A complex aggregation of microorganisms growing on a solid substrate is termed a biofilm and is considered to be an etiological agents. Pseudomonas aeruginosa and Streptococcus mutans are representative bacteria in such biofilms. It is well known that deuterium oxide (D 2 O) causes toxic effects on a number of biological systems. We investigated the effects of D 2 O on growth and biofilm formation of P. aeruginosa and S. mutans. These bacteria were incubated in medium containing D 2 O (100%, 75% or 0%) at 37°C for 24hr, 48 hr or 72hr. Growth of P. aeruginosa was inhibited by D 2 O within the first 48hr. However, after 72 hr, growth rate was seen to increase in the D 2 O-containing medium compared with in medium without D 2 O. In contrast, the growth of S. mutans in the D 2 O medium was inhibited within 72hr. The biofilm formation of P. aeruginosa was increased in the D 2 O medium. Biofilm formation of S. mutans in the D 2 O medium increased compared with in the medium without D 2 O, but this increase was only temporary in the case of P. aeruginosa. Compared to biofilm formation in 0% D 2 O medium marked as 100%, the biofilm formation rate of S. mutans in 75% D 2 O medium was 143% at 24hr, 146% at 48 hr and 130% at 72 hr. In other D 2 O concentration media biofilm formation was lower. In 100% D 2 O medium, biofilm formation rate decreased from 114% at 24hr to 56% at 72hr. The biofilm formation rate of P. aeruginosa in 100% D 2 O medium was 172% at 24hr, but decreased to 88% at 72hr. Biofilm formation of P. aeruginosa in 75% and 0% D 2 O media showed no significant difference. We consider that these results were due to stress or alteration in bacterial metabolisms.
Guanylyl cyclase activity was cytochemically demonstrated in rabbit foliate taste buds. The enzymatic activity was localized in the apical portion (microvilli and neck) of taste bud cells. Especially strong activity was observed on the microvillous membrane of type I (dark) cells and often on a blunt process of type III cells. The microvilli of type II (light) cells showed weak enzymatic activity. Considering that the apical portion of taste cells is a likely site of interaction between taste stimuli and the cells, the results support the idea that cyclic GMP is involved in taste transduction.
Adenylate cyclase activity was demonstrated in the cilia, dendritic knob and axon of rat olfactory cells by using a strontium-based cytochemical method. The activity in the cilia and the dendritic knob was enhanced by non-hydrolyzable GTP (guanosine triphosphate) analogues and forskolin, and inhibited by Ca2+, all in agreement with biochemical reports of the odorant-sensitive adenylate cyclase. The results support the hypothesis of cyclic AMP working as a second messenger in olfactory transduction and imply that the transduction sites exist not only in the olfactory cilia but also in the dendritic knob. Enzymatic activity was also observed in the olfactory dendritic shaft by treating the tissue with 0.0002% Triton X-100, although the properties and role of the enzyme in this region are uncertain. The detergent inhibited the enzymatic activity in the cilia and the dendritic knob.
Using the newly designed test materials, counting the number of chewing strokes necessary for recognizing the taste would be a useful index of a new gustatory test to investigate taste sensation.
Cyclic 3',5'-nucleotide phosphodiesterase activity was demonstrated cytochemically in the rat olfactory mucosa using cyclic AMP as substrate. Strong activity was observed on the plasma membrane of the cilia, dendritic knob and axon of olfactory cells; weak activity was apparent on the membrane of the dendritic shaft and cell body. This suggests that the cyclic AMP produced by odorant-sensitive adenylate cyclase in the dendritic terminal acts mainly in its original site and to a lesser extent in the dendritic shaft and cell body. The enzyme also hydrolysed cyclic GMP but the hydrolysis was not as great as in the case of cyclic AMP. Besides its presence in olfactory cells, enzymatic activity was also observed on the plasma membrane of basal cells and certain supporting cells with an astrocyte-like morphology.
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