Healthcare Provider Characteristics and Cardiopulmonary Resuscitation Quality During Infant Resuscitation: A Simulation Study

INTRODUCTION

Healthcare providers' anthropometric characteristics can adversely affect adult cardiopulmonary resuscitation (CPR) performance quality. However, their effects on infant CPR are unknown. We aimed to determine any relationships between healthcare provider characteristics (anthropomorphic, demographics, training, occupational data) and simulated infant CPR performance at multiple international sites. Our secondary aim was to examine provider's CPR performance degradation.

METHODS

Providers from 4 international hospitals performed 2 minutes of single-rescuer simulated infant CPR using 2015 American Heart Association Basic Life Support criteria with guidance from a real-time visual performance feedback device. Providers' characteristics were collected, and the simulator collected compression and ventilation data. Multivariate analyses examined the entire 2 minutes and performance degradation.

RESULTS

Data from 127 participants were analyzed. Although median values for all compression variables (depth, rate, lean) and ventilation volume were within guideline target ranges, when looking at individuals, only 52% chest compressions and 20% ventilations adhered to the American Heart Association guidelines. Age was found to be independently associated with ventilation volume (direct-relationship), and height was associated with chest compression lean (shorter participant-deeper lean). No significant differences were noted based on sex or body mass index. Neonatal intensive care unit participants were noted to perform shallower chest compressions (P < 0.001). Overall, there was minimal evidence of performance degradation over 2 minutes.

CONCLUSIONS

Isolated provider characteristics were noted among a diverse cohort of healthcare providers that may affect the CPR quality on a simulated infant. Understanding the relationships between provider characteristics and CPR quality could inform future infant CPR guidelines customized for the provider and not just the patient.

A systems analysis of the COVID-19 pandemic response in the United Kingdom - Part 1 - The overall context

The most common reaction to suggesting that we could learn valuable lessons from the way the current pandemic has been/ is being handled, is to discourage the attempt; as it is suggested that it can all be done more accurately and authoritatively after the inevitable Public Inquiry (Slater, 2019). On the other hand, a more constructive approach, is to capture and understand the work that was actually done.This would include normal activities, as well as positive adaptations to challenges and failures that may have occurred. Such an approach aimed at improving what worked, rather than blaming people for what went wrong, has the potential to contribute more successfully to controlling the consequences of the current crisis. Such an approach should thus be aimed at detecting and feeding back lessons from emerging and probably unexpected behaviours and helping to design the system to adapt better to counter the effects. The science and discipline of Human Factors (HF) promotes system resilience. This can be defined as an organisation's ability to adjust its functioning before, during or after significant disturbances (such as a pandemic), enabling adaptation and operation under both anticipated and unanticipated circumstances. A "functional" approach methodology enables the identification of where the system and its various interdependent functions (an activity or set of activities that are required to give a certain output), could be improved and strengthened; if not immediately, at least for the future. Along these lines, suggestions for adding key resilience functions are additionally identified and outlined. The application and insights gained from this functional approach to the 2015 MERS-Cov pandemic in South Korea has been seen as contributing substantially to the effective response to the current crisis in that country (Min, submitted for publication). In this paper, we present an overarching framework for a series of projects that are planned to carry out focussed systems-based analysis to generate learning from key aspects of the COVID-19 pandemic response in the United Kingdom.

The use of virtual reality and augmented reality to enhance cardio-pulmonary resuscitation: a scoping review

BACKGROUND AND OBJECTIVE

Virtual reality (VR) and augmented reality (AR) have been proposed as novel methods to enhance cardio-pulmonary resuscitation (CPR) performance and increase engagement with CPR training. A scoping review was conducted to map the global evolution of these new approaches to CPR training, to assess their efficacy and determine future directions to meet gaps in current knowledge.

METHODS

A standardised five-stage scoping methodology was used to (1) identify the research question, (2) identify relevant studies, (3) select the studies, (4) chart the data and (5) summarise the findings. The Kirkpatrick model levels of evidence were used to chart and assess the efficacy of each intervention reported. A multi-pronged search term strategy was used to search the Web of Science, PubMed, CINAHL and EMBASE databases up to June 2020.

RESULTS

A total of 42 articles were included in this review. The first relevant paper identified was published in 2009 and based on VR, from 2014 onwards there was a large increase in the volume of work being published regarding VR and AR uses in CPR training. This review reports Kirkpatrick level one to three evidence for the use of VR/AR-CPR. Inconsistencies in the specific language, keywords used and methodologies are highlighted.

CONCLUSION

VR and AR technologies have shown great potential in the area of CPR, and there is continuing evidence of new novel applications and concepts. As VR/AR research into CPR reaches an inflection point, it is key to bring collaboration and consistency to the wider research community, to enable the growth of the area and ease of access to the wider medical community.

