Evidence for Bicarbonate Secretion by Ameloblasts in a Novel Cellular Model

Formation and growth of hydroxyapatite crystals during amelogenesis generate a large number of protons that must be neutralized, presumably by HCO3 (-)ions transported from ameloblasts into the developing enamel matrix. Ameloblasts express a number of transporters and channels known to be involved in HCO3 (-)transport in other epithelia. However, to date, there is no functional evidence for HCO3 (-)transport in these cells. To address questions related to HCO3 (-)export from ameloblasts, we have developed a polarized 2-dimensional culture system for HAT-7 cells, a rat cell line of ameloblast origin. HAT-7 cells were seeded onto Transwell permeable filters. Transepithelial resistance was measured as a function of time, and the expression of transporters and tight junction proteins was investigated by conventional and quantitative reverse transcription polymerase chain reaction. Intracellular pH regulation and HCO3 (-)transport were assessed by microfluorometry. HAT-7 cells formed epithelial layers with measureable transepithelial resistance on Transwell permeable supports and expressed claudin-1, claudin-4, and claudin-8-key proteins for tight junction formation. Transport proteins previously described in maturation ameloblasts were also present in HAT-7 cells. Microfluorometry showed that the HAT-7 cells were polarized with a high apical membrane CO2 permeability and vigorous basolateral HCO3 (-)uptake, which was sensitive to Na(+)withdrawal, to the carbonic anhydrase inhibitor acetazolamide and to H2DIDS inhibition. Measurements of transepithelial HCO3 (-)transport showed a marked increase in response to Ca(2+)- and cAMP-mobilizing stimuli. Collectively, 2-dimensional HAT-7 cell cultures on permeable supports 1) form tight junctions, 2) express typical tight junction proteins and electrolyte transporters, 3) are functionally polarized, and 4) can accumulate HCO3 (-)ions from the basolateral side and secrete them at the apical membrane. These studies provide evidence for a regulated, vectorial, basolateral-to-apical bicarbonate transport in polarized HAT-7 cells. We therefore propose that the HAT-7 cell line is a useful functional model for studying electrolyte transport by ameloblasts.

Role of nitric oxide in the regulation of blood flow in the rat submandibular gland during carotid artery occlusion

The possible involvement of nitric oxide in the preservation of blood flow to the rat submandibular gland after uni- or bilateral occlusion of the common carotid was studied. Glandular blood flow and mean blood pressure were monitored before, during and after carotid occlusion in the presence and absence of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine-methyl-ester (L-NAME). To calculate vascular resistance, the local perfusion pressure distal to the point of occlusion was also measured. In normal rats, uni- or bilateral carotid occlusion resulted in an immediate decrease in ipsilateral glandular blood flow. After the cessation of carotid occlusion, hyperaemia was observed in the submandibular gland. Both local perfusion pressure and vascular resistance decreased during carotid occlusion. In the group pretreated with L-NAME, trends in blood-flow responses to uni- or bilateral occlusion were identical to those registered in the control groups, though the magnitude of the alterations was significantly less. The well-maintained glandular blood flow was due to functioning vascular anastomoses and compensating dilatation of glandular blood vessels. Nitric oxide had only a restrained effect on this compensatory mechanism.

[Blood flow in marginal gingiva as measured with laser Doppler flowmetry]

The clinical application of laser Doppler flowmetry (LDF) provides data on the blood flow of marginal gingiva (GBF) at different dental regions. The aim of the present investigation was to study the GBF at different teeth. Ten adult subjects with good oral hygiene were involved in this experiment. In a series of experiments GBF was recorded bilaterally positioned the flow probe on three sites 1 mm above the marginal gingiva of the upper and lower central incisors. In another series of investigations the same technique was used for GBF registrations at six permanent teeth on the right side (11-16; according to FDI notation). The mean blood flow values obtained at 3 different places of marginal gingiva of the front teeth were nearly identical, therefore the data were pooled. The GBF values registered at the six upper right teeth also showed close similarity (p > 0.30). No differences were observed between the mean GBF values at the left and right central incisors (p > 0.80). There was a significant gingival blood flow value elevation at lower incisors as compared to that in the upper jaw (p < 0.05). Our results indicate that there is homogeneous marginal blood perfusion both in the maxillary and mandibula healthy gingiva. However, difference exists in blood supply between the upper and lower jaws in favor of mandibular marginal gingiva.

[Blood flow measurements in human oral tissues with laser Doppler flowmetry]

In our examination the non-invasive laser Doppler flowmetry (LDF) was used to determine the blood flow in the tooth pulp (PBF) and in the gingiva (GBF) in humans. Perfusion values were collected by the means of LDF probe adjusted manually or by manipulator assisted fixation. Significantly lower GBF rate was detected by hand-held probe as compared to that obtained by manipulator assisted fixation (p < 0.001). No significant difference was observed for the PBF rates (p > 0.9). The coefficient of variation determined for GBF was higher (0.32 +/- 0.09) in case of manual procedure than at manipulator assisted (0.13 +/- 0.02) fixation mode. In contrary, the value of variation coefficient of PBF data obtained by hand-held probe was lower as compared to that calculated from data of manipulator fixation (0.16 +/- 0.08 v. 0.22 +/- 0.1; p < 0.05). These data indicate that while the manual fixation for measuring PBF seems to be satisfactory, for the accurate determination of GBF rate application of manipulator is essential.