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Two-pore domain, outwardly rectifying potassium (TOK) channels are exclusively expressed in fungi. Human fungal pathogen TOK channels are potential antifungal targets, but TOK channel modulation in general is poorly understood. Here, we discovered that Candida albicans TOK (CaTOK) is regulated by extracellular pH, in contrast to TOK channels from other fungal species tested. Low pH increased CaTOK channel outward currents (pKa = 6.0), hyperpolarized the voltage-dependence of TOK activation, and increased pore selectivity for K+ over Na+, shifting the reversal potential (E REV) toward E K. Mutating H144 in the S1-S2 extracellular linker partially diminished pH sensitivity, suggesting H144 forms part of the CaTOK pH sensor. Functional analysis of chimeras made with pH-insensitive Saccharomyces cerevisiae TOK and point mutants revealed that CaTOK V462 and S466 in the final transmembrane segment complete the pH-responsive elements. A tripartite network of residues thus endows CaTOK with the ability to respond functionally to changes in pH.

TOKs are outwardly rectifying K+ channels in fungi with two pore-loops and eight transmembrane spans. Here, we describe the TOKs from four pathogens that cause the majority of life-threatening fungal infections in humans. These TOKs pass large currents only in the outward direction like the canonical isolate from Saccharomyces cerevisiae (ScTOK), and distinct from other K+ channels. ScTOK, AfTOK1 (Aspergillus fumigatus), and H99TOK (Cryptococcus neoformans grubii) are K+ -selective and pass current above the K+ reversal potential. CaTOK (Candida albicans) and CnTOK (Cryptococcus neoformans neoformans) pass both K+ and Na+ and conduct above a reversal potential reflecting the mixed permeability of their selectivity filter. Mutations in CaTOK and ScTOK at sites homologous to those that open the internal gates in classical K+ channels are shown to produce inward TOK currents. A favored model for outward rectification is proposed whereby the reversal potential determines ion occupancy, and thus, conductivity, of the selectivity filter gate that is coupled to an imperfectly restrictive internal gate, permitting the filter to sample ion concentrations on both sides of the membrane.

Voltage-gated potassium (Kv) currents generated by N-type α-subunit homotetramers inactivate rapidly because an N-terminal ball domain blocks the channel pore after activation. Hence, the inactivation rate of heterotetrameric channels comprising both N-type and non-N-type (delayed rectifier) α-subunits depends upon the number of N-type α-subunits in the complex. As Kv channel inactivation and inactivation recovery rates regulate cellular excitability, the composition and expression of these heterotetrameric complexes are expected to be tightly regulated. In a companion article, we showed that the single transmembrane segment ancillary (β) subunits KCNE1 and KCNE2 suppress currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels, by trapping them early in the secretory pathway. Here, we show that this trapping is prevented by coassembly of the N-type α-subunits with intra-subfamily delayed rectifier α-subunits. Extra-subfamily delayed rectifier α-subunits, regardless of their capacity to interact with KCNE1 and KCNE2, cannot rescue Kv1.4 or Kv3.4 surface expression unless engineered to interact with them using N-terminal A and B domain swapping. The KCNE1/2-enforced checkpoint ensures N-type α-subunits only reach the cell surface as part of intra-subfamily mixed-α complexes, thereby governing channel composition, inactivation rate, and-by extension-cellular excitability.

Potassium currents generated by voltage-gated potassium (Kv) channels comprising α-subunits from the Kv1, 2, and 3 subfamilies facilitate high-frequency firing of mammalian neurons. Within these subfamilies, only three α-subunits (Kv1.4, Kv3.3, and Kv3.4) generate currents that decay rapidly in the open state because an N-terminal ball domain blocks the channel pore after activation-a process termed N-type inactivation. Despite its importance to shaping cellular excitability, little is known of the processes regulating surface expression of N-type α-subunits, versus their slowly inactivating (delayed rectifier) counterparts. Here we found that currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels are all strongly suppressed by the single transmembrane domain ancillary (β) subunits KCNE1 and KCNE2. A combination of electrophysiological, biochemical, and immunofluorescence analyses revealed this suppression is due to KCNE1 and KCNE2 retaining Kv1.4 and Kv3.4 intracellularly, early in the secretory pathway. The retention is specific, requires α-β coassembly, and does not involve the dynamin-dependent endocytosis pathway. However, the small fraction of Kv3.4 that escapes KCNE-dependent retention is regulated by dynamin-dependent endocytosis. The findings illustrate two contrasting mechanisms controlling surface expression of N-type Kv α-subunits and therefore, potentially, cellular excitability and refractory periods.

