The development and pharmacological characterization of calcium channel currents in cultured embryonic rat septal cells

We characterized the development and pharmacology of Ca2+ channel currents in NGF-treated embryonic day 21 cultured rat septal cells. Using standard w hole-cell voltage clamp techniques, cells were held at -80 mV and depolariz ed to construct current-voltage relations in conditions that eliminated Na or K+ currents. Barium (10 mM) was used as the charge carrier. Maximum cur rent was produced when cells were depolarized to 0 or +10 mV. Recordings fr om 77 cells revealed that Ca2+ channel current density increases over time in culture from nearly 0 pA/pF on day 2 in vitro (0.65 +/- 0.65 pA/pF) to ( 6.95 +/- 1.59 pA/pF) on days 6-8. This was followed by a period where curre nts became nearly 3 limes more dense (21.05 +/- 7.16 pA/pF) at days 9-17. T here was Little or no evidence for low voltage activated currents, Bath app lication of 50-100 mu M CdCl2 abolished similar to 95% of the current. Appl ication of 10 mu M nimodipine produced a 50.5 +/- 3.22% reduction in curren t, 2 mu M omega-CTx-GVIA produced a 32.4 +/- 7.3% reduction, and applicatio n of 4 mu M omega-Aga-IVA produced a 29.5 +/- 5.73% reduction in current. W hen all three inhibitors (10 mu M nimodipine, 2 mu M omega-CTx-GVIA, and 4 mu M omega-Aga-IVA) were applied simultaneously, a residual current remaine d that was 18.0 +/- 4.9% of the total current and was completely abolished by application of CdCl2. This is the first report to characterize Ca2+ chan nel currents in cultured embryonic septal cells. These data indicate that t here is a steady increase in Ca2+ channel expression over time in vitro, an d show that like other cultured neuronal cells, septal cells express multip le Ca2+ channel types including L, N, P/Q and R-type channels. (C) 1999 Els evier Science B.V. All rights reserved.