Increase In Amylase Output Research Articles

Phosphorylation in vitro of proteins in the pancreas and parotids of rats: Effects of hormonal secretagogues and cyclic nucleotides

(1) Caerulein 10 −9 M and carbamylcholine 5·10 −6 M provoked a 3-fold increase in amylase secretion and a 50% stimulation of protein phosphorylation in rat pancreas fragments. Secretin exerted similar effects, though more moderate, at 5·10 −7 M concentration, but was inefficient at low concentrations. Dibutyryl-cyclic AMP 2 mM stimulated total protein phosphorylation (+28%) but the secretory effect was subdued (+50%). The effects observed with cyclic GMP and its dibutyrylated derivative were insignificant. (2) In rat parotids, 10 −5 M isoproterenol provoked a 10-fold increase in amylase output and exerted a slight (+15%) but significant effect on protein phosphorylation. These effects were reproduced by 0·5–2·0 mM dibutyryl-cyclic AMP. Dibutyryl-cyclic GMP at a high (5 mM) concentration allowed a slight increase (+86%) in enzyme secretion with no apparent stimulation of protein phosphorylation. (3) These results indicate a clear stimulation of protein phosphorylation when hormonal stimulus-secretion coupling was involved in the pancreas acinar cells and parotids. The derivatives of cyclic AMP partially mimicked these effects, and more clearly so in the parotids than in the pancreas.

Pancreatic acinar cells: acetylcholine-induced membrane depolarization, calcium efflux and amylase release.

1. The effects of acetylcholine upon the output of amylase, Ca(2+) efflux and membrane potential of pancreatic acinar cells have been measured in segments of mouse pancreas superfused in vitro.2. Amylase output was measured continuously using an on-line automated fluorimetric method; Ca(2+) efflux was monitored by measuring the release of (45)Ca(2+) from pre-labelled tissue; and intracellular recordings of acinar transmembrane potentials were obtained with glass micro-electrodes. In some experiments membrane potentials, and in others (45)Ca(2+) efflux, were measured concomitantly with amylase release.3. Acetylcholine depolarized the acinar cells, increased tissue (45)Ca(2+) efflux and raised amylase output, each with a similar dose-dependence, i.e. a maximal response at 10(-5)M, threshold =/< 10(-8)M, and ED(50) values of 0.7 x 10(-7)M, 0.5 x 10(-7)M, and 2 x 10(-7)M for depolarization, amylase release, and (45)Ca(2+) efflux, respectively.4. In response to acetylcholine both depolarization and (45)Ca(2+) efflux preceded or coincided with the increase in amylase output.5. Acetylcholine 10(-5)M and [K](0) 47 mM were without effect on (45)Ca(2+) efflux in the presence of atropine (3 x 10(-6)M) but pancreozymin (0.3 u./ml.) still elicited a marked increase in (45)Ca(2+) release.6. These results suggest that the stimulatory action of acetylcholine on the pancreatic acinar cell involves, sequentially, a specific receptor-activated increase in membrane permeability, depolarization, Ca(2+) mobilization and amylase release. These events are discussed in relation to the integrated mechanism of stimulus-secretion coupling.

Calcium-dependent amylase release and electrophysiological measurements in cells of the pancreas.

1. Transmembrane potential, effective membrane resistance, and amylase output were recorded from acinar cells of rat pancreas perfused in vitro.2. Both pancreozymin and acetylcholine hyperpolarized the acinar cells, increased effective membrane resistance, and augmented amylase output.3. The omission of calcium from the perfusion medium increased effective membrane resistance and potential, and abolished the increase in amylase output in response to the drugs.4. A quantitative relation was found between the amount of amylase released by pancreozymin and the concentration of calcium in the perfusion medium at values below the normal 2.5 mM calcium. Excess magnesium did not inhibit the increase in amylase output in response to the drug.5. It is concluded that the release of amylase from the pancreas depends on the entry of calcium into the acinar cells. The entry of calcium seems to be mediated by a carrier in the membrane and may be considered as a ;facilitated diffusion'.6. The electrophysiological findings taken together with morphological evidence provided by scanning electron microscopy favour the view that pancreatic zymogens are released from the granules in the acinar cells to the lumen by the process known as exocytosis.