Role of a Guanine Nucleotide-Binding Protein in α 1 -Adrenergic Receptor-Mediated Ca 2+ Mobilization in DDT 1 MF-2 Cells

Abstract

Abstract

In this study the mechanisms involved in α₁adrenergic receptor-mediated Ca²⁺ mobilization at the level of the plasma membrane were investigated. Stimulation of ⁴⁵Ca²⁺ efflux from saponin-permeabilized DDT₁ MF-2 cells was observed with the addition of either the α₁ adrenergic agonist phenylephrine and guanosine-5′-triphosphate or the nonhydrolyzable guanine nucleotide guanylyl-imidodiphosphate. In the presence of [³²P]NAD, pertussis toxin was found to catalyze ADP-ribosylation of a M _r = 40,500 (n = 8) peptide in membranes prepared from DDT₁ MF-2 cells, possibly the α-subunit of N_i However, stimulation of unidirectional ⁴⁵Ca²⁺ efflux by phenylephrine was not affected by previous treatment of cells with 100 ng/ml pertussis toxin. These data suggest that the putative guanine nucleotide-binding protein which couples the α₁-adrenergic receptor to Ca²⁺ mobilization in DDT₁ MF-2 cells is not a pertussis toxin substrate and may possibly be an additional member of the guanine nucleotide binding protein family.