Observations on the potassium-induced contraction of single muscle fibers from depressor mandibulae muscle showed them to be fast fibers. This confirms the hypothesis formulated earlier by electron microscopy. The K⁺ concentration versus tension curve showed that each fiber could be classified into one of 3 groups according to the K⁺ concentrations (20, 30 and 50 mM) required for one half-maximum tension development and the threshold of tension. Their contractile activation and inactivation response to K⁺-depolarization varied according to this classification; thus, the contractile response of the more K⁺-sensitive groups was more rapid. Thus, the fibers were distributed as follows: high K⁺ sensitivity group, 51%(n=19), moderate group, 38%(n=14), and low group, 11%(n=4). Further, under the condition of Ringer's fluid at pH 5.6, the K⁺ concentration versus tension curve shifted to the right.
Caffeine-induced contractions that do not depend on a change of membrane potential were the same in the 3 groups. This result indicates that there exists no difference in the contraction process among the three groups after the release of Ca²⁺ from terminal cisternae. In addition, there is no difference in the diffusion of K⁺ Ringer among the three groups, because they have the same shape, including the T-tubule. These results suggest that the mechanism that causes the difference in K⁺ sensitivity exists between the T-tubule and terminal cisternae, which is the site of E-C coupling.
Electron microscopy, however, did not reveal any morphologic difference that would explain the difference in K⁺-sensitivity among the 3 groups. Therefore, the variation in K⁺-sensitivity is due to a molecular difference in the mechanism of E-C coupling between T-tubules and terminal cisternae.
It is reported that the digastric muscle of mammals, which is homologous to the depressor mandibulae muscle of the present animal, R. japonica, has characteristically few muscle spindles. It follows, then, that movement control by the digastric muscle should proceed without the muscle spindle. This is probably the case also in the frog depressor mandibulae muscle, and the described differences in K⁺-sensitivity may help regulate movement of the depressor mandibulae muscle.

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This study was designed to determine whether the submandibular glands of rats subjected to chemical sympathectomy with reserpine administration showed abnormalities in five types of receptor functions, and to determine whether tyramine acted as a false neurotransmitter.
The wet tissue weights of the submandibular glands of rats significantly increased one and two days after chemical sympathectomy with reserpine. Supersensitivities of fluid and protein secretion in response to isoproterenol, noradrenaline, clonidine and physalaemin were clearly seen in the reserpine-treated animals when compared with those of controls. In particular, supersensitivity to noradrenaline occurred in fluid and protein secretion in the reserpine-treated animals. The β-type proteins secreted in controls in response to noradrenaline at a low dose (1 mg/kg) were completely replaced by the α-type proteins in reserpine-treated animals. Tyramine was a completely false neurotransmitter. This study suggests that almost complete release of noradrenaline from the sympathetic nerve terminals could occur in the submandibular glands of rats treated with reserpine according to this protocol, and that released noradrenaline could potentiate the α-type protein secretion by the granular duct cells of the submandibular glands of rats.

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The mechanisms underlying the responses of the canine lingual artery to bradykinin (BK) have been examined. In endothelium-intact lingual artery ring preparations contracted to a stable plateau tension by the addition of norepinephrine (NE), BK produced B2-receptor antagonist [D-Phe⁷]-BK-sensitive and endothelium-dependent relaxations. Theobserved effect was significantly inhibited by nitric oxide (NO) inactivator hemoglobin, methylene blue, a good inhibitor of soluble guanylate cyclase, and by N^G-monomethyl-L-arginine, a NO synthase inhibitor, but not by B₁-receptor antagonist des-Arg⁹-[Leu⁸]-BK, suggesting endothelial production of the vasodilator agent NO by B₂-receptors activation. In endotheliumdenuded rings in the absence of active tension caused by NE, BK increased muscle tension and cytosolic Ca²⁺ level; these were inhibited by [D-Phe⁷]-BK. The concentration-dependent contraction produced by BK of endothelium-denuded rings was also attenuated by [D-Phe⁷]-BK; protein kinase C inhibitor H-7 and phospholipase C inhibitor neomycin B reduced the BK-induced contraction. Indomethacin was without effect. Hence, it can be concluded that BK can cause relaxation and contraction in the canine lingual artery via B₂-receptors activation. The relaxation response to BK might be mediated by endothelial production of No.BK has the potential to be a vasoconstrictor by exerting an effect on vascular smooth muscle cells, but not on endothelial cells, via B₂-receptors activation. It is also postulated that the contractile response to BK may be due to the production of second messengers derived from the action of phospholipase C, but not due to contractile prostanoids, when B₂-receptors are activated.

