Reevaluation of Ca2+ channel types and their modulation in bullfrog sympathetic neurons.
With 90 mM Ba2+, the main Ca2+ current in frog sympathetic neurons peaks near +30 mV and is blocked by omega-conotoxin GVIA (omega-CgTx). It is modulated by norepinephrine (NE) in a voltage-dependent manner via a membrane-delimited mechanism. Surprisingly, a different current dominates at more negative voltages (-30 to +10 mV). That novel current is not sensitive to selective blockers of L- or N-type channels (respectively, dihydropyridines or omega-CgTx) and is inhibited weakly if at all by NE. It is selectively inactivated at -40 mV and is selectively blocked by Ni2+, whereas Cd2+ is slightly more potent against the main current. The novel current is associated with a 19 pS channel (0.6 pA at 0 mV). This channel may have been misidentified as the single-channel correlate of the whole-cell N-type Ca2+ current in some previous studies.
Elmslie
K S
KS
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106.
Kammermeier
P J
PJ
Jones
S W
SW
D000818:Animals; D001464:Barium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology; D004553:Electric Conductivity; D005728:Ganglia, Sympathetic / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D011892:Rana catesbeiana; D020866:omega-Conotoxin GVIA
D015220:Calcium Channels; D004095:Dihydropyridines; D010455:Peptides; D001464:Barium; C038806:1,4-dihydropyridine; D020866:omega-Conotoxin GVIA; D009638:Norepinephrine