Surface receptors for pancreatic ha hepatocytes: Qualitative and quanti hormone-target cell interactions (insulin/glucagon/pancreatic polypeptide/hepatocyte isolation/horn

In order to evaluate potential differences in the kinetics of peptide hormone-receptor interactions in hepatocytes of different species, we developed a simple procedure for the iso- lation of canine hepatocytes. Cells (obtained by collagenase per- fusion of an extirpated dog liver lobe) were isolated with uniform high viability and yield. In addition, isolated dog hepatocytes tol- erated incubation for at least 4 hr in defined medium with only a slight decrease in viability and with no change in the kinetics of (i25I)iodoinsulin or (125I)iodoglucagon binding to cell-surface re- ceptors. Comparisons of peptide hormone interactions with iso- lated dog and rat hepatocytes showed that (i) (l25I)iodoglucagon associated with specific membrane receptors more rapidly than did (251)iodoinsulin, for both rat and dog hepatocytes and at both 30'C and 37'C; (ii) the steady-state binding of (125I)iodogluca- gon at 30'C was greater than that of (125I)iodoinsulin in dog he- patocytes, but the reverse relationship held in rat hepatocytes; (iii) the rate of dissociation of (l25I)iodoinsulin from hepatocytes of both species was enhanced by the presence of the unlabeled hormone, whereas the rate of dissociation of receptor-bound (125I)iodoglucagon was enhanced by the presence of unlabeled glucagon only in hepatocytes derived from the dog; and (iv) (125I)iodopancreatic polypeptide bound to neither rat nor dog he- patocytes, although the ( 25I)iodotyrosylated peptide bound to rat hepatocytes with an unusually high apparent dissociation constant. While confirming essential findings of pancreatic hormone bind- ing to isolated hepatocytes, this comparison suggests that both