Analysis of the rhodopsin cycle in limulus ventral photoreceptors using the early receptor potential

The early receptor potential (ERP) was recorded intracellularly from Limulus ventral photoreceptors. The ERP in cells dissected under red light was altered by exhaustive illumination. No recovery to the original wafeform was observed, even after 1 h in the dark. The ERP waveform could be further altered by chromatic adaptation or by changes in pH. The results indicate that at pH 7.8 there are two interconvertible pigment states with only slightly different lambdamax, whereas at pH 9.6 there are two interconvertible states with very different lambdamax. Under all conditions studied the ERPs were almost identical with those previously obtained in squid retinas. This strongly suggests that light converts Limulus rhodopsin to a stable photoequilibrium mixture of rhodopsin to a stable photoequilibrium mixture of rhodopsin and metarhodopsin and that, as in squid, the lambdamax of metarhodopsin depends on pH. This conversion at pH 7.8 is associated with a small (0.7 log unit) decrease in the maximum sensitivity of the late receptor potential. Thus the component of adaptation linked to changes in rhodopsin concentration is unimportant in comparison to the "neural" component.     

Developing a regional recovery framework

A biological attack would present an unprecedented challenge for local, state, and federal agencies, the military, the private sector, and individuals on many fronts, ranging from vaccination and treatment to prioritization of cleanup actions to waste disposal. To prepare for recovery from this type of incident, the Seattle Urban Area Security Initiative (UASI) partners collaborated with military and federal agencies to develop a regional recovery framework. The goal was to identify key information that will assist policymakers and emergency managers in shortening the timeline for recovery and minimizing the economic and public health impacts of a catastrophic anthrax attack. Based on discussions in workshops, tabletop exercises, and interviews with local, state, federal, military, and private sector entities responsible for recovery, the authors identified goals, assumptions, and concepts of operation for various areas to address critical issues the region will face as recovery progresses. Although the framework is specific to a catastrophic, wide-area biological attack using anthrax, it was designed to be flexible and scalable so it could also serve as the recovery framework for an all-hazards approach in other regions and jurisdictions. Benefits from this process include enhanced coordination and collaboration across agencies, a more thorough understanding of the anthrax threat, an opportunity to proactively consider long-term recovery, and a better understanding of the specific policy questions requiring resolution.     

HORMONAL TREATMENT OF DISSEMINATED CANCER OF THE FEMALE BREAST

1. The University of California Medical Center at San Francisco is participating in a nationwide cooperative study attempting to improve hormonal therapy of disseminated breast cancer. A prospective protocol is followed in which the antitumor efficacy of an investigational compound is compared with that of a reference standard of known efficacy. Known variables (menopausal age and site of most significant metastasis) are randomized to distribute similar patients into experimental and control groups. Assignment of the therapeutic agent is made at random to avoid bias, and where feasible, neither patient nor investigator knows which compound is given.2. Primary hormonal therapy of objectively progressing disseminated breast cancer yields objective regressions in approximately 22 percent of patients treated with any of the following: testosterone propionate, 2-alpha methyldihydrotestosterone propionate (a derivative which produces less virilization) and oral diethylstilbestrol. The average duration of regression is 10 months.3. After primary hormonal therapy has ceased to be effective, secondary hormonal therapy produces fewer than 12 per cent objective regressions when conventional estrogens, androgens, corticoids, or surgical hypophysectomy are employed. The rate rises to 19-26 per cent if corticoids are combined with triiodothyronine, or if the less virilizing androgen, 2-alpha methyldihydrotestosterone propionate is used instead of other androgens. Surprisingly, hydrocortisone 30 mg. plus triiodothyronine 50 micrograms—an innocuous combination—proved as effective as doses producing Cushing''s phenomena.     

Zinc-induced neuronal death in cortical neurons.

Although Zn2+ is normally stored and released in the brain, excessive exposure to extracellular Zn2+ can be neurotoxic. The purpose of the present study was to determine the type of neuronal cell death, necrosis versus apoptosis, induced by Zn2+ exposure. Addition of 10-50 microM ZnCl2 to the bathing medium of murine neuronal and glial cell cultures induced, over the next 24 hrs., Zn2+-concentration-dependent neuronal death; some glial death also occurred with Zn2+ concentrations above 30 microM. The neuronal death induced by 20 microM Zn2+ was characterized by coarse chromatin condensation, the formation of apoptotic bodies, and internucleosomal DNA fragmentation. It was attenuated in cortical cell cultures prepared from mice null for the bax gene, and by the caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-CH2F (ZVAD, 100 microM), but not by the NMDA receptor antagonist, D-2-amino-5-phosphonovalerate (D-APV, 200 microM ). In contrast, the neuronal death induced by 50 microM Zn2+ was characterized by plasma membrane disruption and random DNA fragmentation; this death was attenuated by D-APV, but exhibited little sensitivity to ZVAD or deletion of bax. These results suggest that Zn2+ can induce cell death with characteristics of either apoptosis or necrosis, depending on the intensity of the Zn2+ exposure.     

Replication of DNA minicircles in kinetoplasts isolated from Crithidia fasciculata: structure of nascent minicircles.

We have previously described an isolated kinetoplast system from Crithidia fasciculata capable of ATP-dependent replication of kinetoplast DNA minicircles (L. Birkenmeyer and D.S. Ray, J. Biol. Chem. 261: 2362-2368, 1986). We present here the identification of two new minicircle species observed in short pulse-labeling experiments in this system. The earliest labeled minicircle species (component A) contains both nascent H and L strands and is heterogeneous in sedimentation and electrophoretic migration. Component A has characteristics consistent with a Cairns-type structure in which the L strand is the leading strand and the H strand is the lagging strand. The other new species (component B) has a nascent 2.5-kilobase linear L strand with a single discontinuity that mapped to either of two alternative origins located 180 degrees apart on the minicircle map. Component B could be repaired to a covalently closed form by Escherichia coli polymerase I and T4 ligase but not by T4 polymerase and T4 ligase. Even though component B has a single gap in one strand, it had an electrophoretic mobility on an agarose gel (minus ethidium bromide) similar to that of a supercoiled circle with three supertwists. Treatment of component B with topoisomerase II converted it to a form that comigrated with a nicked open circular form (replicative form II). These results indicate that component B is a knotted topoisomer of a kinetoplast DNA minicircle with a single gap in the L strand.     

The pH dependence of the inhibition of ascorbate oxidase by anions

Double-reciprocal plots of azide inhibition, with respect to ascorbate, of ascorbate oxidase indicate mixed-type inhibition at pH values above 6. This is in contrast to the simple competitive inhibition previously observed at pH 5.6. Linear replots of the slopes and intercepts of the double-reciprocal plots yield two inhibition constants. Both constants are pH dependent. Similar inhibition patterns are obtained with fluoride and thiocyanate. These results suggest the presence of two inhibitor binding sites, one of which is competitive with respect to ascorbate and the other uncompetitive.