Ca²⁺Influx through Mechanosensitive Channels Inhibits Neurite Outgrowth in Opposition to Other Influx Pathways and Release from Intracellular Stores

Abstract

Ca2ϩ signals are known to be important regulators of neurite outgrowth and steering. Here we show that inhibiting Ca 2ϩ influx through stretch-activated channels using various compounds, including a highly specific peptide isolated from Grammostola spatulata spider venom (GsMTx4), strongly accelerates the rate of neurite extension on diverse substrata and within the intact spinal cord. Consistent with the presence of stretch-activated channels, we show that Ca 2ϩ influx is triggered by hypotonic solutions, which can be partially blocked by GsMTx4. Finally, chelating local, but not global, Ca 2ϩ signals prevents the acceleration that is normally produced by GsMTx4. Blocking Ca 2ϩ influx through other channel types has little or opposite effects, but release from intracellular stores is required for maximal acceleration. Together, our data suggest that Ca 2ϩ functions at distinct microdomains in growth cones, with influx through mechanosensitive channels acting to inhibit outgrowth in opposition to influx through other plasma membrane channels and release from stores.

Calcium signaling in axon guidance

“…Tojima et al [17] found that calcium entry involving CICR and IICR produced an attractive response, whereas Ca 2+ signals without store entry invoked a repulsive response [17]. Furthermore, the method of calcium entry also affects axon outgrowth and growth cone motility [40,41]. Calcium influx through mechanosensitive stretch-activated channels decreases axon motility [41].…”

“…Furthermore, the method of calcium entry also affects axon outgrowth and growth cone motility [40,41]. Calcium influx through mechanosensitive stretch-activated channels decreases axon motility [41]. By contrast, calcium influx through other avenues (TRPC channels and intracellular stores) supports and promotes axon outgrowth [41].…”

“…Calcium influx through mechanosensitive stretch-activated channels decreases axon motility [41]. By contrast, calcium influx through other avenues (TRPC channels and intracellular stores) supports and promotes axon outgrowth [41]. It is unclear whether these outcomes are specifically related to the source of Ca 2+ or simply to the resulting elevation -which is known to have narrow ranges which result in attraction [42] and increased axon outgrowth [43].…”

“…Calcium signaling has an effect on the growth rate of growth cones, first characterized as a narrow extracellular calcium concentration range favorable for growth [43,[60][61][62]. Surprisingly, calcium transients [63,64] and calcium entry through mechanosensitive channels slow axon growth, whereas calcium release from ER stores enhances growth [41]. The relation between calcium transients and cAMP signaling may be different between the central domain of the growth cone and its filopodia [19].…”

Calcium Signaling in Neuronal Motility: Pharmacological Tools for Investigating Specific Pathways

“…However, most of these effects have been observed at concentrations in the 10-100 µM range, while at concentrations of 5 µM or lower it can be considered a good preliminary tool to block TRPC-mediated influx. The lack of better options can explain its continued use in many studies, in particular in the field of neurite growth and orientation [80,85,86]. Inorganic ions, such as La 3+ (and Gd 3+ ), can block most of these channels [87], but with complex dose-response relationships; therefore, these tools have to be employed with caution.…”