Influence of divalent cations on the detection of somatogenic and lactogenic binding sites in mouse liver cells.

Specific binding of 125I-labelled human somatotropin was demonstrated in isolated hepatocytes from male mice. In the presence of divalent cations (Ca2+ and Mg2+) the binding of 125I-labelled human somatotropin was competitive with ovine prolactin. Scatchard analysis of competition data indicated a KD of 1.4 +/- 0.2 nM and a binding capacity of 13 000 +/- 2000 sites/cell. In the absence of divalent cations and in the presence of EDTA, human and bovine somatotropins were found to be equally effective to displace bound 125I-labelled human somatotropin, while ovine prolactin showed a weak competition. In this case, the binding capacity was 8400 +/- 1500 sites/cell and the KD was 1.1 +/- 0.1 nM.