Pharmacological characterisation of voltage-sensitive calcium channels and neurotransmitter release from mouse cerebellar granule cells in culture.
Using subtype-specific Ca-channel blockers, we have characterised the voltage-sensitive Ca2+ currents as well as neurotransmitter release from cultured mouse cerebellar granule cells. The whole cell version of the patch clamp technique was adapted to monitor the isolated Ca-channel currents. The currents were activated at potentials more positive than -40 mV and were composed of at least four pharmacological distinct components being sensitive to nifedipine (35%), omega-conotoxin GVIA (10%), and omega-agatoxin IVA (42%) corresponding to L-, N-, and P-channel-mediated currents. The insensitive fraction (13%) possibly represented R channels. High potassium-evoked release of 3H-D-aspartate was used as a model of synaptic release. These studies were performed at relatively mild stimulation conditions (30 mM K+, 0.4 mM Ca2+), and 85% of the evoked release was Ca2+ dependent as well as tetrodotoxin and Cd2+ sensitive. Nifedipine and omega-agatoxin IVA dose dependently (IC50 values of 10 nM and 0.7 nM, respectively) blocked most of the release, whereas omega-conotoxin MVIIA (IC50 = 5 nM) caused partial blockage. The results indicate that several subtypes of voltage-sensitive Ca channels are present in mouse cerebellar granule cells. Furthermore, the data suggest that L, N, and P channels act in concert in the neurotransmitter release process.
Varming
T
T
NeuroSearch A/S, Glostrup, Denmark. tv@neurosearch.dk
Christopherson
P
P
Schousboe
A
A
Drejer
J
J
D000818:Animals; D001224:Aspartic Acid / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002531:Cerebellum / Q000166:cytology; D004305:Dose-Response Relationship, Drug; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D009474:Neurons / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011247:Pregnancy; D013111:Spider Venoms / Q000494:pharmacology; D014316:Tritium; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; D014316:Tritium; D001224:Aspartic Acid; D018698:Glutamic Acid; C078452:ziconotide; D020866:omega-Conotoxin GVIA; D009543:Nifedipine