Enhancement of the Ca2(+)-current by a serum factor in cultured dorsal root ganglia neurons of the adult guinea pig.

To investigate effects of serum factor on the Ca2(+)-spike and neurite outgrowth in cultured nerve cells, dorsal root ganglia (DRG) neurons of the adult guinea pig were cultured in a serum-free N1 medium (N1 group) and a serum-containing medium (FCS group). The maximum rate of rise (MRR) of the Ca2(+)-spike, an indicator of the maximum Ca2(+)-current, was enhanced in the FCS group on day 5 in culture. The MRR of Ca2(+)-spike remained at a low level in the N1 group (2-10 days), but neurites outgrew rapidly during 2-5 days in both the FCS and N1 groups. Replacement of a serum-free medium by a serum-containing one on day 5 caused faster increase in the MRR of the Ca2(+)-spike. The active serum component for the Ca2(+)-spike enhancement was a heat-stable, small molecule. Chronic application of dibutyryl cyclic AMP (10 microM) mimicked the serum action on the Ca2(+)-spike. Whole-cell voltage-clamp experiment by a patch electrode showed that currents through the L- and T-type Ca-channels were enhanced in FCS group. Since kinetic and voltage-dependent gating properties of Ca-channels were similar between the FCS and N1 groups, available channel density might be increased by a serum factor.