Lauren K Barr

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It is generally thought that nexuses constitute low-resistance pathways between cell interiors in epithelial, neural, muscular, and even connective tissues. However, there are no reliable estimates of the specific resistance of a nexus. The reason for this is that in most cases the surfaces of nexuses between cells are geometrically complex and therefore it(More)
The electrical behavior of small single frog atrial trabeculae in the double sucrose gap has been investigated. The currents injected during voltage clamp experiments did not behave as predicted from the assumption of spatial uniformity of the voltage across a Hodgkin-Huxley membrane. Much of the difference is due to the geometrical complexities of this(More)
The mesencephalic and metencephalic region (MMR) of the vertebrate central nervous system develops in response to signals produced by the isthmic organizer (IsO). We have previously reported that the LIM homeobox transcription factor Lmx1b is expressed within the chick IsO, where it is sufficient to maintain expression of the secreted factor wnt1. In this(More)
As is common for amphibians, the sphincter pupillae of the axolotl contracts in vitro in response to illumination with visible light. 1. In a comparison of photomechanical responses of albino and normally pigmented axolotls, similar time courses and maxima of force development were found. 2. The dependence of isometric active force development on the length(More)
The time courses of isometrically recorded photomechanical responses of isolated sphincter pupillae of Rana pipiens can be accurately predicted by a set of differential equations derived from phosphorylation theory of smooth muscle contraction. We compared actual light-stimulated contractions with calculated ones over a wide range of stimulus intensities(More)
There is experimental evidence suggesting that the interstitial cells of Cajal are essential for rhythmic slow waves of the smooth muscle layers of the mammalian small intestine. Different investigators have identified them variously as modified neurons, glia, fibroblasts or modified smooth muscle cells. Since histological categorization bears on(More)
Catalase-peroxidase (KatG) is an enzyme capable of utilizing both catalase and peroxidase activity to break down hydrogen peroxide. Catalase activity by the enzyme generally dominates, but peroxidatic electron donors have been shown to stimulate catalase activity, likely by rescuing catalase-inactive intermediates resulting from off-pathway electron(More)
We analyze the behavior and the identification problem of cyclic four-state models. We find that for any state, or a weighted combination of two states, there can be at most one maximum, or one minimum, and two inflection points. We obtain necessary conditions for overshoot and undershoot and give examples. We describe procedures to estimate all the rate(More)
Cytosolic fractions of frog heart homogenates contain large amounts of a soluble, large molecular weight protein that binds the specific neurotoxin saxitoxin with the same high affinity as does the plasma membrane. Another neurotoxin, tetrodotoxin, which ordinarily is competitive with saxitoxin, does not displace saxitoxin from the cytosolic sites or from(More)
An equivalent electrical circuit has been constructed for small atrial trabecula of frog in a double sucrose gap voltage clamp apparatus. The basic strategy in constructing the circuit was to derive the distribution of membrane capacitance and extracellular resistance from the preparation's response to small voltage displacements near the resting condition,(More)
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