Multiple components of Ca2+ channel facilitation in cerebellar granule cells: expression of facilitation during development in culture.
The contribution of pharmacologically distinct Ca2+ channels to prepulse-induced facilitation was studied in mouse cerebellar granule cells. Ca2+ channel facilitation was measured as the percentage increase in the whole-cell current recorded during a test pulse before and after it was paired with a positive prepulse. The amount of facilitation was small in recordings made during the first few days in tissue culture but increased substantially after 1 week. L-type channels accounted for the largest proportion of facilitation in 1-week-old cells (60-70%), whereas N-type channels contributed very little (approximately 3%). The toxins omega-agatoxin IVa or omega-conotoxin MVIIC (after block of N-, L-, and P-type channels) each blocked a small percentage of facilitation (approximately 12 and 14%, respectively). Perfusion of cells with GTP-gamma-S enhanced the facilitation of N-type channels, whereas it inhibited of L-type channels. During development in vitro, the contribution of L-type channels to the whole-cell current decreased. Single-channel recordings showed the presence of 10 and 15 pS L-type Ca2+ channels in 1-d-old cells. After 1 week in culture, a approximately 25 pS L-type channel dominated recordings from cell-attached patches. Positive prepulses increased the activity of the 25 pS channel but not of the smaller conductance channels. The expression of Ca(2+) channel facilitation during development may contribute to changes in excitability that allow frequency-dependent Ca(2+) influx during the period of active synaptogenesis
Parri
H R
HR
Department of Cellular and Molecular Pharmacology, School of Medicine, University of California, San Francisco 94143-0450, USA.
Lansman
J B
JB
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D016922:Cellular Senescence; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D004095:Dihydropyridines / Q000819:agonists; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000502:physiology*; D010766:Phosphorylation
D015220:Calcium Channels; D004095:Dihydropyridines; D016244:Guanosine 5'-O-(3-Thiotriphosphate)