Characteristics of fluid secretion from isolated rat pancreatic ducts stimulated with secretin and bombesin.

Abstract

SUMMARY1. Micropuncture techniques were used to study the cellular mechanisms of fluid secretion by interlobular ducts isolated from the pancreas of copper-deficient rats.2. Perifusing ducts with a calcium-free buffer containing 5 mM-EGTA reduced the volume of fluid secreted in the presence of 10 nM-bombesin by 62 %, whereas fluid secretion measured in the presence of 10 nM-secretin was reduced by only 26 %. 4. SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid; mM), reduced fluid secretion measured in the presence of bombesin by 61 %, but had no effect on the response to secretin. 5. The K+ channel blockers, barium (3 mM) and tetraethylammonium (TEA; 10 mM), inhibited fluid secretion measured in the presence of both secretin and bombesin by between 52 and 66%.6. From these results, we conclude that secretin and bombesin may utilize different intracellular signalling pathways and, furthermore, may activate different anion secretory mechanisms within the pancreatic ductal epithelium. However, the effect of the potassium channel blockers is consistent with both peptides activating secretory mechanisms which are electrogenic, and which depend for their operation on potassium efflux across the basolateral membrane of the duct cell.

Regulation of fluid secretion and intracellular messengers in isolated rat pancreatic ducts by acetylcholine.

“…Previously, we have shown that secretin and bombesin are potent stimulants of fluid secretion from isolated pancreatic ducts Ashton et al 1991), whereas substance P acts as an inhibitor ). We therefore tested the effect of these substances on duct cell [Ca2+]i and found that neither secretin (10 nm, six ducts), bombesin (10 nm to 1 /UM, ten ducts) nor substance P (0-1-1 fM, nine ducts) had any effect on this parameter, although the same ducts responded to ACh.…”

“…If, as we believe, most of this chloride-rich fluid originates from the ducts (see above), then the ductal epithelium must be capable of switching from HCO3-to Cl-secretion depending on the type of stimulant to which it has been exposed. Previously, we have speculated that this switch could be achieved by moving one of the transport elements located in the duct cell (a Cl--HCO3-exchanger) from the apical to the basolateral plasma membrane (Ashton et al 1991). …”

“…However, we have recently challenged the idea that acinar and ductal functions are under separate control by showing that fluid secretion from isolated rat pancreatic ducts can be stimulated by bombesin and inhibited by substance P (Ashton, Argent & Green, 1990, 1991, two agents which were previously thought to act only on acinar cells.…”

“…Ductal fluid secretion was measured using micropuncture techniques as previously described Ashton et al 1990;Ashton et al 1991). In brief, ducts were immobilized in a ISOLATED PANCREATIC DUCTS perifusion bath (volume 5 ml) using a suction pipette, and then micropunctured with a bevelled, oil-filled, collection pipette.…”

Secretin

“…Latter studies isolated ducts by microdissection from pancreas of rats, guinea pigs, and mice partially digested with collagenase. Secretin has been shown to stimulate bicarbonate fluid in the isolated duct fragments by microperfusion and by letting the ends of the ducts seal in culture after which the volume increase can be monitored by video microscopy and the ion content sampled by micropuncture (3,34,46). Guinea pig ducts have been especially useful because they secrete a high concentration of bicarbonate similar to humans while rats and mice secrete lower amounts (100).…”