The effect of an International competitive leaderboard on self-motivated simulation-based CPR practice among healthcare professionals: A randomized control trial

BACKGROUND

Little is known about how best to motivate healthcare professionals to engage in frequent cardiopulmonary resuscitation (CPR) refresher skills practice. A competitive leaderboard for simulated CPR can encourage self-directed practice on a small scale. The study aimed to determine if a large-scale, multi-center leaderboard improved simulated CPR practice frequency and CPR performance among healthcare professionals.

METHODS

This was a multi-national, randomized cross-over study among 17 sites using a competitive online leaderboard to improve simulated practice frequency and CPR performance. All sites placed a Laerdal® ResusciAnne or ResusciBaby QCPR manikin in 1 or more clinical units - emergency department, ICU, etc. - in easy reach for 8 months. These simulators provide visual feedback during 2-minute compressions-only CPR and a performance score. Sites were randomly assigned to the intervention for the first 4-months or the second 4-months. Following any CPR practice by a healthcare professional, participants uploaded scores and an optional 'selfie' photo to the leaderboard. During the intervention phase, the leaderboard displayed ranked scores and high scores earned digital badges. The leaderboard did not display control phase participants. Outcomes included CPR practice frequency and mean compression score, using non-parametric statistics for analyses.

RESULTS

Nine-hundred nineteen participants completed 1850 simulated CPR episodes. Exposure to the leaderboard yielded 1.94 episodes per person compared to 2.14 during the control phase (p = 0.99). Mean CPR performance participants did not differ between phases: 90.7 vs. 89.3 (p = 0.19).

CONCLUSION

A competitive leaderboard was not associated with an increase in self-directed simulated CPR practice or improved performance.

Ten years of simulation-based training in pediatric anesthesia: The inception, evolution, and dissemination of the Managing Emergencies in Pediatric Anesthesia (MEPA) course

2016 marked the 10-year anniversary of the inception of the Managing Emergencies in Paediatric Anaesthesia (MEPA) course. This simulation-based program was originally created to allow trainees in pediatric anesthesia to experience operating room emergencies which although infrequent, would be considered key competencies for any practicing anesthetist with responsibility for providing care to children. Since its original manifestation, the course has evolved in content, scope, and worldwide availability, such that it is now available at over 60 locations on five continents. The content has been modified for different learner groups and translated into several languages. This article describes the history, evolution, and dissemination of the MEPA course to share lessons learnt with educators considering the launch of similar initiatives in their field.

Exploring Mechanisms for Effective Technology-Enhanced Simulation-based Education in Wilderness Medicine: A Systematic Review

BACKGROUND

 Technology-enhanced simulation is well-established in healthcare teaching curricula, including those regarding wilderness medicine. Compellingly, the evidence base for the value of this educational modality to improve learner competencies and patient outcomes are increasing.

AIMS

 The aim was to systematically review the characteristics of technology-enhanced simulation presented in the wilderness medicine literature to date. Then, the secondary aim was to explore how this technology has been used and if the use of this technology has been associated with improved learner or patient outcomes.

METHODS

 EMBASE and MEDLINE were systematically searched from 1946 to 2014, for articles on the provision of technology-enhanced simulation to teach wilderness medicine. Working independently, the team evaluated the information on the criteria of learners, setting, instructional design, content, and outcomes.

RESULTS

 From a pool of 37 articles, 11 publications were eligible for systematic review. The majority of learners in the included publications were medical students, settings included both indoors and outdoors, and the main focus clinical content was initial trauma management with some including leadership skills. The most prevalent instructional design components were clinical variation and cognitive interactivity, with learner satisfaction as the main outcome.

CONCLUSIONS

 The results confirm that the current provision of wilderness medicine utilizing technology-enhanced simulation is aligned with instructional design characteristics that have been used to achieve effective learning. Future research should aim to demonstrate the translation of learning into the clinical field to produce improved learner outcomes and create improved patient outcomes.

A review of undergraduate interprofessional simulation-based education (IPSE)

Interprofessional simulation-based education (IPSE) is becoming an increasingly popular educational strategy worldwide within undergraduate healthcare curricular. The purpose of the literature review was to examine qualitative, quantitative and mixed/multi-method research studies featuring undergraduate IPSE. A literature review was conducted using CINAHL, MEDLINE, and PsycINFO databases from January 1999 to September 2011 and pre-set criteria. The criteria used to screen all 120 abstracts included: (a) the article pertained to both simulation and undergraduate IPE and (b) the article reported a research study. Eighteen articles which met the pre-set criteria were included in the literature review. All studies featured outcome measures; many were purposely designed and lacked psychometric development and evaluation. Key IPSE drivers included capacity planning, preparedness for disaster management and improving patient care through the evaluation of teambuilding, teamwork skills or communicating within inter-disciplinary teams. Studies evaluated/explored either student or teacher perspectives of learning within the context of IPSE or both. The IPSE learning processes varied considerably in relation to duration, fidelity and professions involved. The scenarios ranged from managing adults admitted to hospital settings, mass casualty/mock disaster patient management to the use of training wards. The majority of the articles identified common IPSE outcomes relating to increased confidence, knowledge, leadership, teamwork, and communication skills. Based on the findings of this review, the authors suggest that further multi-site, longitudinal research studies are required to provide evidence of the transferability of skills developed during IPSE and their overall impact on both undergraduate education and healthcare.

