Altered calcium concentration and rabbit atrial H1-receptors

Ascorbate increases apparent "specific" binding of [3H]pyrilamine to glass fiber filters

Although filtration through glass fiber filters provides a convenient method for separating bound from unbound radioligand, binding of the ligand to the filters is often a problem. Ascorbate (0.1%) has been shown to decrease binding of serotonergic acids to these filters. In the present study, relatively high binding of [3H]pyrilamine, an H1-antagonist, to glass fiber filters was observed. The addition of ascorbate increased, rather than decreased, binding of [3H]pyrilamine to the filters. Thus, the effect of ascorbate on binding of radioligands to glass fiber filters appears to be dependent upon the particular ligand involved.

Correlation of histamine H1 receptor function and [3H]mepyramine binding in porcine tracheal tissue

In order to validate the use of [3H]mepyramine as a radioligand to label airway histamine H1 receptors, the results of radioligand binding experiments using porcine tracheal tissue membranes were compared with the results of physiologic studies measuring histamine-induced trachealis muscle contraction. Close agreement was found between histamine-induced [3H]mepyramine binding inhibition and histamine concentration-contraction-response curves. Close agreement was also found between the KD of mepyramine-induced [3H]mepyramine binding inhibition and the K beta of mepyramine antagonism of muscle contractions stimulated by 10(-4) M histamine. [3H]Mepyramine binding was found to be rapid, reversible, saturable and stereospecific. Only H1 agonists and antagonists displayed potent [3H]mepyramine binding inhibition in competition binding studies. The results fulfill criteria for histamine H1 receptor identification by radioligand binding with [3H]mepyramine.