Characterization of the alpha 1B-adrenergic receptors of chicken hepatocytes. Signal transduction and actions

1. In chicken hepatocytes, alpha 1-adrenoceptor activation increased: (a) phosphatidylinositol labeling; (b) production of inositol trisphosphate; (c) cytosol calcium; and (d) phosphorylase activity. 2. Prazosin (Ki approximately 0.2-0.4 nM) was more potent in inhibiting these actions than 5-methyl-urapidil (Ki approximately 30-60 nM); these actions were sensitive to chlorethylclonidine suggesting the involvement of alpha 1B-adrenoceptors. 3. The stimulation of phosphoinositide turnover was insensitive to pertussis toxin. 4. In chicken liver membranes, [3H]prazosin binding sites (Bmax 872 fmol/mg protein) with high affinity for prazosin (KD 0.3 nM; Ki 0.4 nM) and lower affinity for 5-methyl-urapidil (Ki 46 nM) were detected, consistent with the presence of alpha 1B-adrenoceptors.