Characterization of the type of calcium channel primarily regulating GABA exocytosis from brain nerve endings.
In an attempt to further characterize the type of Ca2+ channels primarily regulating GABA exocytosis, the effects of increasing concentrations of omega CTx MVIIC,-omega-Aga IVA and other Ca2+ channel blockers (nitrendipine, Cd2+ and Ni2+), commonly used for pharmacologically discerning among the various types of Ca2+ channels, were tested on the dissected Ca2+ dependent fraction of the depolarization evoked release of GABA from mouse brain synaptosomes. Our results show that omega-CTx MVIIC inhibits GABA exocytosis with a calculated IC50 of 3 microM and omega-Aga IVA with a calculated IC50 of 50 nM. The divalent cation Cd2+ only diminishes GABA exocytosis at 70 microM, but does not modify this response at lower concentrations (i.e. 1 and 10 microM). Neither nitrendipine (10 microM) nor Ni2+ (100 microM and 500 microM) modified GABA exocytosis. The failure of nitrendipine at a high concentration to inhibit GABA exocytosis discards L-type Ca2+ channels as the main regulators of this response; likewise that of Ni2+ discards Ca2+ channels of the N-type, and the failure of nM concentrations of omega-CTx MVIIC or 500 microM Ni2+, also discards alpha 1A/Q-type Ca2+ channels as the main regulators of the GABA response. On the basis of these results and in particular of the higher potency of omega-Aga IVA than omega-CTx MVIIC, it is concluded that the type of Ca2+ channels that primarily determine the exocytosis of GABA belong to a P-like type of Ca2+ channels.
Sitges
M
M
Instituto de Investigaciones Biomédicas, Depto. de Biología Molecular, UNAM, México, D.F.
Chiu
L M
LM
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D002104:Cadmium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051379:Mice; D008978:Mollusk Venoms / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D009568:Nitrendipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000502:physiology*; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D008978:Mollusk Venoms; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; D002104:Cadmium; C075851:omega-conotoxin-MVIIC; D005680:gamma-Aminobutyric Acid; C038806:1,4-dihydropyridine; D009532:Nickel; D009568:Nitrendipine