Colony isolation and isozyme variability of the western seep fritillary, Speyeria nokomis apacheana (Nymphalidae), in the western Great Basin

Thirteen Speyeria nokomis apacheana (Edwards) (Nymphalidae) populations from the western Great Basin were assayed for isozyme variability using starch-gel electrophoresis. Eight of the 25 presumptive isozyme loci analyzed were found to be polymorphic. Collections made in 1991and 1992 allowed for between-year comparisons of heterozygosity and the estimation of effective population size for five of the sampled populations. Speyeria nokomis apacheana populations exhibit lower mean heterozygosity levels than other nymphalids. This may be attributed to genetic drift in apparently isolated populations with small effective sizes.     

Velocity and myosin phosphorylation transients in arterial smooth muscle: effects of agonist diffusion

Summary Transients in myoplasmic [Ca²⁺] and in phosphorylation of the 20,000 dalton light chain of myosin have been reported following stimulation of vascular smooth muscle by various agonists. Since these transients are rapid compared with the time required to attain a steady-state stress, agonist diffusion rates may be a significant limitation in activation. The purpose of this study was to estimate the effect of agonist diffusion rates on the time course of activation as assessed by mechanical measurements of stress development and isotonic shortening velocities and by determinations of the time course of myosin phosphorylation. The approach was to measure these parameters in K⁺-stimulated preparations of the swine carotid media of varying thicknesses and to estimate the theoretical contributions imposed by diffusion rates and the presence of a diffusion boundary layer surrounding the tissue. The results show that the time course of parameters which are tissue averages such as stiffness, active stress, and myosin phosphorylation is dominated by agonist diffusion rates. The sequence of events involved in excitation-contraction coupling including agonist actions on the cell membrane, Ca²⁺ release, activation of myosin light chain kinase, and cross-bridge phosphorylation appear to be very rapid events compared with stress development. Estimates of unloaded or lightly loaded shortening velocities which are not simple tissue averages appear to provide an imporoved estimate of activation rates.Supported by a grant from the National Institutes of Health 5-PO1-HL19242. K. E. Kamm was supported by a National Heart, Lung, and Blood Institute Research Service Award HL-05957.     

Inhibition of bacterial ice nucleators by fish antifreeze glycoproteins

Certain bacteria promote the formation of ice in super-cooled water by means of ice nucleators which contain a unique protein associated with the cell membrane. Ice nucleators in general are believed to act by mimicking the structure of an ice crystal surface, thus imposing an ice-like arrangement on the water molecules in contact with the nucleating surface and lowering the energy necessary for the initiation of ice formation. Quantitative investigation of the bacterial ice-nucleating process has recently been made possible by the discovery of certain bacteria that shed stable membrane vesicles with ice nucleating activity. The opposite effect, inhibition of ice formation, has been described for a group of glycoproteins found in different fish and insect species. This group of substances, termed antifreeze glycoproteins (AFGPs), promotes the supercooling of water with no appreciable effect on the equilibrium freezing point or melting temperature. Substantial evidence now indicates that AFGPs act by binding to a growing ice crystal and slowing crystal growth. As the ice-nucleating protein surface is believed to have a structure similar to an embryonic ice crystal, AFGPs might be predicted to interact directly with a bacterial ice-nucleating site. We report here that AFGPs from the antarctic fish Dissostichus mawsoni inhibit the ice-nucleating activity of membrane vesicles from the bacterium Erwinia herbicola. The inhibition effect shows saturation at high concentration of AFGP and conforms to a simple binding reaction between the AFGP and the nucleation centre.     

Photoreceptor light adaptation is mediated by cytoplasmic calcium concentration

The vertebrate visual system can operate over a large range of light intensities. This is possible in part because the sensitivity of photoreceptors decreases approximately in inverse proportion to the background light intensity. This process, called photoreceptor light adaptation, is known to be mediated by a diffusible intracellular messenger, but the identity of the messenger is still unclear. There has been considerable speculation that decreased cytoplasmic Ca2+ concentration (Cai2+) may play a role in light adaptation, and recent experiments in which Ca2+ buffer was incorporated into rod-cells have supported this notion. The extent of the contribution of calcium, however, remains unresolved. We now show that light-dependent changes in sensitivity in amphibian photoreceptors can be abolished by preventing movements of Ca2+ across the outer-segment plasma membrane. These experiments demonstrate that light adaptation in photoreceptors is mediated in cones primarily, and in rods perhaps exclusively, by changes in Cai2+.     

Anomalous stability of insulin at very high pressure

Summary Insulin is unaffected by pressures of 48,000 b in the solid state at room temperature, as elucidated both by spectroscopic measurements and bioassay. Its compression curve is reversible. The presence of water does not alter this property. Of a number of other proteins investigated insulin appears to be unique with regard to its pressure stability. The relative rigidity of the molecule combined with its small size may account for some of these properties.Acknowlegments. I should like to thank Prof. Willard F. Libby of the Department of Chemistry and Institute of Geophysics of the University of California, Los Angeles, for his interest and support of this study.     

Constituents ofCannabis sativa L. XXI: Estrogenic activity of a non-cannabinoid constituent

Summary A non-cannabinoid phenol (4,4,dihydroxy-5-methoxybibenzyl) increased uterine weight in prepubescent female rats, suggesting non-cannabinoids contribute to the estrogenic effects ofCannabis.Acknowledgments. This research was supported by Contract 271-78-3527 from the National Institute on Drug Abuse and by the Research Institute of Pharmaceutical Sciences, University of Mississippi. The authors are grateful to Karen S. Tomaszewski for technical assistance.