Similar effects of saponin treatment and aging on coupling of alpha 1-adrenergic receptor-G-protein.

The effects of the nonionic detergent saponin on alpha 1-adrenergic signal transduction were investigated using rat parotid cells and membrane preparations. Fifty microM epinephrine-stimulated 45Ca2+ efflux and inositol 1,4,5-triphosphate (Ins[1,4,5]P3) production in adult parotid cells were significantly decreased after saponin treatment. Saponin did not alter the concentration of alpha 1-adrenergic receptors labeled by [3H]prazosin, but significantly reduced the guanosine imido diphosphate (GppNHp)-induced shift from high to low affinity sites. Fifty microM epinephrine-stimulated high affinity GTPase activity was also reduced by saponin treatment. These data suggest that reduced alpha 1-adrenergic receptor-stimulated functional responsiveness following saponin treatment may be due to impaired uncoupling of receptor-G-protein complexes.