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Biomedical subjects

H M Brown

Publications and source records attributed to H M Brown.

105 records · Page 6Linked to original sources
PubMed1971

Hyperpolarization of a barnacle photoreceptor membrane following illumination.

Membrane potential changes following illumination of a photoreceptor cell in the lateral ocellus of a barnacle (Balanus eburneus) were studied by means of intracellular recording and polarization techniques. Illumination produces a depolarizing response. When the illumination is terminated, the membrane potential temporarily becomes more negative than the resting potential prior to illumination. Although the amplitude of this postillumination hyperpolarization depends upon the intensity as well as the duration of the light pulse, the time course is fairly constant. The hyperpolarization is not associated with any significant membrane conductance increase and is abolished by 10(-5)M ouabain. It diminishes when the external Na or K ions are removed. An intracellular injection of Na ions produces a hyperpolarization similar to that following illumination. It is suggested that the postillumination hyperpolarization is produced by an electrogenic Na pump which is activated by the Na influx during illumination.

Animals↗
PubMed1970

Membrane properties of a barnacle photoreceptor examined by the voltage clamp technique.

1. Electrical properties of the membrane of photoreceptor cells in the lateral ocelli of barnacles, Balanus amphitrite and B. eburneus were investigated by intracellular recording, polarization and voltage-clamp techniques.2. The resting potential of a dark adapted cell was 36.3 +/- 6.6 mV (S.D.) and depended mainly on the external K(+) concentration.3. Current-voltage relations obtained from voltage-clamp experiments in the absence of light were non-linear and varied with time after the onset of a step change in membrane potential; the steady state was reached after about 0.5 sec.4. Illumination resulted in a membrane potential change under current clamp and in a change of membrane current (light-initiated membrane current (L.I.C.): total membrane current with illumination minus current without illumination) under voltage-clamp conditions. Amplitudes and time course of L.I.C. depended on the light intensity as well as membrane potential.5. The L.I.C.-voltage relation was non-linear and corresponded with a slope conductance increase with increasing positive membrane potential.6. The reversal potential of L.I.C. was independent of the light intensity and the time after onset of illumination; the average value obtained in normal saline was +26.9 +/- 5.0 mV.7. The membrane conductance estimated from instantaneous L.I.C.-voltage relations agreed with the chord conductance of the non-linear L.I.C.-voltage relation.8. Decreasing external Na(+) concentration decreased the inward component of L.I.C. but not the outward component.9. Decreasing external Ca(2+) concentration increased the inward as well as the outward component of L.I.C.10. The reversal potential shifted in the negative direction with decreasing external Na(+) concentration (the rate was 10-15 mV for a tenfold change in concentration) and the rate was augmented in the absence of Ca(2+) but did not exceed 21 mV.11. The change of reversal potential with changes of external Ca(2+) concentration was negligible in normal Na(+) media but was significant in the absence of Na(+) (rate as high as 20 mV).12. Alteration of the external K(+) or Cl(-) concentrations did not affect the amplitude or reversal potential of L.I.C.13. The results indicate that illumination increases the membrane permeability mainly to Na(+) ions and that the primary effect of Ca(2+) ions is suppression of the permeability increase; Ca(2+) permeability may increase slightly during illumination.

Animals↗
PubMed1969

Current-voltage relations during illumination: photoreceptor membrane of a barnacle.

In voltage clamped photoreceptor cells of the barnacle, light-induced membrane current varied nonlinearly with membrane potential and changed sign at about + 27 millivolts (reversal potential) independently of light intensity. Instantaneous current-voltage relations were linear and intersected the voltage axis at the reversal potential. Illumination increased membrane conductance that was dependent on membrane potential, light intensity, and time.

Animals↗
PubMed1968

Role of mites in allergy to house dust.

