Amylase release from dissociated mouse pancreatic acinar cells stimulated by glucagon: effect of membrane stabilizers.

Abstract

SUMMARY1. The effect of membrane stabilizers and cytochalasin-B on amylase secretion, basal and induced by ionophore A23187, CCK-PZ, bethanechol and glucagon, was studied in dissociated mouse pancreatic acinar cells.2. Cytochalasin-B did not affect basal or secretagogue-stimulated amylase secretion.3. Membrane stabilizers [thymol (10-7-104 M), chlorpromazine (I0-7-1 04 M) and propranolol (10-7-10-5 M) did not alter basal release of amylase. At higher concentrations of thymol (10-3 M), chlorpromazine (10-3 M) and propranolol (104M), dissociated acinar cells were lysed as indicated by an increase in release of lactic dehydrogenase (LDH).4. Ionophore A23187, CCK-PZ (maximal effective concentrations, 0*01 u. ml.-'), bethanechol (maximal effective concentrations, 10-4 M) and glucagon increased amylase secretion in a dose-dependent fashion. Concentrations of CCK-PZ and bethanechol beyond optimal levels decreased amylase secretion. Concentrations of ionophore A23187 and glucagon when tested beyond 10-6 M and 104 M respectively increased the release of LDH. In concentrations that were non-toxic, membrane stabilizers blocked the stimulating effect of chlolecystokinin-pancreozymin and bethanechol on amylase secretion but did not alter the response to A23187 and glucagon.5. Unlike bethanechol, glucagon neither increased the uptake of 45Ca nor did it alter the release of 45Ca from cells previously loaded with 45CaCl2.6. These data provide evidence that stimulus-secretion coupling in dissociated pancreatic acinar cells is basically similar to cells in situ. The effect of glucagon is consistent with the model in which hormone-dependent mobilization of Ca2+ from intra-or extracellular sources is bypassed leading to digestive enzyme secretion.

On the calcium receptor activating exocytosis: inhibitory effects of calmodulin‐interacting drugs on rat mast cells.

“…Unlike contraction, exocytosis involves complex membrane interactions -and cell membranes are a classic site of action of neuroleptic drugs which not only block ion channels and receptors for various autacoids but additionally have ' unspecific' effects on membranes that include ' stabilization', 'destabilization' and displacement of membrane-bound Ca (Seeman, 1972;Lullman et al 1980). Indeed, such unspecific membrane effects have been commonly invoked to explain effects of these drugs on exocytosis and on membrane fusion-fission processes in general (see, for example, Poste & Allison, 1973;Williams et al 1977;Elferink, 1979;Singh, 1980). Nevertheless, our results indicate some other, more specific, action.…”

“…It 240 W. W. DOUGLAS AND E. F. NEMETH is sufficient to explain the inhibition of responses to 48/80, which was acheived with similar concentrations of each of the drugs; but an additional component seems to contribute to the inhibition of responses to antigen since the drugs were active in lower concentration and in a somewhat different rank order of potency. Because antigen, unlike 48/80, acts mainly by opening membrane Ca channels, this may be the process that is additionally affected; neuroleptic drugs inhibit stimulus-induced Ca influx in various other secretary cells (see Williams et al 1977;Singh, 1980;Fleckman, Erlichman, Schubart & Fleischer, 1981;Valverde, Sener, Lebrun, Herchuelz & Malaisse, 1981) and smooth muscles (see Chaturvedi, Landon & Rama Sastry, 1978).…”

Interaction of Islet Hormones with Cholecystokinin Octapeptide‐Evoked Secretory Responses in the Isolated Pancreas of Normal and Diabetic Rats

“…In previous studies it has been reported that the effect of Som on pancreatic amylase output could be inhibitory or stimulatory, or there might be no effect, depending on whether it was an in vivo or an in vitro study, the concentration of Som or the species of animal (Holst, 1993;Owyang, 1993;Adeghate et al 1997). In contrast, Glu evoked a monophasic secretory response similar to results obtained in previous studies (Singh, 1980;Pandol et al 1983;Adeghate et al 1997). The concentrations of Som or Glu employed in this study have previously been shown to elicit only small increases in amylase secretion (Pandol et al 1983;Owyang, 1993;Adeghate et al 1998).…”

“…This potentiatory action of Ins on ACh-evoked enzyme secretion is believed to be associated with the mobilization of cellular Ca¥ and cAMP metabolism (Singh, 1983(Singh, , 1985bJuma et al 1997a) and zymogen granular regulatory protein phosphorylation (Burnham & Williams, 1982;Williams & Goldfine, 1993). Glu on its part has been shown to increase amylase secretion from dissociated pancreatic acinar cells (Singh, 1980;Pandol et al 1983). The effect of Som on pancreatic amylase secretion has not been throughly investigated and moreover, the role of islet hormones such as Glu and Som in the control of pancreatic enzyme secretion and their interaction with the classical secretagogue CCK in normal and diabetic animals are not yet understood.…”

Thymol, a constituent of thyme essential oil, is a positive allosteric modulator of human GABAA receptors and a homo‐oligomeric GABA receptor from Drosophila melanogaster

“…Many chemicals that are volatile and lipophilic, physicochemical properties shared by thymol, have anaesthetic effects in humans; furthermore, at therapeutic concentrations, ion channels are the principal targets of anaesthetics (Yamakura et al, 2001), but for many years this was thought to be an indirect action secondary to bilayer disordering, for example, detergents and free fatty acids affect receptor channel function in this way (Koenig & Martin, 1992). Thymol is known to affect plasma membrane properties such as stability (Singh, 1980;Manabe et al, 1987) and permeability to drugs, for example, piroxicam (Doliwa et al, 2001). In our study, thymol did not affect bilayer integrity at the concentrations required for potentiation, as negligible changes in the current required to clamp the membrane potential (o10 nA) occurred in uninjected oocytes.…”