Mutations at critical residue positions in transmembrane span 7 (TM7) of the serotonin transporter affect the Na ؉ dependence of transport. It was possible that these residues, which form a stripe along one side of the predicted ␣-helix, formed part of a water-filled pore for Na ؉ . We tested whether cysteine substitutions in TM7 were accessible to hydrophilic, membrane-impermeant methanethiosulfonate (MTS) reagents. Although all five cysteine-containing mutants tested were sensitive to these reagents, noncysteine control mutants at the same positions were in most cases equally sensitive. In all cases, MTS sensitivity could be traced to changes in accessibility of a native cysteine residue in extracellular loop 1, Cys-109. Moreover, none of the TM7 cysteines reacted with the biotinylating reagent MTSEA-biotin when tested in the C109A background. It is thus unlikely that the critical stripe forms part of a water-filled pore. Instead, studies of the ion dependence of the reaction between Cys-109 and MTS reagents lead to the conclusion that TM7 is involved in propagating conformational changes caused by ion binding, perhaps as part of the translocation mechanism. The critical stripe residues on TM7 probably represent a close contact region between TM7 and one or more other TMs in the transporter's three-dimensional structure.

Just-in-time training improved procedural confidence with infant LP, but work place busyness and instructor lack of support or unawareness were barriers to JITT performance. Optimal LP JITT would occur with improved contextual fidelity. More research is needed to determine optimal training strategies that are effective for the learner and maximize clinical outcomes for the patient.

Participation in a single SBME mastery learning session was insufficient to affect pediatric interns' subsequent procedural success.

The presence of air in the ascending colon on the 3-view abdominal radiograph can decrease the likelihood of or exclude intussusception. When clinical suspicion is low, the presence of specific criterion on a 3-view abdominal radiograph series may obviate the need for further studies.

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