Comparison of binding affinities of omega-conotoxin and amlodipine to N-type Ca2+ channels in rat brain.
OBJECTIVE
To compare the binding affinities of omega-conotoxin (CTX) and amlodipine to N-type Ca2+ channels in rat brains.


METHODS
Whole rat brains were homogenized in HEPES buffer 50 mmol.L-1 (pH 7.4) and centrifuged at 40,000 x g to obtain the membrane-entriched fraction. 125I-omega-conotoxin (125I-omega-CTX) was used as a radioligand. Using radioligand binding assay Kd and Bmax values of the radioligand were determined by Scatchard analysis. The IC50 value for each drug was obtained from displacement experiments.


RESULTS
No differences in Bmax values of 125I-omega-CTX binding sites between frozen and fresh tissues were observed. Values of Kd and Bmax of N-type Ca2+ channels were 0.02 +/- 0.01 nmol.L-1 and 1029 +/- 108 pmol/g protein, respectively. The pKi values of omega-CTX and amlodipine were 9.57 and less than 4, respectively. The pKi values of propranolol, prazosin, atropine, and histamine were very low.


CONCLUSIONS
The binding affinity of the L-type Ca(2+)-antagonist amlodipine to N-type Ca2+ channels in the rat brain was very low.
Qu
Y L
YL
Department of Pharmacology, Niigata College of Pharmacy, Japan.
Sugiyama
K
K
Ohnuki
T
T
Hattori
K
K
Watanabe
K
K
Nagatomo
T
T
D017311:Amlodipine / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D008297:Male; D010455:Peptides / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D017311:Amlodipine; D020866:omega-Conotoxin GVIA