Endotracheal DNase for atelectasis in ventilated neonates

Management of atelectasis and lung collapse in ventilated neonates remains a common challenge in the neonatal intensive care unit. Recombinant human DNase (rhDNase) is an established treatment of atelectasis in cystic fibrosis and its use is also reported in the management of asthma, respiratory syncitial virus bronchiolitis and bronchiectasis to liquefy sputum and aid its clearance from the lungs. We report the use of rhDNase in a subgroup of ventilated neonates with severe end-stage respiratory failure and atelectasis. Three of the four patients showed clinical improvement. A previously undiagnosed lung anomaly was subsequently identified in the fourth patient. Future randomized studies could examine any potential benefits of this emerging therapy.

Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution

Ion transport proteins must remove an ion's hydration shell to coordinate the ion selectively on the basis of its size and charge. To discover how the K+ channel solves this fundamental aspect of ion conduction, we solved the structure of the KcsA K+ channel in complex with a monoclonal Fab antibody fragment at 2.0 A resolution. Here we show how the K+ channel displaces water molecules around an ion at its extracellular entryway, and how it holds a K+ ion in a square antiprism of water molecules in a cavity near its intracellular entryway. Carbonyl oxygen atoms within the selectivity filter form a very similar square antiprism around each K+ binding site, as if to mimic the waters of hydration. The selectivity filter changes its ion coordination structure in low K+ solutions. This structural change is crucial to the operation of the selectivity filter in the cellular context, where the K+ ion concentration near the selectivity filter varies in response to channel gating.

Energetic optimization of ion conduction rate by the K+ selectivity filter

The K+ selectivity filter catalyses the dehydration, transfer and rehydration of a K+ ion in about ten nanoseconds. This physical process is central to the production of electrical signals in biology. Here we show how nearly diffusion-limited rates are achieved, by analysing ion conduction and the corresponding crystallographic ion distribution in the selectivity filter of the KcsA K+ channel. Measurements with K+ and its slightly larger analogue, Rb+, lead us to conclude that the selectivity filter usually contains two K+ ions separated by one water molecule. The two ions move in a concerted fashion between two configurations, K+-water-K+-water (1,3 configuration) and water-K+-water-K+ (2,4 configuration), until a third ion enters, displacing the ion on the opposite side of the queue. For K+, the energy difference between the 1,3 and 2,4 configurations is close to zero, the condition of maximum conduction rate. The energetic balance between these configurations is a clear example of evolutionary optimization of protein function.

Potassium channel receptor site for the inactivation gate and quaternary amine inhibitors

Many voltage-dependent K+ channels open when the membrane is depolarized and then rapidly close by a process called inactivation. Neurons use inactivating K+ channels to modulate their firing frequency. In Shaker-type K+ channels, the inactivation gate, which is responsible for the closing of the channel, is formed by the channel's cytoplasmic amino terminus. Here we show that the central cavity and inner pore of the K+ channel form the receptor site for both the inactivation gate and small-molecule inhibitors. We propose that inactivation occurs by a sequential reaction in which the gate binds initially to the cytoplasmic channel surface and then enters the pore as an extended peptide. This mechanism accounts for the functional properties of K+ channel inactivation and indicates that the cavity may be the site of action for certain drugs that alter cation channel function.

Structure of the RCK domain from the E. coli K+ channel and demonstration of its presence in the human BK channel

The intracellular C-terminal domain structure of a six-transmembrane K+ channel from Escherichia coli has been solved by X-ray crystallography at 2.4 A resolution. The structure is representative of a broad class of domains/proteins that regulate the conductance of K+ (here referred to as RCK domains) in prokaryotic K+ transporters and K+ channels. The RCK domain has a Rossmann-fold topology with unique positions, not commonly conserved among Rossmann-fold proteins, composing a well-conserved salt bridge and a hydrophobic dimer interface. Structure-based amino acid sequence alignments and mutational analysis are used to demonstrate that an RCK domain is also present and is an important component of the gating machinery in eukaryotic large-conductance Ca2+ activated K+ channels.

Assessing the subjective experience of being a participant in psychiatric research

OBJECTIVE

To address both clinical and ethical concerns in psychiatric research, the study assessed the subjective experience of being a participant in a feasibility study of outcome in long-term psychodynamic psychotherapy and psychoanalysis.

METHOD

A questionnaire assessing positive and negative reactions to three typical research methodologies (self-report questionnaires, structured diagnostic interviews, and tape-recording of sessions) was administered to 23 patient-therapist pairs.

RESULTS

Patients reported that questionnaires and interviews were slightly to moderately helpful in promoting self-realization and facilitating therapy, and not at all to slightly intrusive and disruptive. Adjustment to audiotaping of sessions was rapid (within two sessions). Therapists significantly overestimated the negative effects and underestimated the positive benefit patients reported from participating in research.

