Mark A. Walker

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Phosphinothricin is a non-selective herbicide which inhibits glutamine synthetase (EC 6.3.1.2) activity causing an overaccumulation of ammonia in higher plants. Alfalfa (Medicago sativa L) shoot tissue and petiole-derived callus exposed to phosphinothricin show 50 and 70% reductions, respectively, in glutamine synthetase activity with a concomitant rise of(More)
Calcium (Ca(2+)) plays many important regulatory roles in cardiac muscle cells. In the initial phase of the action potential, influx of Ca(2+) through sarcolemmal voltage-gated L-type Ca(2+) channels (LCCs) acts as a feed-forward signal that triggers a large release of Ca(2+) from the junctional sarcoplasmic reticulum (SR). This Ca(2+) drives heart muscle(More)
Stable calcium-induced calcium release (CICR) is critical for maintaining normal cellular contraction during cardiac excitation-contraction coupling. The fundamental element of CICR in the heart is the calcium (Ca(2+)) spark, which arises from a cluster of ryanodine receptors (RyR). Opening of these RyR clusters is triggered to produce a local, regenerative(More)
In the heart, electrical stimulation of cardiac myocytes increases the open probability of sarcolemmal voltage-sensitive Ca2+ channels and flux of Ca2+ into the cells. This increases Ca2+ binding to ligand-gated channels known as ryanodine receptors (RyR2). Their openings cause cell-wide release of Ca2+, which in turn causes muscle contraction and the(More)
Since its inception, philosophy has struggled to reconcile the apparent finitude of humans with the traditional telos of philosophy—the attempt to unite thought and Being, to arrive at absolute knowledge, at a final theory of everything. In response, some pragmatists, positivists, and philosophical naturalists have offered a deflationary account of(More)
BACKGROUND Although maternal group B streptococcus (GBS) infections are common, serious infections are rare with prompt diagnosis and treatment. We present 2 cases of GBS meningitis occurring 3 and 10 days after elective abortion. In the first patient, GBS meningitis was definitely related to the elective termination. In the second patient, however, no(More)
In a recent study of astrophysical “fine-tunings” (or “coincidences”), Robert Klee critically assesses the support that such astrophysical evidence might be thought to lend to the design argument (i.e., the argument that our universe has been designed by some deity). Klee argues that a proper assessment indicates that the universe is not as “fine-tuned” as(More)