抄録
Intercellular canaliculi (IC) is a primary mixing reservoir for transcellularly and paracellularly secreted saliva whose composition is dependent on the degree of elevation of cytosolic Ca2+ and of cytosolic cyclic AMP concentrations caused by various secretagogues. In rat submandibular gland (SMG), appearance of exocytosis on IC reflected the amount of secreted mucin (Murakami 2002). Segawa (2002) showed in the parotid gland (PG) that, while at first transcellular fluid secretion predominates subsequently there is an increase of paracellular fluid transport through the tight junctions. By contrast, vigorous secretory stimulation at higher concentration of carbachol (1μM CCh) and isoproterenol (1μM ISP) caused enormous deformation of IC and decrease in ATP (Murakami 2002). The present morphological observation was carried out by HR-SEM using a modified osmium maceration method (Riva 1994) on specimens treated with CCh and/or ISP. Mild secretory stimulation revealed that exocytosis did not occur simultaneously even along the same intercellular canaliculus. Higher dose did not change the spatial distribution but increased the frequency of exocytosis. The temporal frequency of exocytosis along intercellular canaliculi was dose-dependent. These findings lead to conclude that under low level of secretory stimulation exocytosis does not show a dose-dependent change, but that its spatial and temporal frequency changes dose-dependently. [Jpn J Physiol 54 Suppl:S88 (2004)]
