Jonathan D. Kibble

Properties of the cAMP-activated C1- current in choroid plexus epithelial cells isolated from the rat.

1. This study used whole‐cell patch clamp and RNA in situ hybridization experiments to determine whether the cAMP‐activated C1‐ current expressed in choroid plexus epithelial cells was carried by the cystic fibrosis transmembrane conductance regulator (CFTR) channel. 2. In patch clamp experiments, inclusion of 0.25 mM cAMP and 375 protein kinase A catalytic subunit (PKA) in the electrode solution caused activation of an inwardly rectifying current (21/23 cells). This current was C1‐ selective, since the current reversal potential (Erev) was ‐31 +/‐ 3 mV with equilibrium potential values for C1‐ (EC1) and Na+ (ENa) of ‐44 and 0 mV, respectively. 3. In anion substitution experiments, the relative anion permeability sequence for the inward rectifier was: I‐ (3.5) > HCO3‐(1.5) = C1‐(1.0) > Br‐(0.6) > aspartate (0.2). 4. The inward rectifier was sensitive to inhibition by a range of known channel inhibitors, including: glibenclamide (100 microns), DIDS (100 and 500 microns), NPPB (100 microns) and Ba2+ (1 mM). 5. In RNA in situ hybridization experiments, using two independent rat CFTR cRNA probes, expression of CFTR could not be detected in epithelial cells from the rat choroid plexus. 6. In conclusion, the cAMP‐dependent whole‐cell C1‐ current present in choroid plexus epithelial cells from the rat has properties which are distinctly different from those of CFTR.

A peer-led supplemental tutorial project for medical physiology: implementation in a large class

The purpose of this study was to evaluate the practicality of implementing a peer-teaching program in a large class (>350 students) of medical students and whether such a program is beneficial. Case-based problems were developed by faculty members to facilitate student problem solving and discussion. Voluntary student enrollment was available during the first week of a semester. Tutorials took place during out of class time and were facilitated by peers from the previous class. Tutors were selected for their outstanding performance in physiology; they were provided with training in facilitation skills and were given a package of model answers. Sixty-eight students enrolled in this pilot program and were organized into groups of approximately 8 students. On average, students attended four of six tutorials. Posttutorial quiz scores were significantly greater than paired pretest scores. Surveys showed that students had high expectations at the outset, which were matched with positive perceptions at the end of the tutorial program; the use of near-peer tutors was especially well received. Tutors also gave high approval ratings for their experiences. In conclusion, the peer tutoring program was logistically straightforward to implement in a large class and was endorsed by the participants.

Insights Gained from the Analysis of Performance and Participation in Online Formative Assessment

Background: Online quizzes are simple, cost-effective methods to provide formative assessment, but their effectiveness in enhancing learning and performance in medical education is unclear. Purpose: The purpose of this article is to determine the extent to which online quiz performance and participation enhances students’ performance on summative examinations. Methods: A retrospective case study investigating relationships between formative and summative assessment in terms of use and outcomes. Results: Online quiz scores and the rates of quiz participation were significantly correlated with corresponding performance on summative examinations. However, correlations were not dependent on the specific quiz content, and changes in patterns of quiz use were not reflected in corresponding changes in summative examination performance. Conclusions: The voluntary use of online quizzes, as well as the score attained, provides a useful general indicator of student performance but is unlikely to be sensitive enough to direct an individual students learning plan.

Voluntary participation in online formative quizzes is a sensitive predictor of student success

In a previous study ([1][1]) of online formative assessment in a medical school, I reported that scores on unsupervised online quizzes were predictive of outcomes on summative examinations. However, when no credit was assigned to the practice quizzes, the student participation rate was disappointing

A Ca2+-activated whole-cell Cl- conductance in human placental cytotrophoblast cells activated via a G protein.

Abstract. Whole-cell patch clamp experiments were performed on cultured human cytotrophoblast cells incubated for 24–48 hr after their isolation from term placentas. Cl−-selective currents were examined using K+-free solutions. Under nonstimulated conditions, most cells initially expressed only small background leak currents. However, inclusion of 0.2 mm GTPγS in the electrode solution caused activation of an outwardly rectifying conductance which showed marked time-dependent activation at depolarized potentials above +20 mV. Stimulation of this conductance by GTPγS was found to be Ca2+-dependent since GTPγS failed to activate currents when included in a Ca2+-free electrode solution. In addition, similar currents could be activated by increasing the [Ca2+] of the pipette solution to 500 nm. The Ca2+-activated conductance was judged to be Cl−-selective, since reversal potentials were predicted by Nernst equilibrium potentials for Cl−. This conductance could also be reversibly inhibited by addition of the anion channel blocker DIDS to the bath solution at a dose of 100 μm. Preliminary experiments indicated the presence of a second whole-cell anion conductance in human cytotrophoblast cells, which may be activated by cell swelling. Possible roles for the Ca2+-activated Cl− conductance in human placental trophoblast are discussed.

