Cadmium block of calcium current in frog sympathetic neurons.
Cd2+ blocks whole-cell calcium currents in frog sympathetic neurons by 50% at approximately 300 nM. Strong depolarizations rapidly reverse that blockade (tau = 1.3 ms at +120 mV). Reblocking follows bimolecular kinetics (rate = 1.2 x 10(8) M-1 s-1) at voltages where channels are mostly open (0 to +30 mV). The unblocking rate is approximately 50 s-1, so the dissociation constant calculated from the rate constants is approximately 400 nM. Steady-state block is strong at -80 mV, so closed channels can also be blocked. However, reblocking is extremely slow (tau = 1-2 s) at voltages where the channels are mostly closed. The rates for Cd2+ entry and exit are greater than 100-fold lower for closed channels than for open channels, and closed channels appear to be closed at both ends.
Thévenod
F
F
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106.
Jones
S W
SW
D000818:Animals; D001001:Anura; D055592:Biophysical Phenomena; D001703:Biophysics; D002104:Cadmium / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D005728:Ganglia, Sympathetic / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism
D015220:Calcium Channels; D002104:Cadmium