CONCLUSIONS

Traditional objections to research in dynamic psychotherapy on the grounds that patients experience research procedures as significantly intrusive and disruptive appear to be unfounded.

Structure of the cytoplasmic beta subunit-T1 assembly of voltage-dependent K+ channels

The structure of the cytoplasmic assembly of voltage-dependent K+ channels was solved by x-ray crystallography at 2.1 angstrom resolution. The assembly includes the cytoplasmic (T1) domain of the integral membrane alpha subunit together with the oxidoreductase beta subunit in a fourfold symmetric T1(4)beta4 complex. An electrophysiological assay showed that this complex is oriented with four T1 domains facing the transmembrane pore and four beta subunits facing the cytoplasm. The transmembrane pore communicates with the cytoplasm through lateral, negatively charged openings above the T1(4)beta4 complex. The inactivation peptides of voltage-dependent K(+) channels reach their site of action by entering these openings.

Energetic and structural interactions between delta-dendrotoxin and a voltage-gated potassium channel

Dendrotoxin proteins isolated from Mamba snake venom block potassium channels with a high degree of specificity and selectivity. Using site-directed mutagenesis we have identified residues that constitute the functional interaction surfaces of delta-dendrotoxin and its voltage-gated potassium channel receptor. delta-Dendrotoxin uses a triangular patch formed by seven side-chains (Lys3, Tyr4, Lys6, Leu7, Pro8, Arg10, Lys26) to block K(+) currents carried by a Shaker potassium channel variant. The inhibitory surface of the toxin interacts with channel residues at Shaker positions 423, 425, 427, 431, and 449 near the pore. Amino acid mutations that interact across the toxin-channel interface were identified by mutant cycle analysis. These results constrain the possible orientation of dendrotoxin with respect to the K(+) channel structure. We propose that dendrotoxin binds near the pore entryway but does not act as a physical plug.

The cavity and pore helices in the KcsA K+ channel: electrostatic stabilization of monovalent cations

The electrostatic influence of the central cavity and pore alpha helices in the potassium ion channel from Streptomyces lividans (KcsA K+ channel) was analyzed by solving the finite difference Poisson equation. The cavity and helices overcome the destabilizing influence of the membrane and stabilize a cation at the membrane center. The electrostatic effect of the pore helices is large compared to that described for water-soluble proteins because of the low dielectric membrane environment. The combined contributions of the ion self-energy and the helix electrostatic field give rise to selectivity for monovalent cations in the water-filled cavity. Thus, the K+ channel uses simple electrostatic principles to solve the fundamental problem of ion destabilization by the cell membrane lipid bilayer.

Structure of a voltage-dependent K+ channel beta subunit

The integral membrane subunits of many voltage-dependent potassium channels are associated with an additional protein known as the beta subunit. One function of beta subunits is to modify K+ channel gating. We have determined the structure of the conserved core of mammalian beta subunits by X-ray crystallography at 2.8 A resolution. Like the integral membrane component of K+ channels, beta subunits form a four-fold symmetric structure. Each subunit is an oxidoreductase enzyme complete with a nicotinamide co-factor in its active site. Several structural features of the enzyme active site, including its location with respect to the four-fold axis, imply that it may interact directly or indirectly with the K+ channel's voltage sensor. This structure suggests a mechanism for coupling membrane electrical excitability directly to chemistry of the cell.

A snake toxin inhibitor of inward rectifier potassium channel ROMK1

Mamba snake dendrotoxins have been used extensively in biochemical and physiological studies of K+ channels of the brain. Their known targets of inhibition have been limited to the family of voltage-gated K+ channels. We report the isolation of a dendrotoxin inhibitor of ROMK1, a channel belonging to the inward rectifier family of K+ channels. The inhibitory activity, fractionated to purity with FPLC and HPLC, is identical to a previously identified delta-dendrotoxin. To verify that delta-dendrotoxin blocks ROMK1 channels, a cDNA encoding the toxin was synthesized and recombinant toxin expressed in Escherichia coli. Electrophysiological recordings reveal that recombinant delta-dendrotoxin has a half-maximal inhibition constant (Kd) of 150 nM when applied to ROMK1 channels expressed in Xenopus laevis oocytes. That the delta-dendrotoxin binding site exists on separate K+ channel classes is shown by its high affinity for two of the voltage-gated family of channels, Kv1.1 (Kd < 0.1 nM) and Kv1.6 (Kd = 23 nM). Single amino acid substitutions in ROMK1 indicate that delta-dendrotoxin binds to the pore region of ROMK1 even though it does not completely block conduction through the pore. These results suggest that dendrotoxins inhibit K+ channels by recognizing the structurally conserved pore region of these channels.

Structural conservation in prokaryotic and eukaryotic potassium channels

Toxins from scorpion venom interact with potassium channels. Resin-attached, mutant K+ channels from Streptomyces lividans were used to screen venom from Leiurus quinquestriatus hebraeus, and the toxins that interacted with the channel were rapidly identified by mass spectrometry. One of the toxins, agitoxin2, was further studied by mutagenesis and radioligand binding. The results show that a prokaryotic K+ channel has the same pore structure as eukaryotic K+ channels. This structural conservation, through application of techniques presented here, offers a new approach for K+ channel pharmacology.

