D-600 blocks open Ca2+ channels more profoundly than closed ones.
The open channel blocking action of the Ca2+ antagonists, D-600 and Cd2+, was investigated in single neurons isolated by enzymatic treatment from dorsal root ganglia of frog. Using a 'concentration clamp' (jump) technique Ca2+ antagonists were applied to the preparation just before (less than 100 ms) or during a depolarizing step which induced the maximal peak amplitude of Ca2+ current (ICa). The inhibitory action of D-600 was more pronounced when applied during a depolarizing step than when applied just before a depolarizing step. In contrast, Cd2+ was equally inhibitory, whether applied before or during the depolarization. Thus, D-600 affects open channels more quickly or more profoundly than closed ones, while Cd2+ acts equally on both open and closed Ca2+ channels.
D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D005711:Gallopamil / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials; D009475:Neurons, Afferent / Q000187:drug effects
D007473:Ion Channels; D002104:Cadmium; D005711:Gallopamil; D002118:Calcium