Abstract
Using [3H]QNB, we demonstrated that GTP and Gpp(NH)p increased muscarinic receptor high affinity sites in bovine tracheal muscle preparations; however, neither the dissociation constant of [3H]QNB binding sites nor pulmonary β-adrenergic receptor sites was altered. The GTP effect on increasing the receptor sites was relatively small (16%), sensitive (ED50 0.48 μM) and specific (Gpp(NH)p > GTP = GDP > GMP ≫ ATP). Mg2+ potentiated this increase by up to 94.8%, whereas Na+, K+ and Ca2+ had no such effect.