Nerve growth factor affects Ca²⁺ currents via the p75 receptor to enhance prolactin mRNA levels in GH₃ rat pituitary cells

Abstract

In clonal pituitary GH 3 cells, spontaneous action potentials drive the opening of Ca v 1 (L-type) channels, leading to Ca 2+ transients that are coupled to prolactin gene transcription. Nerve growth factor (NGF) has been shown to stimulate prolactin synthesis by GH 3 cells, but the underlying mechanisms are unknown. Here we studied whether NGF influences prolactin gene expression and Ca 2+ currents. By using RT-PCR, NGF (50 ng ml −1 ) was found to augment prolactin mRNA levels by ∼80% when applied to GH 3 cells for 3 days. A parallel change in the prolactin content was detected by Western blotting. Both NGF-induced responses were mimicked by an agonist (Bay K 8644) and prevented by a blocker (nimodipine) of L-type channels. In whole-cell patch-clamp experiments, NGF enhanced the L-type Ca 2+ current by ∼2-fold within 60 min. This effect reversed quickly upon growth factor withdrawal, but was maintained for days in the continued presence of NGF. In addition, chronic treatment (≥ 24 h) with NGF amplified the T-type current, which flows through Ca v 3 channels and is thought to support pacemaking activity. Thus, NGF probably increases the amount of Ca 2+ that enters per action potential and may also induce a late increase in spike frequency. MC192, a specific antibody for the p75 neurotrophin receptor, but not tyrosine kinase inhibitors (K252a and lavendustin A), blocked the effects of NGF on Ca 2+ currents. Overall, the results indicate that NGF activates the p75 receptor to cause a prolonged increase in Ca 2+ influx through L-type channels, which in turn up-regulates the prolactin mRNA.

Up-regulation of High Voltage-activated Ca2+ Channels in GC Somatotropes After Long-term Exposure to Ghrelin and Growth Hormone Releasing Peptide-6

“…Hence, it has been reported that chronic treatment with agonists of the dopaminergic D2 receptors down-regulate HVA Ca 2+ channel expression, leading to a reduction in Ca 2+ current and secretory activity in cultured melanotropes (Cota and Hiriart 1989;Chronwall et al 1995;Fass et al 1999). On the other hand, chronic treatment with epidermal growth factor has been shown either to increase (Meza et al 1994), or decrease (Fu et al 1997) HVA Ca 2+ current density, while nerve growth factor (Lopez- Dominguez et al 2006) or glucocorticoid hormones (Fomina et al 1993(Fomina et al , 1996 significantly enhance HVA current density in clonal pituitary cells.…”

Effects of nerve growth factor on the organotypic hippocampal slice culture using MEA system

“…When OHCs were treated with NGF together with k252a, NGF-induced neuronal activity increment still occurred, but the sustained LTP-like effect after wash-out no longer occurred. Previously, k252a was reported to suppressed LTP induction and synaptic activity [15,16]. Our results demonstrate that k252a may block the NGF-mediated LTP-like effect.…”

Regulation of CaV3.1 Channels by Glucocorticoids

“…Likewise, it is well established that the expression levels of LVA channels can be subjected to long-term regulation by different extracellular chemical messengers, including 17b-oestradiol, insulin, neural growth factor, transforming growth factor-b1, and bone morphogenetic protein-2 (Ritchie 1993;Meza et al 1994;Avila et al 2006;López-Domínguez et al 2006). Of particular interest is that chronic treatment with GCs decreases LVA current density in GH 3 cells (Meza et al 1994).…”