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Ca 2+ influx through both L‐ and N‐type Ca 2+ channels increases c‐ fos expression by electrical stimulation of sympathetic neurons
Author(s) -
Zhao Rubing,
Liu Liwang,
Rittenhouse Ann R.
Publication year - 2007
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.2007.05359.x
Subject(s) - depolarization , creb , stimulation , c fos , medicine , endocrinology , superior cervical ganglion , chemistry , premovement neuronal activity , immediate early gene , gene expression , neuroscience , transcription factor , biology , gene , biochemistry
During direct membrane depolarization, Ca 2+ influx primarily through L‐type Ca 2+ (L‐) channels initiates activity‐dependent gene transcription. This is surprising given that in most neurons a minority of the total Ca 2+ current arises from L‐channel activity. However, many studies have stimulated Ca 2+ influx with unphysiological stimuli such as chronic membrane depolarization using high K + medium. Few studies have tested whether other Ca 2+ channels stimulate gene transcription in adult neurons as a consequence of direct electrical stimulation. Therefore, we evaluated the role of L‐ and N‐type Ca 2+ (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 Ca 2+ 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 Ca 2+ 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.