Calcium channel upregulation in response to activation of neurotrophin and surrogate neurotrophin receptor tyrosine kinases

✍ Scribed by Melony J. Black; Yeunkyung Woo; Stanley G. Rane

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 434 KB
• Volume: 74
• Category: Article
• ISSN: 0360-4012
• DOI: 10.1002/jnr.10748

✦ Synopsis

Abstract

Modulation of calcium channel expression and function in the context of neurotrophin induced neuronal differentiation remains incompletely understood at a mechanistic level. We addressed this issue in the PC12 model neuronal system using patch clamp electrophysiology combined with ectopic expression of the human β platelet‐derived growth factor (βPDGF) receptor as a surrogate neurotrophin receptor system. PC12 cells ectopically expressing the human βPDGF receptor were treated with PDGF or nerve growth factor (NGF) for up to 7 days, and Ca^2+^ channel subtype expression was analyzed using selective pharmacological agents in both whole‐cell and cell‐attached single channel patch clamp configurations. PDGF‐induced upregulation of N‐ and P/Q‐type Ca^2+^ channel currents completely mimicked upregulation of these currents caused by NGF stimulation of the endogenous TrkA receptor tyrosine kinase (RTK). Neither PDGF nor NGF significantly altered L‐ or R‐type currents. Single channel recordings together with immunocytochemistry implied that growth factor‐induced increases in whole‐cell Ca^2+^ currents were a result of synthesis of new channels, and that whereas increased N channel density was apparent in the soma, additional P/Q channels distributed preferentially to extrasomal locations, most likely the proximal neurites. Finally, specific signaling‐deficient mutant forms of the βPDGF receptor were used to show that activation of Src, PI3‐kinase, RasGAP, PLCγ or SHP‐2 (some of which are implicated in certain other aspects of PC12 cell differentiation) by RTKs is not required for growth factor‐induced Ca^2+^ channel upregulation. In contrast, activation of the Ras‐related G‐protein Rap1 was found critical to this process. © 2003 Wiley‐Liss, Inc.