FUNCTIONAL-PROPERTIES OF THE PURIFIED N-TYPE CA2+ CHANNEL FROM RABBITBRAIN

N-type Ca2+ channels control a variety of key neuronal functions inclu ding transmitter release at synaptic terminals. The purified omega-con otoxin receptor from rabbit brain is a multisubunit complex composed o f alpha(1B), alpha 2 delta, beta 3, and 95-kDa subunits. Immunoadsorpt ion experiments confirm that the purified preparation does not contain cn, 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 th e native N-type Ca2+ channel have been outlined. Conserved properties include ion selectivity, open-time duration, and pharmacology (insensi tivity to drugs affecting skeletal muscle L-type Ca2+ channels). Obser ved properties of the reconstituted channel which differ from the nati ve channel include (a) sustained channel activity without Ca2+- or vol tage-induced inactivation; (b) examples of extremely high open-state p robability; (c) the absence of ''run-down''; and (d) voltage independe nce of the Ca2+ channel gating. In addition, the conductance of the pu rified receptor is comprised between 7 and 27 picosiemens. Our results suggest that cellular components may play critical roles in the regul ation of several biophysical properties and neuronal function of the n ative N-type Ca2+ channel,