K+ release from rat parotid cells: an alpha 1-adrenergic mediated event

To characterize alpha-adrenergic receptors in rat parotid gland tissue, 9,10-[9,10-3H(N)]-dihydro-alpha-ergocryptine ([3H]DHE) and [3H]prazosin binding to membranes and stimulated K+ release from parotid cell aggregates were examined. Prazosin (selective alpha 1-adrenergic antagonist), displacement of [3H]DHE binding from parotid membranes was biphasic, indicating the presence of both alpha 1- and alpha 2-adrenergic receptors. The numbers of alpha 1- and alpha 2-receptors were about equal. alpha 1-Adrenergic receptors were further studied by [3H]prazosin binding. [3H]Prazosin binding was a rapid, reversible, saturable and stereospecific process, with high affinity (KD = 0.38 nM) and low capacity (Bmax = 380 fmoles ligand bound/g tissue, 10.1 fmoles/mg protein) as determined by Scatchard analysis. The characteristics of [3H]prazosin binding were in good agreement with those of catecholamine-stimulated K+ release, suggesting that K+ release from rat parotid gland cells is an alpha 1-adrenergic mediated effect.