Stimulation of receptors coupled to G(q)/G(11) protein may induce phosphorylation on a tyrosine residue of the alpha subunit of this G protein, which is an essential event for G(q)/G(11) activation. Here we observed that in HEK293 cells stably expressing high levels of thyrotropin-releasing hormone (TRH) receptors and G(11)alpha protein the maximal tyrosine phosphorylation of G(q)/G(11)alpha was reached within 10 min of TRH stimulation and then it faded away at longer time periods of agonist exposure. The G(q)/G(11)alpha protein levels did not change during this treatment. Incubation of intact cells with beta-cyclodextrin (betaCD) for 40 min prior to hormone exposure significantly decreased the rapid transient tyrosine phosphorylation. Subsequent replenishment of cholesterol levels reversed the former negative effect of betaCD. Isolation of caveolin-enriched, detergent-resistant membrane domains indicated destruction of these structures in betaCD-treated cells. These data indicate that the preserved integrity of plasma membrane domains/caveolae is required for complete agonist-induced phosphorylation of G(q)/G(11)alpha. (C) 2005 Elsevier Inc. All rights reserved.