Intracellular pH (pHi) was measured in the isolated, perfused rabbit mandibular salivary gland by 31P NMR spectroscopy. In the unstimulated gland perfused with HCO3-/CO2-buffered Ringer's solution, pHi was 7.27 +/- 0.01. Continuous stimulation with acetylcholine elicited dose- and time-dependent changes in pHi. 10(-6) mol/l acetylcholine caused a brief intracellular acidosis (-0.19 +/- 0.06 pH units) followed by an increase in pHi to a more alkaline steady-state value (7.33 +/- 0.02). In the absence of perfusate HCO3- or in the presence of 10(-4) mol/l DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid), the transient acidosis was abolished and pHi increased rapidly to give a sustained alkalosis (7.49 +/- 0.03 and 7.44 +/- 0.03 respectively). In the presence of 10(-3) mol/l amiloride, the response to acetylcholine was a rapid decrease in pHi to 7.02 +/- 0.02. The data suggest that, during perfusion with HCO3-/CO2- buffered solutions, stimulation with acetylcholine results in a transient loss of HCO3- from the acinar cells (causing a transient acidosis), and, independently, the activation of Na+-H+ exchange (causing a sustained alkalosis). In the unstimulated gland, DIDS and the HCO3- -free perfusate caused decreases in pHi to 7.12 +/- 0.02 and 7.04 +/- 0.01 respectively. In contrast, amiloride had little effect. The relatively high value of pHi maintained by the unstimulated gland is therefore probably not due to Na+-H+ exchange.
SUMMARYOsmotic stress was applied to the perfused rat submandibular gland during steady-state fluid secretion. Alterations of perfusate osmolarity, by addition or withdrawal of sucrose or NaCi, caused transient changes in secretory rate during continuous stimulation with I /LM acetylcholine (ACh). Hyposmotic perfusates transiently increased, and hyperosmotic perfusates transiently reduced, the secretory rate. The transients were attributed to changes in osmotic flow resulting from changes in the instantaneous transepithelial osmotic gradient. The time course of the change in interstitial osmolarity was determined by using a Cl-electrode to record the changes in interstitial Cl-concentration following a step change in perfusate Cl-concentration. From the calculated changes in interstitial osmolarity and the resulting changes in secretory rate, the osmotic
Epithelia are responsible for the directional transport of selected materials to and from the external environment: absorption involves transport into the epithelial cell across the apical (luminal) cell membrane, followed by exit across Abbreviations used: BCECF, 2',7'-bis(carboxyethyl)-5(6')carboxyfluorescein; ACh, acetylcholine; DIDS, 4,4'-di-isothio-
322.273-286256, C28X-C295
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