Selectively Enhanced Cellular Signaling by G i Proteins in Essential Hypertension

Abstract

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.