Ca²⁺ influx through both L‐ and N‐type Ca²⁺ channels increases c‐fos expression by electrical stimulation of sympathetic neurons

Abstract

During direct membrane depolarization, Ca2+ influx primarily through L-type Ca2+ (L-) channels initiates activity-dependent gene transcription. This is surprising given that in most neurons a minority of the total Ca2+ current arises from L-channel activity. However, many studies have stimulated Ca2+ influx with unphysiological stimuli such as chronic membrane depolarization using high K+ medium. Few studies have tested whether other Ca2+ channels stimulate gene transcription in adult neurons as a consequence of direct electrical stimulation. Therefore, we evaluated the role of L- and N-type Ca2+ (N-) channel activity in regulating mRNA levels of c-fos, an activity-dependent transcription factor, in adult rat superior cervical ganglion (SCG) neurons as the majority of Ca2+ channels are N-type, while only a minority are L-type. Changes in c-fos mRNA levels were measured using semi-quantitative and single-cell RT-PCR. Phosphorylation of CREB (pCREB) and changes in c-Fos levels were visualized in dissociated cells by immunocytochemistry. Increases in pCREB, c-fos mRNA and c-Fos protein with either K+ or electrical depolarization required Ca2+ influx. These results support previous findings that elevated c-fos levels result from pCREB stimulating c-fos transcription. Elevation of pCREB, c-fos and c-Fos with K+ depolarization depended on L-channel activity. By contrast, antagonizing either channel at 10-Hz stimulation minimized these increases despite unequal numbers of the two channel types. Transition to exclusive L-channel involvement occurred with increasing frequency of stimulation (from 10 to 20 to 50 Hz). Our results demonstrate that N- and L-channel participation in regulating c-fos expression is encoded in the pattern of electrical stimulation.

Cellular mechanisms of activity-dependent BDNF expression in primary sensory neurons

“…Since CREB can be phosphorylated in response to calcium influx specifically through N-type channels (Wheeler et al, 2012; Zhao et al, 2007), these previous findings together with our current data indicate that repetitive electrical stimulation increases BDNF expression in sensory neurons by activating CREB in response to calcium influx through N-type channels (Fig. 5).…”

Normal dendrite growth in Drosophila motor neurons requires the AP‐1 transcription factor

“…A similar dependence of neuronal growth on calcium channels has been demonstrated convincingly in the Drosophila giant neuron culture system (Peng et al, 2007). Ultimately, it will be important to establish the specific parameters of activity and calcium flux that are essential for modulating the intracellular signals that mediate growth plasticity (Fields et al, 1997; Zhao et al, 2007). …”

“…A key goal for future studies must be to determine how neural activity is translated into transcription factor activity (Fields et al, 1997; Zhao et al, 2007). Calcium dependent signaling is arguably the most important pathway for the activation of both CREB and Mef2A, two transcription factors that influence plasticity in opposite ways (Redmond et al, 2002; Flavell et al, 2006; Shalizi et al, 2006), as well as AP-1 (Zhao et al, 2007).…”

Membrane depolarization inhibits spiral ganglion neurite growth via activation of multiple types of voltage sensitive calcium channels and calpain

“…For example, the route of Ca 2+ entry differs depending on whether cultured sensory neurons are chronically depolarized or electrically stimulated in a pulsatile pattern, being predominantly through L-type VGCCs in the former case but also through N-type in the latter (Hegarty et al, 1997, Brosenitsch and Katz, 2001, Zhao et al, 2007. Of note, in SGNs, L-type calcium channels are required for survival signaling by chronic depolarization in vitro and by electrical stimulation via an implanted electrode in vivo (Han et al, 1994, Hegarty et al, 1997, Miller et al, 2003.…”