Ryanodine receptor of skeletal muscle is a gap junction-type channel

In the sarcoplasmic reticulum membrane of skeletal muscle, the ryanodine receptor forms an aqueous pore identified as the calcium-release pathway that operates during excitation-contraction coupling. The purified ryanodine receptor channel has now been shown to have four properties usually associated with gap junction channels: (i) a large nonspecific voltage-dependent conductance consisting of several open states; (ii) an inhibition of open probability by low pH; (iii) an inhibition of open probability by calcium; and (iv) a sensitivity to blockade by heptanol and octanol but not other alcohols. This functional homology may provide an insight into the mechanism of how muscle cells transduce depolarization into an intracellular release of calcium.     

Perspectives in Helioseismology

Helioseismology is probing the interior structure and dynamics of the sun with ever-increasing precision, providing a well-calibrated laboratory in which physical processes can be studied under conditions that are unattainable on Earth. Nearly 10 million resonant modes of oscillation are observable in the solar atmosphere, and their frequencies need to be known with great accuracy in order to gauge the sun's interior. The advent of nearly continuous imaged observations from the complementary ground-based Global Oscillation Network Group (GONG) observatories and the space-based Solar and Heliospheric Observatory instruments augurs a new era of discovery. The flow of early results from GONG resolves some issues and raises a number of theoretical questions whose answers are required for understanding how a seemingly ordinary star actually operates.     

Conviction seeking efficacy: Sustainable agriculture and the politics of co-optation

Proponents of sustainable agriculture seek deeply rooted social changes, but to advance this agenda requires political credibility and work with diverse partners. Asthe literature on political co-optation makesclear, the tension between conviction andcredibility is persistent and unavoidable; nota problem to be solved so much as a built-incondition of movement politics. Drawing on acase history of California's largestsustainable agriculture organization, astructural assessment is made of the strategicchoices facing movement leaders, organizationaltensions that accompany these choices, andperceived gains and losses. The case historydemonstrates how movement leaders craft middlerange strategies that adapt to politicalcircumstances while retaining attachments tocore values and constituencies. Thesestrategies are ripe with tradeoffs, placingdemands on leaders who must implement them in aspirit that sustains organizational vitalitywhile broadening political and social impact.But they also enlarge the democraticsensibilities of movement leaders, increasingtheir ability to listen, learn, and forgealliances based on shared goals rather thansimilar motives.     

Reconstitution of DNA segregation driven by assembly of a prokaryotic actin homolog

Multiple unrelated polymer systems have evolved to partition DNA molecules between daughter cells at division. To better understand polymer-driven DNA segregation, we reconstituted the three-component segregation system of the R1 plasmid from purified components. We found that the ParR/parC complex can construct a simple bipolar spindle by binding the ends of ParM filaments, inhibiting dynamic instability, and acting as a ratchet permitting incorporation of new monomers and riding on the elongating filament ends. Under steady-state conditions, the dynamic instability of unattached ParM filaments provides the energy required to drive DNA segregation.     

An expanded palette of genetically encoded Ca²⁺ indicators

Engineered fluorescent protein (FP) chimeras that modulate their fluorescence in response to changes in calcium ion (Ca(2+)) concentration are powerful tools for visualizing intracellular signaling activity. However, despite a decade of availability, the palette of single FP-based Ca(2+) indicators has remained limited to a single green hue. We have expanded this palette by developing blue, improved green, and red intensiometric indicators, as well as an emission ratiometric indicator with an 11,000% ratio change. This series enables improved single-color Ca(2+) imaging in neurons and transgenic Caenorhabditis elegans. In HeLa cells, Ca(2+) was imaged in three subcellular compartments, and, in conjunction with a cyan FP-yellow FP-based indicator, Ca(2+) and adenosine 5'-triphosphate were simultaneously imaged. This palette of indicators paints the way to a colorful new era of Ca(2+) imaging.     

Nitrogen-15 Dioxide Uptake and Incorporation by Phaseolus vulgaris (L.)

The sorption rate and metabolic fate of nitrogen dioxide, a major air pollutant, have been determined for Phaseolus vulgaris (L.). Sorption was determined kinetically by chemiluminescent monitoring of (15)NO(2) removal from the test atmosphere and directly by mass spectrometric analysis of nitrogen derived from the plant tissue. Sorptive processes were first order with respect to (15)NO(2) concentration. Virtually all of the (15)NO(2) taken up was metabolized.