is med iated by calpains. Isolated hippocampal pyramidal-like neurons were cu ltured and the ability of the membrane-permeable calpain inhibitors et hyl(+)(2S ,3S)-3-[(S)-methyl-1-(3-methylbutylcarbamoyl)-bu- tylcarbamo yl]-2-oxiranecarboxylate (EST) and carbobenzoxyl-valyl-phenylalanyl-H (MDL 28170) to block the Ca2+ ionophore A23187-induced suppression in neurite outgrowth was investigated. Addition of 100 nM A23187 to the c ulture medium resulted in a retraction of dendrites without altering a xonal elongation. The addition of 300 nM A23187 to the culture medium resulted in a significant decrease in the rate of axonal elongation as well as a retraction of dendritic processes. Administration of EST (5 or 20 mu M) to the culture medium completely blocked the pruning effe ct of 100 nM A23187 on dendrites and of 300 nM A23187 on axons, while EST alone did not significantly affect neurite outgrowth rate. MDL 281 70 (20 mu M) showed the same effect as EST in preventing ionophore-ind uced pruning of dendrites and axons at 100 and 300 nM concentrations, respectively, of A23187. EST (20 mu M) did not block the A23187-induce d rise of [Ca2+](i) as measured with fura-2. These results suggest tha t calpains play a role in Ca2+-induced pruning of neurites in isolated hippocampal pyramidal neurons. (C) 1994 Wiley-Liss, Inc.