IntroductionOrthodontic treatment is reimbursed by Medicaid based on orthodontic and financial need with qualifiers determined by individual states. Changes in Medicaid-funded orthodontic treatment following the “Great Recession” in 2007 and the enactment of the Affordable Care Act in 2010 were compared for the 50 United States and the District of Columbia to better understand disparities in access to care. The results from this 2015 survey were compared to data gathered in 2006 (1).Materials and methodsMedicaid officials were contacted by email, telephone, or postal mail regarding the age limit for treatment, practitioner type who can determine eligibility and provide treatment, records required for case review, and rate and frequency of reimbursement. When not attained by direct contact, the information was gleaned from online websites, provider manuals, and state orthodontists.ResultsInformation gathered from 50 states and the District of Columbia documents that Medicaid program characteristics and expenditures continue to vary by state. Expenditures and reimbursement rates have decreased since 2006 and vary widely by geographic region. Some states have tightened restrictions on qualifiers and increased submission requirements by providers.ConclusionThe variation and lack of uniformity that still exists among Medicaid orthodontic programs in different states creates disparities in orthodontic care for US citizens. Barriers to care for Medicaid-funded orthodontic treatment have increased since 2006.
Voltage clamp fluorimetry (VCF) utilizes fluorescent probes that covalently bind to cysteine residues introduced into proteins and emit light as a function of their environment. Measurement of this emitted light during membrane depolarization reveals changes in the emission level as the environment of the labelled residue changes. This allows for the correlation of channel gating events with movement of specific protein moieties, at nanosecond time resolution. Since the pioneering use of this technique to investigate Shaker potassium channel activation movements, VCF has become an invaluable technique used to understand ion channel gating. This review summarizes the theory and some of the data on the application of the VCF technique. Although its usage has expanded beyond voltage-gated potassium channels and VCF is now used in a number of other voltage- and ligand-gated channels, we will focus on studies conducted in Shaker potassium channels, and what they have told us about channel activation and inactivation gating.
The Kv1.2 channel, with its high resolution crystal structure, provides an ideal model for investigating conformational changes associated with channel gating, and fluorescent probes attached at the extracellular end of S4 are a powerful way to gain a more complete understanding of the voltage-dependent activity of these dynamic proteins. Tetramethylrhodamine-5-maleimide (TMRM) attached at A291C reports two distinct rearrangements of the voltage sensor domains, and a comparative fluorescence scan of the S4 and S3–S4 linker residues in Shaker and Kv1.2 shows important differences in their emission at other homologous residues. Kv1.2 shows a rapid decrease in A291C emission with a time constant of 1.5 ± 0.1 ms at 60 mV (n = 11) that correlates with gating currents and reports on translocation of the S4 and S3–S4 linker. However, unlike any Kv channel studied to date, this fast component is dwarfed by a larger, slower quenching of TMRM emission during depolarizations between −120 and −50 mV (τ = 21.4 ± 2.1 ms at 60 mV, V1/2 of −73.9 ± 1.4 mV) that is not seen in either Shaker or Kv1.5 and that comprises >60% of the total signal at all activating potentials. The slow fluorescence relaxes after repolarization in a voltage-dependent manner that matches the time course of Kv1.2 ionic current deactivation. Fluorophores placed directly in S1 and S2 at I187 and T219 recapitulate the time course and voltage dependence of slow quenching. The slow component is lost when the extracellular S1–S2 linker of Kv1.2 is replaced with that of Kv1.5 or Shaker, suggesting that it arises from a continuous internal rearrangement within the voltage sensor, initiated at negative potentials but prevalent throughout the activation process, and which must be reversed for the channel to close.
Accili (2009) The molecular basis for the actions of K V β1.2 on the opening and closing of the K V 1.2 delayed rectifier channel, Channels, 3:5, 314-322,
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