Electrical properties of the rabbit urinary bladder assessed using gramicidin D

Summary Recently, antibiotics have enjoyed widespread usage as tools in studies of epithelial transport. In the present study we assess the usefulness of the pore-forming antibiotic gramicidin D as a means for probing the electrical properties of the tight epithelium rabbit urinary bladder. Addition of 50 M gramicidin to the mucosal bath (either a NaCl or KCl Ringer's solution) led to a large irreversible increase in the transepithelial conductance (G _T ) within 800 sec.G _T increased by approximately 1200% and 500% in KCl and NaCl Ringer's solutions, respectively. Microelectrode measurements of the resistance ration (the ration of apical membrane resitance to basolateral membrane resistance) showed that apical membrane resistance is dereased by the drug. Measurements of the basolateral membrane resistance (R _bl ) and tight junctional resistance (R _j ) using a new and independent method (based on the perturbation of basolateral membrane electrogenic Na⁺ pump) demonstrated thatR _bl andR _j were unaffected, suggesting that the effects of gramicidin are restricted to the apical membrane for periods of at least 2 hours after drug addition. The selectivity of the gramicidin-induced permeability in the apical membrane was calculated from measurements of the apical membrane potential after ion substitutions using a modified version of the constant field equation. The selectivity sequence for cations was Cs⁺>K⁺>Na⁺>Li⁺>choline. Unlike the commonly used polyene antibiotics nystatin and amphotericin B, gramicidin did not induce a significant Cl^– permeability. In addition, the dose-response curve had a slope of 1. A method is described for calculating membrane resistances directly from transepithelial measurements under some conditions of gramicidin use, without requiring the use of microlectrode measurements.     

End-tidal CO2 response to low levels of inspired CO2 in awake beagle dogs

The steady-state end-tidal CO2 tension (PCO2) was examined during control and 1% CO2 inhalation periods in awake beagle dogs with an intact airway breathing through a low dead-space respiratory mask. A total of eight experiments were performed in four dogs, comprising 31 control observations and 23 CO2 inhalation observations. The 1% inhaled CO2 produced a significant increase in the steady-state end-tidal PCO2 comparable to the expected 1 Torr predicted from conventional CO2 control of ventilation. We conclude that 1% inhaled CO2 results in a hypercapnia. Any protocol that is to resolve the question of whether mechanisms are acting during low levels of inhaled CO2 such that ventilation increases without any change in arterial PCO2 must have sufficient resolving power to discriminate changes in gas tension in magnitude predicted from conventional (i.e., arterial PCO2) control of ventilation.     

Two replantations of severed ear parts.

Two successful cases of replantation of part of an ear are presented; both were done by simple suture. The larger of these replants consisted of a 13 x 43 mm segment of the superior helix and concha. Both were vascularized beofre 48 hours. The greatest problem was venous congestion. In the larger replant we made multiple puncture wounds daily on both sides of the graft with an 18-gauge needle to help relieve this.     

Recurrent abortion associated with a balanced 22;22 translocation,or isochromosome 22q in a monozygous twin

Summary A 45,XX,t(22;22)(p11;q11) or 45,XX,i(22q) chromosomal rearrangement was found in a woman with a history of recurrent abortion. A twin sister did not have the translocation even though marker studies indicate that the twins are probably monozygotic.     

Isolation and identification of pathogenic Naegleria from Florida lakes.

Five cases of primary amoebic meningoencephalitis associated with swimming in freshwater lakes have been recorded in Florida over the past 14 years. The present study demonstrated that pathogenic Naegleria, the causative agent, is relatively widespread. Twelve of 26 lakes sampled only once yielded the amoeba. Populations in three of five lakes sampled routinely reached levels of one amoeba per 25 ml of water tested during the hot summer months. Overwintering in freshwater lake bottom sediments was demonstrated, showing that thermal-discharge pollution of waters plays a miniscule, if any, role in the maintenance of pathogenic Naegleria in nature in this semitropical area.     

Interleukin-5, interleukin-3, and granulocyte-macrophage colony-stimulating factor cross-compete for binding to cell surface receptors on human eosinophils.

Human interleukin (IL)-5 receptors were characterized by means of binding studies using bioactive 125I-labeled IL-5. Of purified primary myeloid cells, eosinophils and basophils but not neutrophils or monocytes expressed surface receptors for IL-5. Binding studies showed that eosinophils expressed a single class of high affinity receptors (Ka = 1.2 x 10(10) M-1) with the number of receptors being small (less than 1000 receptors/cell) and varying between individuals. Among several cell lines examined only HL-60 cells showed detectable IL-5 receptors which were small in numbers (200 receptors/cell) and also bound 125I-IL-5 with high affinity. The binding of IL-5 was rapid at 37 degrees C while requiring several hours to reach equilibrium at 4 degrees C. Specificity studies revealed that the two other human eosinophilopoietic cytokines IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) inhibited the binding of 125I-IL-5 to eosinophils. No competition was observed by other eosinophil activating or nonactivating cytokines. The inhibition of 125I-IL-5 binding by IL-3 and GM-CSF was partial up to a concentration of competitor of 10(-7) M with GM-CSF consistently being the stronger competitor. Converse experiments using IL-5 as a competitor revealed that this cytokine inhibited the binding of 125I-IL-3 and of 125I-GM-CSF in some but not all the individuals tested, perhaps reflecting eosinophil heterogeneity in vivo. Cross-linking experiments on HL-60 cells demonstrated two IL-5-containing complexes of Mr 150,000 and Mr 80,000 both of which were inhibited by GM-CSF. The competition between IL-5, IL-3, and GM-CSF on the surface of mature eosinophils may represent a unifying mechanism that may help explain the common biological effects of these three eosinophilopoietic cytokines on eosinophil function. This unique pattern of competition may also be beneficial to the host by preventing excessive eosinophil stimulation.     

Notes on economic plants

Antibody-mediated sensitivity is not associated with cellular-mediated or delayed sensitivity, most frequently known as contact dermatitis. Compounds causing this response and their origins in plants are usually different, as is the immunological process.