L-type calcium channel activation up-regulates the mRNAs for two different sodium channel α subunits (Nav1.2 and Nav1.3) in rat pituitary GH3 cells

Calcium entry through L-type Ca2+ channels has been shown to increase the number of Na+ channels in GH(3) cells, a clonal line of rat pituitary cells. To test whether this Ca2+ influx affects the levels of Na+ channel mRNAs, we first examined which Na+ channel subunits are expressed in GH(3) cells. By using RT-PCR with specific primers, we detected transcripts for four a subunits (Na(v)1.1, Na(v)1.2, Na(v)1.3 and Na(v)1.6) and two auxiliary subunits (beta1 and beta3) of Na+ channels in total RNA from control GH(3) cells. Next, we optimized the RT-PCR conditions to allow detection of cDNAs in the linear range of the assay. These conditions were then used to assess the transcript levels of Na+ channels after chronic exposure (72 h) of GH(3) cells to the L-type Ca2+ channel blocker nimodipine (1 muM) or the L-type channel agonist Bay K 8644 (0.5 muM). Nimodipine treatment caused a moderate reduction (similar to30%) of the mRNA for Na(v)1.2 and a marked reduction (similar to70%) of the mRNA for Na(v)1.3, whereas treatment with Bay K 8644 produced 90-130% increases in these same mRNAs. There were no concomitant changes in the mRNAs for Na(v)1.1 and Na(v)1.6. Moreover, beta1 and beta3 mRNA levels were also unchanged. Thus, GH(3) cells express multiple Na+ channel subunits and L-type Ca2+ channel activity up-regulates in a specific way the mRNAs for Na(v)1.2 and Na(v)1.3. These findings improve our knowledge on the molecular diversity of Na+ channels in pituitary cells and extend the actual view about the regulation of Na+ channel gene expression by Ca2+ influx. (C) 2003 Elsevier B.V. All rights reserved.