Polar surface distribution of type II insulin-like growth factor receptor in rat hepatocytes

We describe the distribution of type II insulin-like growth factor receptors among canalicular (cLPM) and basolateral (bLPM) subfractions of rat liver plasma membranes (LPM). BLPM bound 3 times more 125I-IGF II than cLPM. The number of receptors was (1.3 +/- 0.15) X 10(-12) mol/mg in bLPM, and (0.4 +/- 0.17) X 10(-12) mol/mg in cLPM. Insulin-like growth factor II (IGF II) was 10 times more potent than insulin-like growth factor I (IGF I) in displacing 125I-IGF II from both basolateral and canalicular binding sites. Insulin did not interfere with binding of 125I-IGF II in either LPM preparations. Our findings point to an asymmetrical hepatocellular distribution of type II IGF receptors, thus extending the concept of surface polarization of hepatocytes to growth promoting hormone receptors.