Insulin secretion from perifused rat pancreatic pseudoislets

Abstract

Isolated adult rat pancreatic islets were dispersed into single cells and cultured free-floating for 3 to 4 d, during which time islet cells reaggregated spontaneously into spherical clusters or pseudoislets. The gross morphology of these tissues resembled nondissociated islets. Electron microscopy revealed well-preserved cell ultrastructure and intercellular membrane connections. Immunofluorescent localization of islet cell types showed that A cells tended to be peripherally distributed around a B cell core, with D cells scattered throughout the aggregate mass. The dynamics of insulin release from pseudoislets were evaluated in vitro by perifusion techniques. Pseudoislets exhibited clear biphasic dose-dependent insulin responses to 30 min glucose stimulation over the range 5.5 to 30 mM. Repeated 2-min pulses with 22 mM glucose elicited brief monophasic spikes of insulin release of consistent magnitude. L-Arginine (5 to 20 mM) evoked biphasic insulin release but these responses were not dose-dependent. These data indicate that islet cells reaggregate into structures with close morphologic similarities to intact islets, and that pseudoislet B cells continue to secrete insulin in response to nutrient secretagogues, comparable to that seen with islets in vitro and in situ.

Role of islet structure and cellular interactions in the control of insulin secretion

“…39 Thus despite immortalization, the mouse cell lines used appear to retain sufficient molecular expression and distinct islet phentoypes which allow them to aggregate in a manner consistent with that observed in primary rodent islets. This is consistent with the early observations of Halban 54 and Hopcroft 14 and colleagues. Interestingly, the acute insulin secretory response to glucose was less from heterotypic pseudoislets than from MIN6 pseudoislets.…”

Delta cell secretory responses to insulin secretagogues are not mediated indirectly by insulin

“…Previous work has demonstrated that interactions between cells within the islet are essential for ensuring the appropriate pattern of insulin secretion [1][2][3][4][5]; and possible interactions between alpha and beta cells within islets have been well studied [1,[6][7][8][9]. For example, alpha cells express the insulin receptor [7] and a number of studies suggest that beta cells negatively regulate glucagon secretion, although it is uncertain whether the paracrine agent is insulin, zinc co-released with insulin or some other beta cell secretory product [7][8][9][10].…”

Tumor necrosis factor-alpha modifies adhesion properties of rat islet B cells.

“…When rat islet cells are dissociated with trypsin and allowed to reaggregate in culture, they form islet-like structures, with B cells in the center surrounded by a rim of non-B cells (8)(9)(10).…”

“…Such "pseudoislets" have been proposed as a model to study the influence of islet cell interrelationships upon islet function (9)(10)(11)(12). The ability of islet cells to form islet-like organoids suggests a cell type-specific expression of cell adhesion molecules (CAMs)' responsible for selective recognition/adhesion and segregation between B and non-B cells.…”