Guanine nucleotide effects on agonist binding to serotonin 5HT2 receptors in rat frontal cortex

Specific [3H]ketanserin binding to serotonin 5-HT2 receptors of rat frontal cortex tissue is of high affinity, saturable and unaffected by guanine nucleotides. Antagonists displace [3H]ketanserin from a single recognition site (pseudo-Hill coefficients close to unity), which is also unaffected by guanine nucleotides. Agonist displacement of either [3H]ketanserin or [3H]spiperone from three different membrane preparations showed pseudo-Hill coefficients less than one, and may be described in terms of two agonist binding sites with differing agonist affinities. In the presence of guanine nucleotides, overall agonist affinity was lowered slightly, with little or no change in pseudo-Hill coefficient.