Selectively Enhanced Cellular Signaling by Gi Proteins in Essential Hypertension

Recent studies have shown an enhanced signaling capacity of receptors coupled to pertussis toxin (PTX)–sensitive guanine nucleotide–binding proteins (G proteins) in immortalized B lymphoblasts from patients with essential hypertension. In the present study, we analyzed (1) whether such alterations would also be expressed in nontransformed cells of these individuals and (2) whether other G protein–mediated signaling pathways were also altered. Therefore, we established primary cultures of skin fibroblasts from previously characterized normotensive and hypertensive individuals (NT and HT cells, respectively). [Ca 2+ ] i rises induced by lyso -phosphatidic acid (LPA), thrombin, and sphingosine-1-phosphate as well as the formation of inositol 1,4,5-trisphosphate and [ 3 H]thymidine incorporation evoked by LPA were PTX sensitive and enhanced twofold in HT fibroblasts. In contrast, cellular responses induced by bradykinin, endothelin-1, and angiotensin II (all PTX insensitive) were similar in NT and HT cells. Formation of cAMP induced by stimulation of G s with isoproterenol was identical in NT and HT cells. Western blot analysis yielded no evidence for an overexpression of Gα i2 , Gα i3 , Gβ 2 , and Gβ 4 . Furthermore, sequencing of cDNAs encoding for the ubiquitously expressed PTX-sensitive G protein subunits Gα i2 , Gα i3 , Gβ 1 , and Gβ 2 from NT and HT cell lines yielded no evidence for mutations in these genes. Although the molecular mechanisms remain to be defined, these data support the concept of a selective enhancement of signal transduction via PTX-sensitive G proteins in essential hypertension.