The structure of the potassium channel: molecular basis of K+ conduction and selectivity

The potassium channel from Streptomyces lividans is an integral membrane protein with sequence similarity to all known K+ channels, particularly in the pore region. X-ray analysis with data to 3.2 angstroms reveals that four identical subunits create an inverted teepee, or cone, cradling the selectivity filter of the pore in its outer end. The narrow selectivity filter is only 12 angstroms long, whereas the remainder of the pore is wider and lined with hydrophobic amino acids. A large water-filled cavity and helix dipoles are positioned so as to overcome electrostatic destabilization of an ion in the pore at the center of the bilayer. Main chain carbonyl oxygen atoms from the K+ channel signature sequence line the selectivity filter, which is held open by structural constraints to coordinate K+ ions but not smaller Na+ ions. The selectivity filter contains two K+ ions about 7.5 angstroms apart. This configuration promotes ion conduction by exploiting electrostatic repulsive forces to overcome attractive forces between K+ ions and the selectivity filter. The architecture of the pore establishes the physical principles underlying selective K+ conduction.

Purification, characterization, and synthesis of an inward-rectifier K+ channel inhibitor from scorpion venom

We have purified a protein inhibitor of an inward-rectifier K+ channel, ROMK1, from the venom of the scorpion Leiurus quinquestriatus var. hebraeus. The inhibitor is Lq2, a previously discovered blocker of voltage- and Ca2+-activated K+ channels. Mutations were made on the channel and the inhibitor, and the resulting effects were examined using an electrophysiological assay. The data show that Lq2 blocks the pore of ROMK1, and that the interaction surface on Lq2 is the same for binding to inward-rectifier, voltage-activated, or Ca2+-activated K+ channels. These findings support the notion that different classes of K+ channels have different gates but a similar K+-selective pore structure.

Hanatoxin modifies the gating of a voltage-dependent K+ channel through multiple binding sites

We studied the mechanism by which Hanatoxin (HaTx) inhibits the drk1 voltage-gated K+ channel. HaTx inhibits the K+ channel by shifting channel opening to more depolarized voltages. Channels opened by strong depolarization in the presence of HaTx deactivate much faster upon repolarization, indicating that toxin bound channels can open. Thus, HaTx inhibits the drk1 K+ channel, not by physically occluding the ion conduction pore, but by modifying channel gating. Occupancy of the channel by HaTx was studied using various strength depolarizations. The concentration dependence for equilibrium occupancy as well as the kinetics of onset and recovery from inhibition indicate that multiple HaTx molecules can simultaneously bind to a single K+ channel. These results are consistent with a simple model in which HaTx binds to the surface of the drk1 K+ channel at four equivalent sites and alters the energetics of channel gating.

Mapping the receptor site for hanatoxin, a gating modifier of voltage-dependent K+ channels

Hanatoxin (HaTx) binds to multiple sites on the surface of the drk1 voltage-gated K+ channel and modifies channel gating. We set out to identify channel residues that contribute to form these HaTx binding sites. Chimeras constructed using the drk1 and shaker K+ channels suggest that the S3-S4 linker may contain influential residues. Alanine scanning mutagenesis of the region extending from the C terminal end of S3 through S4 identified a number of residues that likely contribute to form the HaTx binding sites. The pore blocker Agitoxin2 and the gating modifier HaTx can simultaneously bind to individual K+ channels. These results suggest that residues near the outer edges of S3 and S4 form the HaTx binding sites and are eccentrically located at least 15 A from the central pore axis on the surface of voltage-gated K+ channels.

Crystal structures of a complexed and peptide-free membrane protein-binding domain: molecular basis of peptide recognition by PDZ

Modular PDZ domains, found in many cell junction-associated proteins, mediate the clustering of membrane ion channels by binding to their C-terminus. The X-ray crystallographic structures of the third PDZ domain from the synaptic protein PSD-95 in complex with and in the absence of its peptide ligand have been determined at 1.8 angstroms and 2.3 angstroms resolution, respectively. The structures reveal that a four-residue C-terminal stretch (X-Thr/Ser-X-Val-COO(-)) engages the PDZ domain through antiparallel main chain interactions with a beta sheet of the domain. Recognition of the terminal carboxylate group of the peptide is conferred by a cradle of main chain amides provided by a Gly-Leu-Gly-Phe loop as well as by an arginine side chain. Specific side chain interactions and a prominent hydrophobic pocket explain the selective recognition of the C-terminal consensus sequence.

