Nerve growth factor affects Ca super(2+) currents via the p75 receptor to enhance prolactin mRNA levels in GH sub(3) rat pituitary cells

• Published in: The Journal of physiology Vol. 574; no. 2; pp. 349 - 365
• Main Authors: Lopez-Dominguez, Adriana M, Espinosa, Juan Luis, Navarrete, Araceli, Avila, Guillermo, Cota, Gabriel
• Format: Journal Article
• Language: English
• Published: 01.07.2006
• ISSN: 0022-3751; 1469-7793

In clonal pituitary GH sub(3) cells, spontaneous action potentials drive the opening of Ca sub(v)1 (L-type) channels, leading to Ca super(2+) transients that are coupled to prolactin gene transcription. Nerve growth factor (NGF) has been shown to stimulate prolactin synthesis by GH sub(3) cells, but the underlying mechanisms are unknown. Here we studied whether NGF influences prolactin gene expression and Ca super(2+) currents. By using RT-PCR, NGF (50 ng ml super(-1)) was found to augment prolactin mRNA levels by similar to 80% when applied to GH sub(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 super(2+) current by similar to 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 ( greater than or equal to 24 h) with NGF amplified the T-type current, which flows through Ca sub(v)3 channels and is thought to support pacemaking activity. Thus, NGF probably increases the amount of Ca super(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 super(2+) currents. Overall, the results indicate that NGF activates the p75 receptor to cause a prolonged increase in Ca super(2+) influx through L-type channels, which in turn up-regulates the prolactin mRNA.