Effects of Ion Transport Inhibition on Rat Mandibular Gland Secretion

Abstract

The effects of substituting gluconate for extracellular Cl, and of treatment with various ion transport blockers, on cytosol pH (pHi) and secretion by the acetylcholine stimulated rat mandibular gland were studied in vitro. Gluconate replacement increased pHi from 7.12 +/- 0.02 to 7.27 +/- 0.04, caused secretory rate to fall by 75%, and increased salivary HCO3 from 14 +/- 0.9 mmol/L to 67 +/- 1.5 mmol/L. Furosemide (1 mmol/L), which blocks Na-K-2Cl symports and Cl-HCO3 antiports, had effects similar to those of gluconate replacement, except that secretion was reduced only by 59%. Bumetanide (1 mmol/L), which blocks only Na-K-2Cl symports, caused a 67% reduction in secretion rate, but it had little effect on pHi and caused only a small rise in salivary HCO3 concentration. SITS (1 mmol/L), which blocks Cl-HCO3 antiports, increased pHi to 7.26 +/- 0.03 and induced a small rise in the secretory rate. Methazolamide and acetazolamide (1 mmol/L), both of which inhibit carbonic anhydrase and may also block anion channels, increased pHi to 7.43 +/- 0.02 and 7.20 +/- 0.03, respectively, but had no effect on secretory rate, and reduced salivary HCO3 slightly. Ba (3 mmol/L), tetraethylammonium (10 mmol/L), and decamethonium (5 mmol/L) all caused marked but reversible reductions in secretory rate, consistent with the known actions of these agents on K channels. Ba, however, also appeared to act as a Ca antagonist, an action that it seemed to share with Mn ions (5 mmol/L).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological investigation of the role of ion channels in salivary secretion

“…This indicates a role for K + channels sensitive to Ba 2+ in the millimolar range. That Ba 2+ inhibits AChinduced secretion is in agreement with previous vascular perfusion experiments on rabbit and rat submandibular glands [18,23,44]. In all studies, including the present, Ba 2+ has a relatively modest inhibitory effect on salivary secretion.…”

“…5B). The strong inhibitory effect obtained with 50 M bumetanide correlates well with previous perfusion studies [23,44], corroborating the involvement of the Na + -K + -2Cl cotransporter in secretion and validating the method employed in the present study. Calibration bar in A applies to all panels.…”

“…The 125 I-IbTX-D19Y/Y36F binding parameters found in the present study show high expression of BK channels in the glands as the expression level is similar to that of distal colon surface and urinary bladder [8,28], other non-excitable tissues with high BK channel expression, and to that of brain membranes [22], where a high density of channels is expected (see Table 1 for B max and K d values). As described in the Introduction, BK channels [26,31,32,37,43,44], no quantitative data on BK channels are available, the present study thus documents the number of BK channels for the first time.…”

“…Patch-clamp experiments have demonstrated the presence of Ca 2+ -and voltageactivated BK channels in rat parotid as well as mouse parotid and submandibular acinar cells [26]. These channels were considered obvious candidates for the K + channels activated during secretion, an idea supported by other patch-clamp studies on human and sheep parotid acinar cells [32,43], flux studies on rat parotid acinar cells [31,37] and vascular perfusion experiments on rat submandibular glands [44]. In contrast, other perfusion studies on rat submandibular glands [18] and patch-clamp studies on mouse submandibular and sheep, rat and mouse parotid acinar cells do not support the involvement of BK channels in formation of saliva [12,13,14].…”

Cellular Mechanisms Underlying the Production of Primary Secretory Fluid in Salivary Glands

“…The simplest explanation of these findings is that salivary cells possess a Na/H antiport which is unmasked when the Na, K, 2C1 symport is inhibited. This view is supported by the observation that the residual secretion is blocked by amiloride 84 and by recent observations that amiloride inhibits the uptake of 22 Na in rat submandibular acini. 53 As secretion is not affected by removal of external HCO 3 or by exposure to carbonic anhydrase inhibitors (see earlier discussion), the system is likely to be more complex than one consisting of a Na/H antiport alone.…”