A: Separation of plasma membrane and mitochondrial fractions in Percoll gradient; flotation of plasma membrane fraction in sucrose gradient.
B: Determination of G protein activity - [³⁵S]GTPγS binding in Percoll-purified plasma membranes (rat brain cortex):
Comparison of the dose-response curves of agonist stimulation at a single [³⁵S]GTPγS concentration indicated the order of efficacy: baclofen (GABA_B-receptor) > DADLE (d-opioid receptor) > DAMGO (m-opioid receptor) > U-69593 (k-opioid receptor).