Contribution of the S4 segment to gating charge in the Shaker K+ channel

Voltage-activated ion channels respond to changes in membrane voltage by coupling the movement of charges to channel opening. A K+ channel-specific radioligand was designed and used to determine the origin of these gating charges in the Shaker K+ channel. Opening of a Shaker K+ channel is associated with a displacement of 13.6 electron charge units. Gating charge contributions were determined for six of the seven positive charges in the S4 segment, an unusual amino acid sequence in voltage-activated cation channels consisting of repeating basic residues at every third position. Charge-neutralizing mutations of the first four positive charges led to large decreases (approximately 4 electron charge units each) in the gating charge; however, the gating charge of Shaker delta 10, a Shaker K+ channel with 10 altered nonbasic residues in its S4 segment, was found to be identical to the wild-type channel. These findings show that movement of the NH2-terminal half but not the CO2H-terminal end of the S4 segment underlies gating charge, and that this portion of the S4 segment appears to move across the entire transmembrane voltage difference in association with channel activation.

Agitoxin footprinting the shaker potassium channel pore

In voltage-dependent K+ channels, each of the four identical subunits contributes one pore loop to the central ion selectivity unit at the interface between the subunits. The pore loop is also the target for scorpion venom peptide inhibitors. These inhibitors bind at the pore entryway between the four subunits and can assume any one of four orientations. The orientations become distinguishable only if the binding site symmetry is disrupted. We have used mutagenesis and site-directed chemical modification to alter pore loop amino acids in either one or four subunits. The effects of these alterations on inhibitor affinity define the eccentricity of amino acids in the pore entryway and imply a different secondary structure for the amino and carboxyl ends of the pore loop.

Spatial localization of the K+ channel selectivity filter by mutant cycle-based structure analysis

The structurally well-characterized scorpion toxin Agitoxin2 inhibits ion permeation through Shaker K+ channels by binding to the external pore entryway. Scanning mutagenesis identified a set of inhibitor residues critical for making energetic contacts with the channel. Using thermodynamic mutant cycle analysis, we have mapped channel residues relative to the known inhibitor structure. This study constrains the position of multiple channel residues within the pore-forming loops; in one stretch, we have been able to map five out of seven contiguous residues to the inhibitor interaction surface, including those involved in ion selectivity. One interaction in particular, that of K27M on the inhibitor with Y445F on the channel, is unique in that it depends on the K+ ion concentration. These results reveal a shallow vestibule formed by the pore loops at the K+ channel entryway. The selectivity filter is located at the center of the vestibule close to (approximately 5 A) the extracellular solution.

Divalent cation selectivity in a cyclic nucleotide-gated ion channel

Divalent metal cation selectivity was studied in guanosine 3',5'-cyclic monophosphate-gated ion channels. Channels from bovine retina were expressed in Xenopus laevis oocytes, and currents were measured using tight-seal patch recording methods. The ability of divalent cations to block Na+ currents was used to determine the occupancy of divalent cations in the ion conduction pore. At positive membrane voltages, where extracellular divalent cations are near equilibrium with their binding site, the occupancy reflects the affinity of the blocking ion. The selectivity sequence based on relative affinity was Ca2+ > Mg2+ = Sr2+ = Ba2+. In addition to its higher affinity, Ca2+ was more permeant and blocked with a weaker voltage dependence. Ca2+ was the only ion that blocked with a high Hill coefficient (n = 2.7), suggesting the presence of multiple binding sites. When Glu 363, located in the pore-forming region, was mutated to Asp, the affinity of all four ions increased and the selectivity sequence became Ca2+ > Sr2+ > Ba2+ > Mg2+. These results show that the channel is highly selective for Ca2+ and that Glu 363 mediates divalent cation selectivity of the channel.

Probing a potassium channel pore with an engineered protonatable site

Blockade by intracellular cations reduces outward conduction of K+ in inward rectifier K+ channels. Mutations of residue 171 in the second transmembrane (M2) segment of the ROMK1 channel have been found to affect the affinity for blockade by intracellular Mg2+ and polyamines. In the present study, we examined the mechanism by which this residue mediates blockade by placing a proton acceptor (histidine) at this position. The results allow us to draw two conclusions. First, the side chain of residue 171 is located in the ion conduction pore about halfway across the transmembrane voltage drop. Second, its side chain comes into close contact and interacts electrostatically with a blocking ion.

An inhibitor of the Kv2.1 potassium channel isolated from the venom of a Chilean tarantula

The Kv2.1 voltage-activated K+ channel, a Shab-related K+ channel isolated from rat brain, is insensitive to previously identified peptide inhibitors. We have isolated two peptides from the venom of a Chilean tarantula, G. spatulata, that inhibit the Kv2.1 K+ channel. The two peptides, hanatoxin1 (HaTx1) and hanatoxin2 (HaTx2) are unrelated in primary sequence to other K+ channel inhibitors. The activity of HaTx was verified by synthesizing it in a bacterial expression system. The concentration dependence for both the degree of inhibition at equilibrium (Kd = 42 nM) and the kinetics of inhibition (kon = 3.7 x 10(4) M-1s-1; koff = 1.3 x 10(-3) s-1), are consistent with a bimolecular reaction between HaTx and the Kv2.1 K+ channel. Shaker-related, Shaw-related, and eag K+ channels were relatively insensitive to HaTx, whereas a Shal-related K+ channel was sensitive. Regions outside the scorpion toxin binding site (S5-S6 linker) determine sensitivity to HaTx. HaTx introduces a new class of K+ channel inhibitors that will be useful probes for studying K+ channel structure and function.

