Binding of an opiate, levorphanol, to intact neuroblastoma cells in continuous culture

Mouse neuroblastoma cells in continuous culture, incubated for 1 to 2 days in the presence of 10--6 M levorphanol or morphine, were found to become tolerant to and dependent on those biologically active opiates. Examination of the interaction between levorphanol and the whole neuroblastoma cell suggested that levorphanol was binding to stereospecific opiate receptor sites. This binding was time and temperature dependent, and saturable at concentrations greater than 10--5 M levorphanol. Competition by other opiates for levorphanol sites correlated with their biological activity. This is the first evidence for saturable, stereospecific opiate binding in a homogeneous population of unhybridized cells in continuous culture.