Functional properties of the purified N-type Ca2+ channel from rabbit brain.
N-type Ca2+ channels control a variety of key neuronal functions including transmitter release at synaptic terminals. The purified omega-conotoxin receptor from rabbit brain is a multisubunit complex composed of alpha 1B, alpha 2 delta, beta 3, and 95-kDa subunits. Immunoadsorption experiments confirm that the purified preparation does not contain alpha 1 subunits other than the omega-conotoxin-sensitive class B isoform. The functional properties of the purified channel have been analyzed further in lipid bilayers, and similarities to or differences from the native N-type Ca2+ channel have been outlined. Conserved properties include ion selectivity, open-time duration, and pharmacology (insensitivity to drugs affecting skeletal muscle L-type Ca2+ channels). Observed properties of the reconstituted channel which differ from the native channel include (a) sustained channel activity without Ca(2+)- or voltage-induced inactivation; (b) examples of extremely high open-state probability; (c) the absence of "run-down"; and (d) voltage independence of the Ca2+ channel gating. In addition, the conductance of the purified receptor is comprised between 7 and 27 picosiemens. Our results suggest that cellular components may play critical roles in the regulation of several biophysical properties and neuronal function of the native N-type Ca2+ channel.
De Waard
M
M
Howard Hughes Medical Institute, Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City 52242.
Witcher
D R
DR
Campbell
K P
KP
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D007700:Kinetics; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008564:Membrane Potentials; D009474:Neurons / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D011817:Rabbits; D015222:Sodium Channels / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology*; D013997:Time Factors; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D010455:Peptides; D015222:Sodium Channels; C053157:omega-conotoxin receptor; D001464:Barium; D020866:omega-Conotoxin GVIA