Specific binding and metabolism of (-)- and (+)-[3H]-nicotine in isolated rat hepatocytes and hepatocyte membranes.

The specific binding of (-)- and (+)-[3H]-nicotine, as well as their relative rates of metabolism, were investigated in isolated rat hepatocytes and hepatocyte membranes. A Scatchard plot of both [3H]-enantiomers revealed two components, with the higher affinity site having Kd values of 2 X 10(-10) and 3 X 10(-9) M and Bmax values of 5 X 10(-15) and 4 X 10(-15) moles/mg protein for the (-)- and (+)-enantiomers, respectively. The lower affinity site for both enantiomers had a Kd of 4 X 10(-9) M and Bmax of 5 X 10(-14) moles/mg protein. The pH optimum of binding was in the higher pH range, in contrast to brain membranes where the optimum was 6.5 involving the protonated form of nicotine. A good correlation was observed between the pharmacologic potency of a group of nicotine analogues and their ability to bind to intact and hepatocyte membranes. The rate of conversion of nicotine to cotinine in hepatocytes membranes. The rate of conversion of nicotine to cotinine in hepatocytes is related to the degree of binding and accumulation. The results are discussed in terms of the possible relationship of the nicotine binding and translocation to its metabolism.