Solution structure of the potassium channel inhibitor agitoxin 2: caliper for probing channel geometry

The structure of the potassium channel blocker agitoxin 2 was solved by solution NMR methods. The structure consists of a triple-stranded antiparallel beta-sheet and a single helix covering one face of the beta-sheet. The cysteine side chains connecting the beta-sheet and the helix form the core of the molecule. One edge of the beta-sheet and the adjacent face of the helix form the interface with the Shaker K+ channel. The fold of agitoxin is homologous to the previously determined folds of scorpion venom toxins. However, agitoxin 2 differs significantly from the other channel blockers in the specificity of its interactions. This study was thus focused on a precise characterization of the surface residues at the face of the protein interacting with the Shaker K+ channel. The rigid toxin molecule can be used to estimate dimensions of the potassium channel. Surface-exposed residues, Arg24, Lys27, and Arg31 of the beta-sheet, have been identified from mutagenesis studies as functionally important for blocking the Shaker K+ channel. The sequential and spatial locations of Arg24 and Arg31 are not conserved among the homologous toxins. Knowledge on the details of the channel-binding sites of agitoxin 2 formed a basis for site-directed mutagenesis studies of the toxin and the K+ channel sequences. Observed interactions between mutated toxin and channel are being used to elucidate the channel structure and mechanisms of channel-toxin interactions.

The cosmid CSSM25 assigns syntenic group U2 to bovine chromosome 9 and is localized to ovine chromosome 8

The cosmid-derived microsatellite CSSM 25 has previously been shown to map to bovine syntenic group U2 by linkage and hybrid somatic cell analysis. We have mapped the cosmid by fluorescent in situ hybridization to bovine Chromosome (Chr) 9q17-21 and ovine Chr 8q17-21 and hence assign U2 to Chr 9 in cattle. Bovine Chr 9 and ovine Chr 8 show strong banding pattern homology, and the localization of CSSM 25 to the same region confirms the strong conservation of gene locations on these chromosomes.

Revealing the architecture of a K+ channel pore through mutant cycles with a peptide inhibitor

Thermodynamic mutant cycles provide a formalism for studying energetic coupling between amino acids on the interaction surface in a protein-protein complex. This approach was applied to the Shaker potassium channel and to a high-affinity peptide inhibitor (scorpion toxin) that binds to its pore entryway. The assignment of pairwise interactions defined the spatial arrangement of channel amino acids with respect to the known inhibitor structure. A strong constraint was placed on the Shaker channel pore-forming region by requiring its amino-terminal border to be 12 to 15 angstroms from the central axis. This method is directly applicable to sodium, calcium, and other ion channels where inhibitor or modulatory proteins bind with high affinity.

Transfer of the scorpion toxin receptor to an insensitive potassium channel

Voltage-dependent potassium channels belong to a family of structurally related cation channels that underlie the electrical activity of excitable cells. Many potassium channels are blocked with high affinity by scorpion toxins, whereas others are completely insensitive. We transferred toxin sensitivity from the highly sensitive Kv1.3 (KV3) to the insensitive Kv2.1 (DRK1) potassium channel by transferring the stretch of amino acids between transmembrane domains 5/6. We provide evidence that this S5-S6 linker, which has been shown to comprise the pore-forming region, is probably the only part of the ion channel that directly interacts with bound toxin. Using site-directed mutagenesis, we identified specific residues in the S5-S6 linker that are responsible for the acquisition of toxin sensitivity by Kv2.1.

Two identical noninteracting sites in an ion channel revealed by proton transfer

The functional consequences of single proton transfers occurring in the pore of a cyclic nucleotide-gated channel were observed with patch recording techniques. These results led to three conclusions about the chemical nature of ion binding sites in the conduction pathway: The channel contains two identical titratable sites, even though there are more than two (probably four) identical subunits; the sites are formed by glutamate residues that have a pKa (where K(a) is the acid constant) of 7.6; and protonation of one site does not perturb the pKa of the other. These properties point to an unusual arrangement of carboxyl side-chain residues in the pore of a cation channel.

Electrostatic tuning of Mg2+ affinity in an inward-rectifier K+ channel

Inward-rectifier potassium channels conduct K+ across the cell membrane more efficiently in the inward than outward direction. This unusual conduction property is directly related to the biological action of these channels. One basis for inward rectification is voltage-dependent blockade by intracellular Mg2+ (refs 1, 7-9): strong inward-rectifier channels are so sensitive to intracellular Mg2+ that no outward K+ current is measurable under physiological conditions; weak inward rectifiers are less sensitive and allow some K+ to flow outwards. Background K1 channels and acetylcholine-regulated K+ channels from the heart are examples of strong inward rectifiers and ATP-sensitive K+ channels are weak rectifiers. Here we show that mutations at one position in the second transmembrane segment can alter the Mg2+ affinity and convert a weakly rectifying channel (ROMK1) into a strong rectifier. The amino acid at this position exposes its side chain to the aqueous pore and affects Mg2+ blockade as well as K+ conduction through an electrostatic mechanism.

