Electron microscopical and histochemical studies of outer hair cells in acoustically exposed rabbits

After acoustic exposure, in the infranuclear region of the basal turn histochemically the lactate dehydrogenase activity increased more than normal. In the lower half of the second turn of this region, small vesicles, free ribosomes and coated vesicles decreased in number and cytoplasmic matrix become lower in electron density and lactic dehydrogenase activity decreased. Small vesicles were found to be preferentially distributed in the presynaptic side of the afferent nerve endings. Movement of these small vesicles leads to the speculation that small vesicles have close relationship to the afferent nerve endings.

Electron microscopical and histochemical studies of outer hair cells in normal rabbits

The outer hair cells of the rabbit were electron microscopically and histochemically investigated. The results clearly showed that the outer hair cells of the rabbit have no agglomeration of mitochondria in its infranuclear region. This anatomical fact means that the functional mechanism in the outer hair cells of the rabbit may be substantially different from that of other animals which have agglomeration of mitochondria. From the results of the histochemical study, it is reasonably supposed that the anaerobic energy metabolism may ordinarily play the leading part in sustaining the cellular functions in the infranuclear region of the outer hair cells of the rabbit.

Evaluation of succinyl neocarzinostatin in vivo

The toxicity of the bis-succinyl derivative of the protein antibiotic, neocarzinostatin, was compared with the parent compound, neocarzinostatin (NCS), in rats. The derivative was found to be about two to five fold more active than NCS in vivo. The antitumor activity in rats bearing eleven distinct Yoshida hepatoma ascitic cell lines was tested under four possible combinations with regard to sites of drug and tumor cell administration. The results indicate that the antitumor spectrum of the derivative had changed slightly. Antitumor activity in mice was also tested with L1210 and P388 lymphatic leukemia, and with B16 melanocarcinoma. When the effect of the derivative was compared with parental NCS at the molecular level with respect to the inhibition of DNA synthesis in vitro, the specific activities of the two were found to be almost identical. These results were interpreted to indicate that the succinyl derivative of NCS was more stable to inactivation and proteolytic break-down in vivo than NCS as observed previously in in vitro studies.

A detection method for lactic dehydrogenase activity in the inner ear

A method for the detection of lactic dehydrogenase enzymatic activity in outer hair cells of the rabbit is described. The membranous labyrinth with temporal bone was prefixed in glutaraldehyde. After being placed into the incubation medium, it was postfixed in osmium tetroxide. Specimens of the organ of Corti were removed. Then the specimens were embedded in water-soluble glycol and cut with a cryostat for light microscopy, and also they were embedded in Epon and cut for light and electron microscopy. Sectioning of the membranous labyrinth was very easily made when the specimens were embedded in both the water-soluble glycol and the Epon. The structures of the frozen sections as well as the Epon-embedded ones were well preserved. In the frozen sections the preservation and localization of reaction products were thoroughly kept, but monoformazan of the Epon-embedded sections was soluble.

Potentiation and its mechanism of cochlear damage resulting from furosemide and aminoglycoside antibiotics

The severe ototoxic interaction of the combined administration of furosemide and aminoglycoside antibiotics (kanamycin, streptomycin and gentamicin) was studied in rabbits, and its mechanism clarified. Severe damage occurred not only in the inner ear but also in the kidney when both furosemide and aminoglycoside antibiotics were administered to rabbits. Kanamycin concentration after a single injection of kanamycin with furosemide was much higher not only in the perilymph but also in the cerebrospinal fluid and serum than that after a single injection of kanamycin alone. The ototoxic interaction following the combined use of furosemide and aminoglycoside antibiotics seems to be caused mainly by the inhibitory effect of furosemide on the excretion of aminoglycoside antibiotics from the kidneys.

Isolation and purification of double-stranded ribonuclease from calf thymus

A RNase from calf thymus, which specifically cleaves native or synthetic double-stranded RNA molecules endonucleolytically, has been isolated and purified from calf thymus. For optimal activity, the enzyme requires a sulfhydryl reagent and divalent cations; over 95 per cent of the activity is inhibited by 0.5 mm ethidium bromide. The degradation of [3H]poly(C)-poly(I) by purified enzyme preparations yields labeled dinucleotides and octanucleotides; the latter oligonucleotide contained 5'-phosphate and 3'-hydroxyl termini. The enzyme cleaves high molecular weight RNAs such as RNA products formed in vitro by T3 phage-induced RNA polymerase from T3 phage DNA, heterogeneous RNA isolated from duck reticulocyte nuclei, and 45 S RNA isolated from rat liver nucleoli. The mode of degradation of RNA in vitro with the double-stranded RNase is similar to that of Escherichia coli RNase III and appears to act endonucleolytically. The degradation of 45 S RNA with the enzyme results in the production of 29 S and 19 S RNA fragments. These findings suggest that the enzyme may be involved in the processing of high molecular weight precursor RNAs to mRNA or rRNAs in a manner analogous to that reported for RNase III of E. coli.

Mechanism of DNA degradation induced by neocarzinostatin in Bacillus subtilis

When logarithmically growing Bacillus subtilis cells were exposed to the antitumor protein, neocarzinostatin (NCS), at a concentration of 50 mug/ml, cellular DNA was gradually degraded into an acid-soluble form (up to 60 percent of total DNA). The degradation appeared to initiate at the growing regions of DNA and to proceed sequentially from the nascent regions to preexistent DNA. Concomitantly with, or perhaps as a consequence of, the degradation of growing regions, DNA detached from the cell membrane and started to show single-strand nicks within 30 minutes after exposure of the cells to NCS, whereas double strand scission in the DNA became detectable in about 90 minutes. Such endonucleolytic breaks in DNA eventually gave rise to the formation of double-stranded DNA fragments of a single-size class (30-S) as determined by sedimentation in either neutral or alkaline sucrose gradients. In contrast to previous results with Sarcina lutea, the NCS-induced DNA degradation was stimulated by chloramphenicol in B. subtilis and the DNA fragment were not the final breakdown products, but were further degraded into acid-soluble materials.

Neocarzinostatin-induced breakdown of deoxyribonucleic acid in HeLa-S3 cells

Degradation of DNA in HeLa-S3 cells mediated by an acidic antitumor protein, neocarzinostatin (NCS), was examined. The concentration of NCS required for induction of DNA degradation was considerably higher than that which caused inhibition of DNA synthesis. Sedimentation analysis of DNA revealed that HeLa-S3 cell DNA first received single-strand nicks within 60 minutes after exposure to the antibiotic, whereas detectable double-strand scissions eventually gave rise to the accumulation of double-stranded DNA fragments of heterogeneous size. When the cells exposed to NCS were transferred to NCS-free medium at early stages of the degradation, the single-strand nicks caused in DNA were repaired by a process which was sensititive to puromycin.