One hundred and thirty-two patients known or suspected of allergy to house dust were skin-tested with pure extracts of four varieties of dust mites. The results show that both Dermatophagoides culinae and D. pteronyssinus probably played important parts in sensitizing susceptible people, as did Glycyphagus destructor and G. domesticus in some cases. In some patients these results enabled successful desensitization against the dust to be carried out, and for corticosteroid therapy to be stopped. Hence the use of mite extracts is considered to be an important advance in the diagnosis of allergy to house dust.

Adult↗
PubMed1968

The electrical response of the planarian ocellus.

The planarian ocellar potential (OP), an action potential evoked from the planarian ocellus by a light flash, was recorded with microelectrodes. OP amplitude, latency, and peak delay varied as a function of stimulus intensity and state of adaptation in a manner similar to the responses of other photoreceptors. Changes in the OP that occurred with different directions of incident light are described and attributed to screening effects of the ocellar pigment cells. The temperature coefficient (Q(10)) of OP latency was 1.5; latency decreased continuously as temperature was increased to destructive levels. The energy of activation of the rate of OP formation was calculated to approximate 10 kcal. These findings suggest dependence of OP latency on ionic diffusion and of OP formation on a biocatalytic process.

Action Potentials↗
PubMed1968

Spectral sensitivity of the planarian ocellus.

The ocellar potential (OP) of planaria was recorded using microelectrode techniques. The action spectrum and spectral sensitivity of the OP are described. Maximum OP sensitivity was found with 508 nm light. A moderate increase in sensitivity to blue light was observed. This is typical of many invertebrate photoreceptors and was shown, by selective chromatic adaptation, not to indicate the presence of a second pigment.

Action Potentials↗
PubMedDate not supplied

Diagnosis of clinically unsuspected extrapulmonary tuberculosis by fine needle aspiration: a case report.

BACKGROUND: Mycobacterium tuberculosis (MTb) infection remains the cause of higher morbidity and mortality than any other infectious disease in the world. Intact cellular immunity is necessary to resist the disease, and therefore the AIDS epidemic has greatly contributed to the resurgence of MTb. Depending on the degree of immunosuppression, the presentation of MTb in patients with AIDS can be atypical and difficult to diagnose as compared to the classical presentation of MTb in the nonimmunocompromised population. CASE: A patient who was not known to be HIV positive had a clinical picture of extensive abdominal and pelvic lymphadenopathy without chest radiographic abnormalities. The diagnosis of MTb was made by fine needle aspiration (FNA) of a pelvic lymph node. CONCLUSION: Miliary tuberculosis associated with AIDS may have an unusual clinical presentation and unusual cytologic features on ENA.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

The fluorescent calcium indicator indo-1/AM inhibits renal proximal tubule cell volume regulation.

The intracellular calcium indicator, indo-1, is a fluorescent compound related in structure and function to the calcium chelator ethylene glycol-bis(beta-aminoethyl ether) tetraacetic acid (EGTA) that binds one calcium ion per molecule. In the extracellular range of 1 to 10 microM indo-1/AM, the estimated intracellular concentration of the dye is 0.1 to 3 microM. Therefore, it is likely that intracellular calcium signals could be blunted under these experimental conditions (Cai approximately 0.1 to 0.2 microM). To evaluate the potential effects of indo-1/AM on cellular function, proximal renal tubules of the teleost Carassius auratus (goldfish) were exposed to its acetoxymethyl ester (cell permeable form) in an isotonic Ringer's solution (290 mOsm, 0.1 mM calcium) followed by exposure to a low sodium hypotonic Ringer's (110 mOsm, 0.1 mM calcium). Cellular regulatory volume decreases (RVD) were determined with videometric methods. In proximal renal tubules incubated with indo-1/AM, RVD was inhibited in a dose-dependent fashion (3 to 5 microM). No effects on RVD were observed with the impermeant salt of indo-1. Overt cellular injury was found at 10 microM indo-1/AM as evidenced by mitochondrial and cell swelling, cellular detachment from the tubular basement membrane, and different degrees of cytolysis. It is postulated by us that the inhibitory effects of indo-1/AM (3-5 microM) on RVD are due to intracellular calcium chelation followed by disruption of intracellular signalling.

Animals↗