We have serially followed the function of intrahepatic canine islet autografts in 15 beagle dogs for up to 24 mo. Of these, only 20% sustained normal levels of fasting blood glucose for >15 mo posttransplant. Failure of autograft function was accompanied by a preferential loss of well-granulated beta cells in the engrafted islets. The chronic stimulation of an initially marginal intrahepatic beta-cell mass ultimately resulted in metabolic deterioration and loss of beta cells below the minimal threshold required to maintain normal fasting blood glucose levels. It is possible that transplantation of a larger mass of islets would result in indefinite graft function in dogs. However, it remains to be demonstrated in larger mammals, including humans, whether an islet cell mass that is initially adequate in a heterotopic site such as the liver can remain functionally competent over a prolonged period.

Desmosomes of larval and post-metamorphic newt epidermis have been studied by freeze-fracture replication both with and without prior glutaraldehyde fixation. Characteristic particles of a diameter (70-130 A) similar to that of typical membrane associated particles are found clustered on the exposed internal faces of adherent desmosomal membranes. They remain attached to the B-face in unfixed material, but occupy the desmosomal A-face after fixation. Membrane associated particles of nondesmosomal surfaces are found predominantly on the A-face in both fixed and unfixed epidermis. Suitably oriented replicas of unfixed desmosomes reveal profiles of apparent fine filaments extending from the region of tonofilament loops through the desmosomal plaque to traverse the cytoplasmic leaflet of the plasmalemma. They can be traced onto the B-face. Their position correlates to fine linear profiles noted in tannic acid/glutaraldehyde-fixed and sectioned desmosomes. The possibility that these represent a mechanism for anchorage of tonofilaments to the plaque and to the membrane is discussed. These and other fine structural features are compared and contrasted to the properties of hemidesmosomes described in the preceding report.

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Flow cytometry has been examined as a method to separate islet cells into homogeneous subpopulations. Collagenase-isolated rat islets were dissociated into single cells and these were analyzed and sorted according to their low forward angle light scattering properties by using automated flow cytometry. Light scatter histograms showed two peaks of viable cells. Radioimmunoassay of hormone content in cell fractions collected across the the two peaks showed that glucagon-containing cells were concentrated towards the left side of the left peak and somatostatin-containing cells were concentrated towards the right side of the left peak, whereas insulin-containing cells were clearly enriched in the right peak. The B-cell-enriched fraction (90% B cells, 3% A cells, 2% D cells) exhibited significant insulin secretory responses to glucose (16.7 mM), and 3-isobutyl-1-methylxanthine (0.1 mM), during a 24-h culture period, and these responses were slightly greater than those observed in the original mixed islet cell preparation (66% B cells, 14% A cells, and 4% D cells). These results indicate that flow cytometry can be applied to sort pancreatic islet cells into populations enriched in specific endocrine cell types for further study of the functions of individual cell types.