The availability of highly purified human islets has increased with th
e progressive improvement of isolation methods. This has provided oppo
rtunities to perform various in vitro studies on human islets. However
, when islets are maintained in culture, the overgrowth of fibroblasts
results in a reduced islet purity and often has an adverse effect on
islet function. To reduce fibroblast growth and to maintain normal isl
et function, we have investigated a new three-dimensional culture tech
nique using a noncoated transparent Biopore membrane insert (Millicell
CM, Millipore). Islets were isolated from seven human pancreata and c
ultured for 2 months using this membrane insert. At various time inter
vals, the functional viability of islets was assessed by measurements
of insulin released into the culture medium, static incubation assays
of basal and stimulated insulin release, islet insulin contents, and i
nsulin biosynthesis. Results were compared to those of islets cultured
in hydrophobic plastic petri dishes, our standard procedure. We found
that the non-coated membrane does not allow islet attachment to the s
urface and prevents fibroblast growth, so that islets maintain a three
-dimensional structure and remain in a free-floating form. Islets cult
ured in a membrane insert showed a function similar to or better than
that of islets cultured in plastic petri dishes.