A conductance maximum observed in an inward-rectifier potassium channel

One prediction of a multi-ion pore is that its conductance should reach a maximum and then begin to decrease as the concentration of permeant ion is raised equally on both sides of the membrane. A conductance maximum has been observed at the single-channel level in gramicidin and in a Ca(2+)-activated K+ channel at extremely high ion concentration (> 1,000 mM) (Hladky, S. B., and D. A. Haydon. 1972. Biochimica et Biophysica Acta. 274:294-312; Eisenmam, G., J. Sandblom, and E. Neher. 1977. In Metal Ligand Interaction in Organic Chemistry and Biochemistry. 1-36; Finkelstein, P., and O. S. Andersen. 1981. Journal of Membrane Biology. 59:155-171; Villarroel, A., O. Alvarez, and G. Eisenman. 1988. Biophysical Journal. 53:259a. [Abstr.]). In the present study we examine the conductance-concentration relationship in an inward-rectifier K+ channel, ROMK1. Single channels, expressed in Xenopus oocytes, were studied using inside-out patch recording in the absence of internal Mg2+ to eliminate blockade of outward current. Potassium, at equal concentrations on both sides of the membrane, was varied from 10 to 1,000 mM. As K+ was raised from 10 mM, the conductance increased steeply and reached a maximum value (39 pS) at 300 mM. The single-channel conductance then became progressively smaller as K+ was raised beyond 300 mM. At 1000 mM K+, the conductance was reduced to approximately 75% of its maximum value. The shape of the conductance-concentration curve observed in the ROMK1 channel implies that it has multiple K(+)-occupied binding sites in its conduction pathway.

Purification and characterization of three inhibitors of voltage-dependent K+ channels from Leiurus quinquestriatus var. hebraeus venom

Three new toxins from the venom of the scorpion Leiurus quinquestriatus var. hebraeus have been identified on the basis of their ability to block the Shaker K+ channel. These toxins have been purified using HPLC techniques and characterized as 38 amino acid peptides by mass spectroscopy, amino acid analysis, and sequence determination. Their chemical identity was confirmed by producing fully functional synthetic toxins using recombinant methods. These peptides are potent inhibitors of the Shaker K+ channel (Kd < 1 nM) as well as the mammalian homologues of Shaker. They are related to other previously described K+ channel toxins, but form a new subclass within the larger family of K+ channel inhibitors derived from scorpion venom. We have named these toxins agitoxin 1, 2, and 3, respectively.

Mutations in the K+ channel signature sequence

Potassium channels share a highly conserved stretch of eight amino acids, a K+ channel signature sequence. The conserved sequence falls within the previously defined P-region of voltage-activated K+ channels. In this study we investigate the effect of mutations in the signature sequence of the Shaker channel on K+ selectivity determined under bi-ionic conditions. Nonconservative substitutions of two threonine residues and the tyrosine residue leave selectivity intact. In contrast, mutations at some positions render the channel nonselective among monovalent cations. These findings are consistent with a proposal that the signature sequence contributes to a selectivity filter. Furthermore, the results illustrate that the hydroxyl groups at the third and fourth positions, and the aromatic group at position seven, are not essential in determining K+ selectivity.

Conduction properties of the cloned Shaker K+ channel

The conduction properties of the cloned Shaker K+ channel were studied using electrophysiological techniques. Single channel conductance increases in a sublinear manner with symmetric increases in K+ activity, reaching saturation by 0.6 M K+. The Shaker K+ channel is highly selective among monovalent cations; under bi-ionic conditions, its selectivity sequence is K+ > Rb+ > NH+4 > Cs+ > Na+, whereas, by relative conductance in symmetric solutions, it is K+ > NH+4 > Rb+ > Cs+. In Cs+ solutions, single channel currents were too small to be measured directly, so nonstationary fluctuation analysis was used to determine the unitary Cs+ conductance. The single channel conductance displays an anomalous molefraction effect in symmetric mixtures of K+ and NH+4, suggesting that the conducting pore is occupied by multiple ions simultaneously.

Functional stoichiometry of Shaker potassium channel inactivation

Shaker potassium channels from Drosophila are composed of four identical subunits. The contribution of a single subunit to the inactivation gating transition was investigated. Channels carrying a specific mutation in a single subunit can be labeled in a heterogeneous population and studied quantitatively with scorpion toxin sensitivity as a selection tag. Linkage within a single subunit of a mutation that removes the inactivation gate to a second mutation that affects scorpion toxin sensitivity demonstrates that only a single gate is necessary to produce inactivation. The inactivation rate constant for channels with a single gate was one-fourth that of channels with four gates. In contrast, the rate of recovery from inactivation was independent of the number of gates. It appears that each of the four open inactivation gates in a Shaker potassium channel is independent, but only one of the four gates closes in a mutually exclusive manner.