Plasmodium knowlesi: Morphology and course of infection in rhesus monkeys treated with clindamycin and its N-demethyl-4′-pentyl analog

The clinical and morphologic effects of clindamycin and N-demethyl-4′-pentyl clindamycin were evaluated using Plasmodium knowlesi in rhesus monkeys. Both compounds cured blood-induced infections when administered daily for five consecutive days. When the rapidity of action of these antibiotics was compared with chloroquine it was evident that although they were able to control fulminating infections in all treated monkeys their effect was about 2 days slower than chloroquine in decreasing parasitemias and 3 to 4 days slower in clearing parasites from the blood. Morphologic changes within the parasite associated with drug action were studied in time sequences by light and electron microscopy. Changes were observed in the parasite ribosomes 24 hr after drug administration. Affected ribosomes showed electron-lucent zones measuring ~50 Å in the center. During the following 24 hr these changes became more prominent with foci in which disintegrated ribosomes were replaced by fine fibrillar material and the cisternae of the endoplasmic reticulum became dilated. By 72 hr this dilation was more apparent and resulted in abundant coalescence of vacuoles in the cytoplasm. Mitochondria became dilated with fibrils in the matrix, although the degree of swelling was not a conspicuous and constant feature. The nucleus presented a fine fibrillar appearance and fewer granules were seen than in normal parasites. The latter two observed changes appear to be secondary to changes in the ribosomes and probably are not directly related to the action of the antibiotics. These studies indicate that clindamycin and its analog affect primarily the ribosomes and their mode of action is different from that of the commonly used antimalarials.     

Monoclonal antibodies to parasite antigens found in the serum of Dirofilaria immitis-infected dogs

We recently reported that parasite antigens are detectable in the serum of Dirofilaria immitis-infected dogs by counterimmunoelectrophoresis (CIE). Hybridoma cell lines that produce monoclonal antibodies specific for these antigens were obtained by immunizing mice with a partially purified antigen preparation, fusing spleen cells with SP-2 myeloma cells, and screening cell culture supernatants for antibody by ELISA and CIE inhibition. Antibodies specific for two epitopes shared by the two major circulating parasite antigens were identified. Immunoperoxidase studies showed that the epitopes recognized by the monoclonals were widely distributed in D. immitis, but the female uterus and eggs were particularly strongly labeled. A monoclonal antibody-based ELISA was developed to measure parasite antigens in dog sera. Parasite antigens were detected in 45 of 46 sera from infected dogs but were absent in sera from uninfected dogs and sera from dogs infected with Dipetalonema reconditum. Serum antigen content was significantly correlated with the number of female worms recovered from infected dogs (r = 0.82, p less than 0.001). Antigenemia was first detected 6 mo after infection, and antigen levels remained fairly stable between 9 and 21 mo after infection. Parasite antigen detection with this monoclonal antibody-based ELISA appears to be superior to previously described diagnostic methods for canine dirofilariasis in terms of sensitivity, specificity, and relation to infection intensity.     

Some electrophysiological and permeability properties of the mouse egg

Certain electrophysiological and ionic properties of the mouse egg (CF-1 and BDF 12–18 hr post ovulation) have been investigated. Membrane potential (?14 ± 0.4 mV, ± SE, inside negative), membrane resistance (2610 ± 38 ohm·cm²), and membrane capacitance (1.6 ± 0.03 μF cm^?2) have been determined by means of intracellular microelectrode recording techniques. Membrane potential and related parameters are stable for extended periods of time upon impalement and the magnitude of the cell membrane potential has been demonstrated to be sensitive to alteration in external sodium. The electrophysiological studies in conjunction with measurements of unidirectional potassium fluxes using isotope tracer-techniques have allowed determination of membrane permeability to potassium (8 × 10^?8 cm sec^?1) and membrane potassium conductance (25 μmho cm^?2). Furthermore, the use of tracer flux techniques has indicated that the exchangeable fraction of intracellular potassium is 204 ± 14 mM. This represents the bulk of egg potassium (222 ± 19 mM as determined from flame photometry). Studies of unidirectional potassium efflux have indicated that its movement out of the egg is made up of at least two components; an external potassium-independent potassium efflux and external potassium-dependent efflux, the latter possibly representing a potassium exchange mechanism. The combined electrophysiological and tracer-flux data indicate that only a small portion of the total membrane conductance is composed of potassium conductance at this stage of development. This and the fact that the membrane potential is far from the potassium equilibrium potential are similar to observations made on mature eggs of several other species.     

Mechanism of the reaction catalyzed by carbamyl phosphate synthetase. Binding of ATP to the two functionally different ATP sites.

Application of the pulse-chase procedure to study of the binding and utilization of ATP by glutamine-dependent carbamyl phosphate synthetase from Escherichia coli showed that the enzyme binds the two molecules of ATP used in this reaction at the same time, and that the two ATP-binding sites are functionally different. Thus, ATP bound to the first ATP site is used for carboxy phosphate formation, and ATP bound to the second ATP site is used for phosphorylation of carbamate. The present and previous findings support a mechanism that involves intermediate formation of two highly unstable intermediates: carboxy phosphate and carbamate. It is proposed that the presence of all of the reactants on the enzyme at the start of the catalytic cycle allows immediate utilization of these labile compounds in the carbamyl phosphate synthesis reaction.