Abstract Background Sodium bicarbonate (NaHCO3) is a well-established nutritional ergogenic aid, though gastrointestinal (GI) distress is a common side-effect. Delayed-release NaHCO3 may alleviate GI symptoms and enhance bicarbonate bioavailability following oral ingestion, although this has yet to be confirmed. Methods In a randomised crossover design, pharmacokinetic responses and acid-base status were compared following two forms of NaHCO3, as were GI symptoms. Twelve trained healthy males (mean ± SD age 25.8 ± 4.5 years, maximal oxygen uptake ( V̇O2max $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\max } $$) 58.9 ± 10.9 mL kg min−1, height 1.8 ± 0.1 m, body mass 82.3 ± 11.1 kg, fat-free mass 72.3 ± 10.0 kg) underwent a control (CON) condition and two experimental conditions: 300 mg kg−1 body mass NaHCO3 ingested as an aqueous solution (SOL) and encased in delayed-release capsules (CAP). Blood bicarbonate concentration, pH and base excess (BE) were measured in all conditions over 180 min, as were subjective GI symptom scores. Results Incidences of GI symptoms and overall severity were significantly lower (mean difference = 45.1%, P

Basic foot care is a real need of people experiencing homelessness. To improve access to foot health for this group, three services structured to provide healthcare support for people experiencing homelessness collaborated in metropolitan Melbourne, Australia: an established nurse-led Homeless Persons Program (HPP), a specialty community health podiatry clinic servicing people experiencing homelessness, and a charity supporting disadvantaged communities providing free socks, foot first aid kits and second-hand footwear for distribution by nurses and podiatrists of participating services. This paper outlines the implementation and evaluation of this collaboration. A four stage implementation approach was used, addressing: 1. Who needs to do what differently? 2. What are the barriers and enablers that need to be addressed? 3. Which intervention components could overcome the modifiable barriers and enhance the enablers? 4. How can the changes be measured? The evaluation prospectively collected information about how HPP nurses referred adults to podiatry, and whether the referred individuals accessed the podiatry clinic, the outcomes of the podiatry visit, and how many received footwear, socks and foot first aid kits provided by the non-profit organisation. Over 1st June 2019 and 31st December 2020, 52 individuals were identified as adults who could potentially benefit from podiatry by the HPP nurses, of which 33 accessed podiatry. Those who did not visit the podiatry clinic were more likely to be born outside of Australia, live in more precarious housing (crisis accommodation and rough sleeping), have slightly more predisposing factors for homelessness, but have fewer medical, psychological and cognitive conditions. A structured approach including processes, education, regular, outreach to youth refuges and formal outcome monitoring enabled foot health care access in people experiencing homelessness. Further research is needed to ascertain how to support participants at risk of foot problems to access podiatry before their foot health issue reaches crisis point. [ABSTRACT FROM AUTHOR]

Abstract Background Individual time to peak blood bicarbonate (HCO3 −) has demonstrated good to excellent reproducibility following ingestion of both 0.2 g kg−1 body mass (BM) and 0.3 g kg−1 BM sodium bicarbonate (NaHCO3), but the consistency of the time trial (TT) performance response using such an individualised NaHCO3 ingestion strategy remains unknown. This study therefore evaluated the reproducibility of 4-km TT performance following NaHCO3 ingestion individualised to time to peak blood bicarbonate. Methods Eleven trained male cyclists completed five randomised treatments with prior ingestion of 0.2 g kg−1 (SBC2) or 0.3 g kg−1 BM (SBC3) NaHCO3, on two separate occasions each, or a control trial entailing no supplementation. Participants completed a 4-km cycling TT on a Velotron ergometer where time to complete, power and speed were measured, whilst acid-base blood parameters were also recorded (pH and blood bicarbonate concentration HCO3 −) and lactate [La−]. Results Alkalosis was achieved prior to exercise in both SBC2 and SBC3, as pH and HCO3 − were greater compared to baseline (p 0.05). The reproducibility of the mean absolute change from baseline to peak in HCO3 − was good in SBC2 (r = 0.68) and excellent in SBC3 (r = 0.78). The performance responses following both SBC2 and SBC3 displayed excellent reproducibility (r range = 0.97 to 0.99). Conclusions Results demonstrate excellent reproducibility of exercise performance following individualised NaHCO3 ingestion, which is due to the high reproducibility of blood acid-base variables with repeat administration of NaHCO3. Using a time to peak HCO3 - strategy seems to cause no dose-dependent effects on performance for exercise of this duration and intensity; therefore, athletes may consider smaller doses of NaHCO3 to mitigate gastrointestinal (GI) discomfort.