The G-proteins which regulate hormonal turnover of phosphoinositide (PI) in human umbilical vein endothelial cells have been investigated. A 40-41 kDa doublet present in the membranes of these cells was selectively ADP ribosylated by pertussis toxin (PTx), and this doublet was G,, and G,, according to immunoblotting with specific antisera. By contrast, a doublet of 24-26 kDa proteins in the same membrane preparations was ADP ribosylated by the C, component of botulinum toxin (BoTx). PTx-dependent ADP ribosylation blocked stimulation of PI turnover by histamine, but did not affect stimulation by bradykinin, whereas BoTx (C, + C, components) had the opposite effect. Thus two different groups of G-proteins may be involved in hormone-dependent stimulation of PI turnover in human umbilical vein endothelial cells.Protein, G-; Phosphoinositide turnover; (Human umbilical vein endothelial cell)
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