Expression of voltage-dependent calcium channels in the embryonic rat midbrain.
The diversity of expression of high-voltage activated voltage-dependent calcium channels (VDCC) was investigated with whole-cell voltage-clamp recordings from dissociated embryonic rat ventral mesencephalic cells over a 7-day culture period. Cell phenotype was identified post-recording by fluorescent immunocytochemistry as tyrosine hydroxylase positive (TH+) or glutamic acid decarboxylase positive (GAD+). Both TH+ and GAD+ cells displayed high-threshold calcium (Ca(2+)) currents activated by depolarisations positive to -60 mV. In both cell types, pharmacological dissection using selective VDCC inhibitors, omega-agatoxin IVA (Aga IVA), omega-conotoxin GVIA (GVIA) and nifedipine demonstrated the existence of P/Q-, N- and L-type VDCC, respectively. The remaining residual current could be blocked by cadmium. It was found that the contribution to the whole-cell current by the N-type channel was greater in TH+ cells than GAD+ cells at each time point examined, whilst the contribution to the whole-cell current by the L-type channel was greater in GAD+ cells than TH+ cells. However, over the 7-day culture period, the expression of VDCC types in both cell phenotypes changed in a similar fashion, with the contribution to the whole-cell current from the N-type current decreasing, and the contribution from the R-type current increasing. Our data could provide new insights into a range of neurodevelopmental mechanisms related to Ca(2+) homeostasis in developing mesencephalic neurons.
Whyte
Kathryn A
KA
Department of Pharmacology, Mansfield Road, Oxford OX1 3QT, UK.
Greenfield
Susan A
SA
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D005333:Fetus; D005968:Glutamate Decarboxylase / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008636:Mesencephalon / Q000166:cytology / Q000196:embryology* / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010641:Phenotype; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D014446:Tyrosine 3-Monooxygenase; D005968:Glutamate Decarboxylase; D002118:Calcium