Elizabeth W. Stephenson

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Stimulation of sarcoplasmic reticulum Ca release by Mg reduction of caffeine was studied in situ, to characterize further the Ca2+ dependence observed previously with stimulation by Cl ion. 45Ca efflux and isometric force were measured simultaneously at 19 degrees C in frog skeletal muscle fibers skinned by microdissection; EGTA was added to chelate(More)
The membrane potential of vertebrate twitch fibers closely controls Ca fluxes between intracellular compartments, which in turn control contraction. Recent work on intracellular Ca movement is reviewed in the general context of current efforts to synthesize physiological, biochemical, and structural observations on the contractile mechanism and its(More)
Isometric force and 45Ca loss from fiber to bath were measured simultaneously in skinned fibers from frog muscle at 19 degrees C. In unstimulated fibers, 45Ca efflux from the sarcoplasmic reticulum (SR) was very slow, with little or no dependence on EGTA (0.1-5 mM) or Mg++ (20 micrometer-1.3 mM). Stimulation by high [Cl] at 0.11 mM Mg++ caused rapid force(More)
The c-fos protooncogene is transcriptionally activated by a wide variety of agents including serum, growth factors, and phorbol esters. This induction is rapid and transient and is mediated through a number of identified promoter elements. Growth hormone (GH) is also known to induce transcription of c-fos in a variety of cell types including NIH 3T3(More)
In frog stomach muscle fibers, normal steady-state K flux, estimated directly from 42K uptake, was 0.17 pmol/cm2 per s at 5 degrees C and 0.63 pmol/cm2 per s at 15 degrees C. Influx characteristics were studied at 5 degrees C, where backflux and diffusional delay effects are minimized. Steady-state K influx was a saturating function of external [K] over the(More)
Chloride-induced Ca release in skinned muscle fibers was studied by measuring isometric force transients and 45Ca loss from fiber to washout solutions. Skinned fibers prepared from muscles soaked in normal Ringer solution made large force transients in 120 mM Cl solution with 5 mM ATP and 1 mM Mg, but 3 mM Mg was inhibitory. Mg inhibition was antagonized by(More)
The effect of Mg on Ca movement between the sarcoplasmic reticulum (SR) and myofilament space (MFS) was studied in skinned muscle fibers by using isometric force as an indicator of MFS Ca. In Ca-loaded fibers at 20 degrees C, the large force spike induced by Ca in 1 mM Mg (5 mM ATP) was strongly inhibited in 3 mM Mg, and force development was extremely(More)
Excitation-contraction (E-C) coupling in skeletal muscle can be studied in skinned fibers by direct assay of 45Ca efflux and simultaneous isometric force, under controlled conditions. Recent work provides evidence that such studies can address major current questions about the mechanisms of signal transmission between transverse tubules and sarcoplasmic(More)
Cation composition of frog smooth muscle cells was investigated. Fresh stomach muscle rings resembled skeletal muscle, but marked Na gain and K loss followed immersion. Mean Na (49.8-79.7 mM/kg tissue) and K (61.8-80.1 mM/kg tissue) varied between batches, but were stable for long periods in vitro. Exchange of 6-30 mM Na/kg tissue with (22)Na was extremely(More)