Direct Observation of a Preinactivated, Open State in BK Channels with beta2 Subunits Export

@article{citeulike:486657, abstract = {Proteins arising from the Slo family assemble into homotetramers to form functional large-conductance, Ca2+- and voltage-activated K+ channels, or BK channels. These channels are also found in association with accessory {beta} subunits, which modulate several aspects of channel gating and expression. Coexpression with either of two such subunits, {beta}2 or {beta}3b, confers time-dependent inactivation onto BK currents. mSlo1+{beta}3b channels display inactivation that is very rapid but incomplete. Previous studies involving macroscopic recordings from these channels have argued for the existence of a second, short-lived conducting state in rapid equilibrium with the nonconducting, inactivated conformation. This state has been termed "pre-inactivated," or O*. {beta}2-mediated inactivation, in contrast, occurs more slowly but is virtually complete at steady state. Here we demonstrate, using both macroscopic and single channel current recordings, that a preinactivated state is also a property of mSlo1+{beta}2 channels. Detection of this state is enhanced by a mutation (W4E) within the initial {beta}2 NH2-terminal segment critical for inactivation. This mutation increases the rate of recovery to the preinactivated open state, yielding macroscopic inactivation properties qualitatively more similar to those of {beta}3b. Furthermore, short-lived openings corresponding to entry into the preinactivated state can be observed directly with single-channel recording. By examining the initial openings after depolarization of a channel containing {beta}2-W4E, we show that channels can arrive directly at the preinactivated state without passing through the usual long-lived open conformation. This final result suggests that channel opening and inactivation are at least partly separable in this channel. Mechanistically, the preinactivated and inactivated conformations may correspond to binding of the {beta} subunit NH2 terminus in the vicinity of the cytoplasmic pore mouth, followed by definitive movement of the NH2 terminus into a position of occlusion within the ion-conducting pathway.}, author = {Benzinger, Richard G. and Xia, Xiao-Ming and Lingle, Christopher J.}, citeulike-article-id = {486657}, citeulike-linkout-0 = {http://dx.doi.org/10.1085/jgp.200509425}, citeulike-linkout-1 = {http://www.jgp.org/cgi/content/abstract/127/2/119}, citeulike-linkout-2 = {http://view.ncbi.nlm.nih.gov/pubmed/16418401}, citeulike-linkout-3 = {http://www.hubmed.org/display.cgi?uids=16418401}, day = {30}, doi = {10.1085/jgp.200509425}, journal = {J. Gen. Physiol.}, keywords = {beta, bk, channel, subunit}, month = {January}, number = {2}, pages = {119--131}, posted-at = {2006-01-31 02:20:10}, priority = {3}, title = {Direct Observation of a Preinactivated, Open State in BK Channels with {beta}2 Subunits}, url = {http://dx.doi.org/10.1085/jgp.200509425}, volume = {127}, year = {2006} }

TY - JOUR ID - citeulike:486657 L3 - citeulike-article-id:486657 N2 - Proteins arising from the Slo family assemble into homotetramers to form functional large-conductance, Ca2+- and voltage-activated K+ channels, or BK channels. These channels are also found in association with accessory {beta} subunits, which modulate several aspects of channel gating and expression. Coexpression with either of two such subunits, {beta}2 or {beta}3b, confers time-dependent inactivation onto BK currents. mSlo1+{beta}3b channels display inactivation that is very rapid but incomplete. Previous studies involving macroscopic recordings from these channels have argued for the existence of a second, short-lived conducting state in rapid equilibrium with the nonconducting, inactivated conformation. This state has been termed "pre-inactivated," or O*. {beta}2-mediated inactivation, in contrast, occurs more slowly but is virtually complete at steady state. Here we demonstrate, using both macroscopic and single channel current recordings, that a preinactivated state is also a property of mSlo1+{beta}2 channels. Detection of this state is enhanced by a mutation (W4E) within the initial {beta}2 NH2-terminal segment critical for inactivation. This mutation increases the rate of recovery to the preinactivated open state, yielding macroscopic inactivation properties qualitatively more similar to those of {beta}3b. Furthermore, short-lived openings corresponding to entry into the preinactivated state can be observed directly with single-channel recording. By examining the initial openings after depolarization of a channel containing {beta}2-W4E, we show that channels can arrive directly at the preinactivated state without passing through the usual long-lived open conformation. This final result suggests that channel opening and inactivation are at least partly separable in this channel. Mechanistically, the preinactivated and inactivated conformations may correspond to binding of the {beta} subunit NH2 terminus in the vicinity of the cytoplasmic pore mouth, followed by definitive movement of the NH2 terminus into a position of occlusion within the ion-conducting pathway. IS - 2 JF - J. Gen. Physiol. EP - 131 TI - Direct Observation of a Preinactivated, Open State in BK Channels with {beta}2 Subunits VL - 127 SP - 119 KW - beta KW - bk KW - channel KW - subunit AU - Benzinger, Richard AU - Xia, Xiao-Ming AU - Lingle, Christopher PY - 2006/01/30/ UR - http://dx.doi.org/10.1085/jgp.200509425 ER -