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KMID : 0358919990260020399
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Journal of the Korean Academy of Pedodontics
1999 Volume.26 No. 2 p.399 ~ p.415
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EFFECT OF OCTANOL, THE GAP JUNCTION BLOCKER, ON THE REGULATION OF FLUID SECRETION AND INTRACELLULAR CALCIUM CONCENTRATION IN SALIVARY ACINAR CELLS
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Abstract
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From bacteria to mammalian cells, one of the most important mediators of intracellular signal transduction mechanisms which regulate a variety of intracellular processes is free calcium. In salivary acinar cells, elevation of intracellular calcium concentration ((Ca´+)s) is essential for the salivary secretion induced by parasympathetic stimulation. However, in addition to (Ca2+)igap junctions which couple individual cells electrically and chemically have also been reported to regulate enzyme secretion in pancreatic acinar cells. Since the plasma membrane of salivary acinar cells has a high density of gap junctions, and these cells are electrically and chemically coupled with each other, gap junctions may modulate the secretory function of salivary glands. In this respect, I planned to investigate the role of gap junctions in the modulation of salivary secretion and (Ca2-) using mandibular salivary glands of rats.
In order to measure the salivary flow rate, fluid was collected from the cannulated duct of the isolated perfused rat mandibular glands at 2 min intervals. (Ca" )i was measured from the cells loaded with fura-2 by spectrofluorometry.
The results obtained were as follows
I. CCh-induced salivary secretion was reversibly inhibited by 1 mM octanol, a gap junction blocker.
2. CCh-induced increase in (Ca"+)i was also reversed by the application of 1 mM octanol.
3. Octanol did not block the initial increase in (Ca+)icaused by CCh, which suggested that the
reduction of (Ca+)i caused by gap junction blockade was not resulted from the inhibition of Ca"
release from intracellular Call stores.
4. Addition of octanol during stimulation with 1W thapsigargin, a potent microsomal ATPase inhibitor, reduced (Ca +)i to the basal level. This suggested that inhibition of gap junction permeability closed plasma membrane Ca" channels.
5. 2,5-di-tert-butyl-1,4 benzohydroquinone (TBQ) generated (Ca´+)i oscillations resulting from periodic influx of Ca´ via plasma membrane. The TBQ-induced (Ca2+)i oscillations were stopped by the application of 1mM octanol which implicated that gap junctions modulate the permeability of plasma membrane Ca´ channels.
6. Glycyrrhetinic acid, another well known gap junction blocker, also inhibited CCh-induced salivary secretion from rat mandibular glands.
These results suggested that gap junctions play an important role in the modulation of fluid secretion from the rat mandibular glands and this was probably due to the inhibition of Cat´- influx through the plasma membrane Cat´ channels.
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