Activation of contraction by voltage-clamped stimulation in crayfish muscle fibers (author's transl)

It is known that the properties of the excitation-contraction coupling of crayfish skeletal muscle are different in some respects from those of frog muscle. In the present study, activation of contraction of the crayfish muscle induced by short depolarizing pulses was investigated and it was compared with the results of frog muscle obtained by Adrian, Chandler and Hodgkin (1969). Two glass microelectrodes were inserted into the thoracal muscle of the crayfish. The muscle was stimulated by the voltage-clamped pulses of different durations and the resulting contractions were observed under the binocular microscope with the magnification of 60 X at 20 approximately 23 degrees C. The rheobasic membrane potential was -55mV. The mechanical threshold potential was -42 mV for 10 msec, -15 mV for 2.5 msec, +18 mV for 1 msec and around +90 mV for 0.5 msec pulses. For short pulses where the threshold potential was more positive than -20 mV, the area of the depolarization above -30 mV was 51 mV-msec. Subthreshold pulses produced contraction if applied repetitively. The effect of a just suprathreshold short pulse on the activation of contraction was cancelled by the hyperpolarizing pulse.     

Carotenoid synthesis in Streptomyces setonii ISP5395 is induced by the gene crtS,whose product is similar to a sigma factor

In many species of actinomycetes, carotenogenesis can be photoinduced. The capacity to respond to photoinduction is, however unstable and, in various strains of Streptomyces, is lost at a relatively high frequency. In Streptomyces setonii ISP5395, which normally produces no carotenoids, carotenoid-producing mutants can be obtained following protoplast regeneration. We report here the characterization of a gene, crtS, which was isolated from one such mutant and can confer on wild-type S. setonii ISP5395 cells the capacity to synthesize carotenoids. Sequence analysis of crtS reveals an open reading frame, which shows homology to genes that encode alternative sigma factors in Bacillus subtilis. We propose that crtS encodes a sigma factor which is necessary for the expression of a cryptic gene(s) for carotenoid biosynthesis in S. setonii ISP5395.     

Oral administration of l-citrulline alters the vascular delivery of substances to rat skeletal muscles

Vascular endothelial function deteriorates with age and disease, and the production of vasodilator factors like nitric oxide (NO) decreases. The free amino acid l-citrulline increases vasodilation and blood flow through increased NO production. We examined the effects of oral l-citrulline administration on vascular delivery of substances to skeletal muscles. In Experiment 1, following oral l-citrulline administration and subsequent intravenous Evans blue dye (EBD) administration to rats, EBD levels delivered to skeletal muscles were measured after 60 min. In Experiment 2, plasma concentrations of amino acids and NOx, an indicator of vasodilation, were measured over time after oral l-citrulline administration. In Experiment 3, we measured EBD levels in skeletal muscles of streptozotocin-induced type 1 diabetic rats following l-citrulline administration. In these experiments, EBD levels in the soleus muscle were higher in the l-citrulline group than in the control group (19.9 ± 0.7 vs. 22.5 ± 1.9 μg/g tissue, p < 0.05). Plasma l-arginine, l-citrulline, and NOx levels were increased within 30 min after l-citrulline administration. EBD levels in the soleus and gastrocnemius muscles were higher in diabetic rats with l-citrulline administration (18.7 ± 2.2 vs. 25.0 ± 4.3 μg/g tissue, p < 0.05 and 8.0 ± 0.5 vs. 9.2 ± 0.8 μg/g tissue, p = 0.05, respectively). These data suggest that oral l-citrulline administration may increase the level of substances delivered to skeletal muscles by increasing the NO production in both normal and vascular endothelial dysfunction models.     

Comparison of autophagy inducibility in various tyrosine kinase inhibitors and their enhanced cytotoxicity via inhibition of autophagy in cancer cells in combined treatment with azithromycin

Tyrosine kinase inhibitors (TKIs) induce autophagy in many types of cancer cells. We previously reported that gefitinib (GEF) and imatinib (IMA) induce autophagy in epidermal growth factor receptor (EGFR) knock-out A549 and non-BCR-ABL-expressing leukemia cell lines, respectively. This evidence suggests that TKI-induced autophagy is independent of the original target molecules. The present study compared the autophagy-inducing abilities of various TKIs, regardless of their targets, by quantitative autophagy flux assay. We established stable clones expressing the GFP-LC3-mCherry-LC3ΔG plasmid in A549, PC-9, and CAL 27 cell lines and assessed autophagy inducibility by monitoring the fluorescent ratios of GFP-LC3 to mCherry-LC3ΔG using an IncuCyte live cell imaging system during exposure to TKIs viz; GEF, osimertinib (OSI), lapatinib (LAP), lenvatinib (LEN), sorafenib (SOR), IMA, dasatinib (DAS), and tivantinib (TIV). Among these TKIs, DAS, GEF, and SOR exhibited prominent autophagy induction in A549 and PC-9 cells. In CAL 27 cells, IMA, SOR, and LEN, but not GEF, TIV, or OSI, exhibited autophagy induction. In the presence of azithromycin (AZM), which showed an inhibitory effect on autophagy flux, TKIs with prominent autophagy inducibility exhibited enhanced cytotoxicity via non-apoptotic cell death relative to effects of TKI alone. Therefore, autophagy inducibility of TKIs differed in the context of cancer cells. However, once induced, they appeared to have cytoprotective functions. Thus, blocking TKI-induced autophagy with AZM may improve the therapeutic effect of TKIs in cancer cells.     

Alternative male mating behaviors in landlocked Dolly Varden (Salvelinus malma) in south-central Alaska

Mating in Dolly Vardens (Salvelinus malma) was studied in relation to individuals' dominance ranks in a landlocked population in south-central Alaska. Two types of tactics were adopted by males: pairing directly with a spawning female and streaking to a spawning pair. Average success in sperm release was 97% in pairing but only 47% in streaking, and depended on the distance to the female. The pairing tactic was mostly monopolized by males of primary and secondary dominance rank. These dominant males were the largest (≥210 mm in fork length) and the oldest (≥6 years) individuals. Their mating success per season was much higher than that of the smaller and younger males.