Adaptive downregulation of a quinidine-sensitive cation conductance in renal principal cells of TWIK-1 knockout mice

TWIK-1, a member of the two-pore domain K+ channel family, is expressed in brain, kidney, and lung. The aim of this study was to examine the effect of loss of TWIK-1 on the renal cortical collecting duct. Ducts were isolated from wild-type and TWIK-1 knockout mice by enzyme digestion and whole-cell clamp obtained via the basolateral membrane. Current- and voltage-clamp approaches were used to examine K+ conductances. No difference was observed between intercalated cells from wild-type or knockout ducts. In contrast, knockout principal cells were hyperpolarized compared to wild-type cells and had a reduced membrane conductance. This was a consequence of a fall in a barium-insensitive, quinidine-sensitive conductance (GQuin). GQuin demonstrated outward rectification and had a relatively low K+ to Na+ selectivity ratio. Loss of GQuin would be expected to lead to the hyperpolarization observed in knockout ducts by increasing fractional K+ conductance and Na+ uptake by the cell. Consistent with this hypothesis, knockout ducts had an increased diameter in comparison to wild-type ducts. These data suggest that GQuin contributes to the resting membrane potential in the cortical collecting duct and that a fall in GQuin could be an adaptive response in TWIK-1 knockout ducts.

Model explaining the relation between distal nephron Li + reabsorption and urinary Na + excretion in rats

Li+ may be reabsorbed via an amiloride-sensitive mechanism in the collecting ducts of rats administered a low-Na+ diet. This was investigated by measuring the increase in fractional urinary excretion of Li+(FELi) in response to amiloride in conscious rats at two different levels of plasma Li+ concentration and after administration of bendroflumethiazide (BFTZ), angiotensin III (ANG III), and aldosterone (Aldo). The results confirmed that amiloride increased (FELi) in rats on a low-Na+ diet (20 ± 1 to 35 ± 1%, means ± SE), whereas no increase was observed in rats on a normal Na+ diet (37 ± 1 to 38 ± 1%). The lithiuretic effect of amiloride was 1) abolished by preadministration of BFTZ (32 ± 1 to 33 ± 2%) to Na+-deprived rats and 2) increased by ANG III (27 ± 3 to 33 ± 2%) and Aldo (25 ± 2 to 37 ± 2%) in Na+-replete rats. Amiloride-induced changes in FELiwere independent of plasma Li+concentration but inversely related to the fractional excretion of Na+ and the amiloride-sensitive excretion of K+. These results are compatible with the hypothesis that a low tubular Na+ concentration reduces end-tubular Na+ reabsorption and results in hyperpolarization of the apical membrane, thus favoring Li+ uptake into the cells.

Estimated potassium reflection coefficient in perfused proximal convoluted tubules of the anaesthetized rat in vivo.

1. As yet there is no definitive description of the mechanism and route by which K+ reabsorption is achieved in the proximal convoluted tubule (PCT). We have assessed the contribution of convective K+ transport to net potassium ion flux (JK) by estimating the reflection coefficient of K+ (sigma K) in the proximal tubule of anaesthetized rats previously prepared for in vivo microperfusion. 2. Alterations in the luminal concentration of the impermeant solute raffinose in single‐perfused (lumen only) and double‐perfused (lumen and capillaries) PCTs were found to change fluid reabsorption in a predictable fashion. 3. Net potassium ion flux (JK) in single‐ and double‐perfused tubules was significantly correlated with net fluid flux (Jv), suggesting that convective K+ transport may be a significant factor in overall K+ transport by the PCT. 4. Estimates of sigma K in single‐ and double‐perfused tubules were very similar (0.14 +/‐ 0.06 and 0.13 +/‐ 0.05, respectively), even though K+ diffusion was not strictly controlled in the former group. The maximum effect of ‘pseudo‐solvent’ drag in double‐perfused tubules was estimated to give a sigma K of 0.40. This low value for sigma K suggests that true convection/solvent drag may be an important driving force for the reabsorption of K+ from the PCT of the rat.

Learning theories 101: application to everyday teaching and scholarship.

Shifts in educational research, in how scholarship in higher education is defined, and in how funding is appropriated suggest that educators within basic science fields can benefit from increased understanding of learning theory and how it applies to classroom practice. This article uses a mock curriculum design scenario as a framework for the introduction of five major learning theories. Foundational constructs and principles from each theory and how they apply to the proposed curriculum designs are described. A summative table that includes basic principles, constructs, and classroom applications as well as the role of the teacher and learner is also provided for each theory.

A Kir2.3-like K + Conductance in Mouse Cortical Collecting Duct Principal Cells

K+ channels play an important role in renal collecting duct cell function. The current study examined barium (Ba2+)-sensitive whole-cell K+ currents (IKBa) in mouse isolated collecting duct principal cells. IKBa demonstrated strong inward rectification and was inhibited by Ba2+ in a dose- and voltage-dependent fashion, with the Kd decreasing with hyperpolarization. The electrical distance of block by Ba2+ was around 8.5%. As expected for voltage-dependent inhibition, the association constant increased with hyperpolarization, suggesting that the rate of Ba2+ entry was increased at negative potentials. The dissociation constant also increased with hyperpolarization, consistent with the movement of Ba2+ ions into the intracellular compartment at negative potentials. These properties are not consistent with ROMK but are consistent with the properties of Kir2.3. Kir2.3 is thought to be the dominant basolateral K+ channel in principal cells. This study provides functional evidence for the expression of Kir2.3 in mouse cortical collecting ducts and confirms the expression of Kir2.3 in this segment of the renal tubule using reverse-transcriptase polymerase chain reaction. The conductance described here is the first report of a macroscopic K+ conductance in mouse principal cells that shares the biophysical profile of Kir2.3. The properties and dominant nature of the conductance suggest that it plays an important role in K+ handling in the principal cells of the cortical collecting duct.