Abstract. To assess whether junctional coupling is involved in the secretory activity of pancreatic acinar cells, dispersed rat acini were incubated for 30 min in the presence of either heptanol (3.5 mM) or octanol (1.0 mM). Exposure to either alkanol caused a marked uncoupling of the acinar cells which, in control acini, were extensively coupled. Uncoupling was associated with an increased basal release of amylase that was at least twice that of controls. By contrast, carbamylcholine (10 -5 M)-induced maximal amylase secretion, cytosolic pH, and free Ca 2÷, as well as the structure of gap junctions joining the acinar cells, were unaffected. Both uncoupling and the alteration of basal secretion were already observed after only 5 rain of exposure to heptanol, they both persisted throughout the 30-rain exposure to the alkanols, and were reversible after removal of either heptanol or octanol. Since neither of the two uncouplers appeared to alter unspecifically the secretory machinery and the nonjunctional membrane of acinar cells, the data are consistent with the view that junctional coupling participates in the control of the basal secretion of acinar cells.AP junctions (11) and coupling (10, 17, 31) have been described for a long time between the acinar cells of the exocrine pancreas, but their function in these cells is still undetermined, as is the case in most other electrically inexcitable adult tissues (13, 20). The observation that dispersed acinar cells do not respond to secretagogues as isolated acini (1,12,27,38) led to suggest that direct interactions between neighboring cells may play a role in the normal functioning of the pancreatic acinus. The additional finding that several secretagogues uncouple the cells of pancreatic acini at concentrations that elicit maximal enzyme secretion (9, 15,16,28) further suggested that if junctional coupling is related to the secretory activity of acinar cells (28-30), it is probably not obligatory for their acute maximal secretory response. As yet, however, the possible relationship between acinar cell-to-cell coupling and enzyme secretion has not been investigated. To approach this question, we have studied whether a short period of reversible uncoupling affects amylase secretion from dispersed rat acini.Among the methods available to induce uncoupling, those that affect cytosolic free Ca 2+ ([Ca2+]i),l cytosolic pH (pHi), or ATP (20, 34) are not appropriate for this study since these factors are also involved in the control of secretion and, thus, make it impossible to establish whether secretory changes are specifically related to uncoupling. Antibodies directed against gap junctions appear as ideal tools to address this question. Unfortunately, the antibodies so far available are active only -1. Abbreviations used in this paper: [Ca2+], cytosolic free Ca2+; control KRB, Krebs-Ringer-bicarbonate medium containing 12.5 mM Hepes and 0.1% serum albumin; pH,, cytosolic pH. upon intracellular application (14,18,36) and presently cannot be incorporated into the relative...

We report here that heptanol (3.5 mM) induces in vitro a rapid formation of smooth endoplasmic reticulum aggregates (SERA) within isolated islets of Langerhans. SERA appeared after only 15 min of exposure to the alkanol and increased in number during the first 30 min of incubation. At that time, SERA represented 2% and 6% of the volume of B- and non-B-cells, respectively. Removal of heptanol resulted in the rapid disappearance of SERA, whereas reintroduction of the alkanol rapidly induced these structures again. SERA formation was seen in different types of endocrine and nonendocrine islet cells. In the insulin-producing B-cells, SERA formation was not modified by conditions known to alter the secretory activity and the microtubular-microfilament network or to inhibit protein synthesis. By contrast, SERA formation was inhibited by low temperature and by conditions depleting the energy sources of the cells. Similar observations were made in the presence of either octanol (1 mM) or nonanol (1 mM) but not of shorter chain alkanols, alkanes, oxidative derivates of either heptanol or octanol, and of other unrelated lipid-soluble compounds. Incubations in the presence of long-chain alkanols provide, therefore, a unique model to study in vitro the formation and disposal of smooth endoplasmic reticulum, as well as a system in which rapid membrane biogenesis is amenable to direct experimental testing.