Suspensions of dispersed islet cells were prepared by shaking collagenaseisolated pancreatic islets of ob/ob-mice in CL?+-free buffer. The dispersed cells exhibited a glucose uptake with stereospecificity for the D isomer and concentrated Rb' about 30-fold from a medium containing 70 pM RbCl. These results compare well with previous observations on unbroken islets and indicate that the dispersion procedure does not cause serious damage to the plasma membranes of the p-cells. By double isotope labeling and centrifuging the incubated cells through oil, incubation times as short as only a few seconds can be used. The elimination of the extracellular tissue space and the short incubation times should facilitate the study of transport kinetics in the pancreatic islet cells.
The transport of sugars (l-3) and amino acids (4-6) has been studied in microdissected pancreatic islets containing a high proportion of p-cells. These studies yielded valuable information on some qualitative aspects of the transport systems such as substrate specificity and cationic requirements. However, the detailed kinetics of cellular transport are difficult to study in intact islets because diffusion in the extracellular space may influence the results and preclude the use of sufficiently short incubation times. A potential solution to this problem would be the use of islet cells in suspension, provided the free cells retain their major physiological characteristics. By shaking isolated islets in Ca2+-free buffer, Lernmark (7) prepared high-yield suspensions of dispersed p-cells that were morphologically well-preserved and capable of releasing insulin in response to glucose. In the present communication we describe the use of such islet cell suspensions in transport studies. The cellular uptake of 3-O-methyl-n-glucose was studied in relation to that of inulin and Lglucose, using incubation times as short as 4 sec. In addition, the ability of the dispersed cells to accumulate Rb+ was investigated as another index of the integrity of plasma membranes. Studies by Sehlin and 73