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The purpose of this study is to investigate heterogenous cell populations in cultured rat periodontal ligament (PDL) cells and to isolate different cell populations from PDL cells. Outgrowing rat PDL cells obtained from the mandibular incisors were cultured for 24 days and alteration of cells was observed. A few foci appeared in the culture on day 8 and they enlarged. The cells in the foci expressed osteocalcin (Osc) by immunohistochemistry, and they formed mineralized nodules on day 24, but the cells from the surrounding area did not. Osc production from the cells by immunoassay was closely related to enlargement of the foci. The cells cultured on thin membranes were isolated on day 18 by inserting fine-point pasteur pipets into the center of each focus and the surrounding area under the dissecting microscope. Most of the cells isolated from the focus expressed Osc protein and mRNA, while the cells isolated from the surounding area expressed neither Osc protein nor mRNA. These Osc-expressing or non-expressing cell populations would be useful to investigate the precise biological function and inte raction between different cell populations of PDL cells.

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Stress-strain curves of the periodontal ligament obtained by pulling a tooth part out of its alveolar bone in transverse sections of impeded and unimpeded rat mandibular incisors at low velocities (0.5mm/24h or 1.0mm/24 h) were analysed. The maximum shear stresses were always greater in the impeded than in the unimpeded incisors at the same loading velocity and the rate of increase in the maximum shear stress in association with increases in loading velocity were also greater in the impeded than in the unimpeded incisors. The tangent moduli and failure strain energy densities also showed similar tende ncies. Light and scanning electron microscopic observations showed that the periodontal ligament was sheared in its middle layer when loaded at either 0.5 or 1.0mm/24 h, and that the free surfaces of the sheared ligament were rather smooth with the fibres running mostly parallel to the long axis of the tooth. These results suggest that the periodontal ligament of the rat incisor could generate a variable resisting force according to the velocity of tooth movement, and thus automatically regulate the rate of tooth eruption. Sliding of the periodontal fibre bundles occurs in the middle layer of the ligament when loaded at approximate rates of eruption.

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Compound action potentials (CAP) in response to orthodromic stimulation of the nerve trunk were extracellularly recorded from bullfrog sympathetic ganglia. Application of pentobarbital (PB) significantly suppressed the CAP-amplitude. The mode of inhibition of PB on the synaptic transmission was apparently competitive when examined under the condition of lowered transmitter release by low Ca²⁺-solutions and analyzed by dose-inhibition curves. However, the mode of inhibition by PB was noncompetitive when examined under increased transmitter release by 3, 4-diaminopyridine (3, 4-DAP). Furthermore, acetylcholine (ACh)-induced depolarizing response, intracellularly recorded from a sympathetic ganglion cell, was markedly suppressed by PB. The mode of inhibition by PB on the ACh-induced response was noncompetitive when analyzed in low Ca²⁺-solutions. These results suggest that PB suppresses both of the transmitter release from the presynaptic terminal and ACh -receptor activation at the postsynaptic membrane, and that the latter effect of PB is dominant in normal Ringer's soluti on to suppress the synaptic transmission at the sympathetic ganglia.

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Immunolocalization of enamelprotein in secretory ameloblasts (SA) before and after treatment with Brefeldin A (BFA) was done in 12 day-cultured mouse molar tooth germs using a polyclonal antibody which cross reacted with both amelogenin and enamelin.
Tooth germs from 16.5-day-old mouse embryos (vaginal plague day 0) were cultured in an organ culture system using BGJb culture medium, supplemented with 10% FCS, 2 mM Glutamine, 2 mM Glysine and 0.5 mM Vitamin C. In the experimental group, on culture day 12, BFA was introduced to whole tooth germs in the culture medium for different periods of time. For the control group, tooth germs were sampled at time zero, before treatment with BFA. The tooth germs treated with and without BFA were fixed for ultrastructural and immunohistochemical observations.
BFA treatment caused vesiculation of the Golgi lamellae following the disassembly of the Golgi complex, distention of the cisternae of the rER, in which accumulation of fine granular material was observed, and the disappearance of secretory granules in the Tomes' processes. Immunolabeling of the fine granular material which was observed in the distended cisternae of the rER, in the secretory ameloblasts treated with BFA, proves that the accumulated material is enamel protein, therefore confirming that enamel protein is processed in the rER.
In BFA untreated secretory ameloblasts, labeling was observed in the enamel matrix, Golgi complex, and secretory vesicles. No labeling was observed in the rER.

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Mechanisms of sweet taste transduction in gerbil taste cells were examined using the conventional whole-cell patch-clamp technique. Outward K⁺ currents of the taste cell induced by depolarizing electric pulses were reduced by 10 mM Na-saccharin, but were enhanced by amino acid sweeteners of 10 mM D-tryptophan. The outward K⁺ current was also enhanced by external application of Ca²⁺ -ionophore, 5μM ionomycin and intracelluar application of 5μM IP₃, (inositol-1, 4, 5-trisphosphate). These results suggest that the sweet taste transduction mechanism for Na-saccharin is concerned with an increase of the intracellular cAMP level, while that for D-tryptophan is concerned with an increase of the intracellular IP₃, level causing Ca₂₊ release from the internal stores. Gurmarin, an inhibitor of sweet taste. antagonized the suppressive effect of Na-saccharin on outward K⁺ currents, but did not affect the enhancing effect of Dtryptophan on outward K⁺ currents. The results from treatment with gurmarin suggest that the receptor site for Na-saccharin is different from that for D-tryptophan.

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