As a major cause of aldosterone producing adenomas, numerous gain-of-function mutations in the KCNJ5 gene (encoding the K(+) channel subunit GIRK4) have been identified. The human adrenocortical carcinoma cell line NCI-H295R is the most frequently used cellular model for in vitro studies related to regulation of aldosterone-synthesis. Because of the undefined role of KCNJ5 (GIRK4) in regulating synthesis of aldosterone, we aimed at identifying basal and G protein-activated GIRK4 currents in this paradigmatic cell line. The GIRK-specific blocker Tertiapin-Q did not affect basal current. Neither loading of the cells with GTP-γ-S via the patch-clamp pipette nor agonist stimulation of an infected A1-adenosine receptor resulted in activation of GIRK current. In cells co-infected with KCNJ5, robust activation of basal and adenosine-activated inward-rectifying current was observed. Although GIRK4 protein can be detected in Western blots of H295R homogenates, we suggest that GIRK4 in aldosterone-producing cells does not form functional G(βγ)-activated channels.
Genetic abnormalities have been associated with primary aldosteronism, a major cause of secondary hypertension. This includes mutations in the gene, which encodes G protein-gated inwardly rectifying K channel 4 (GIRK4). For example, the substitution of glycine with glutamic acid gives rise to the pathogenic GIRK4 mutation, which alters channel selectivity, making it more permeable to Na and Ca.
Abnormalities in G-protein-gated inwardly rectifying potassium (GIRK) channels have been implicated in diseased states of the cardiovascular system; however, the role of GIRK4 (Kir3.4) in cardiac physiology and pathophysiology has yet to be completely understood. Within the heart, the K channel, consisting of two GIRK1 and two GIRK4 subunits, plays a major role in modulating the parasympathetic nervous system's influence on cardiac physiology.
Department of Pharmaceutical Sciences, School of Pharmacy, Bouvé College of Health Sciences, Northeastern University, Boston, Massachusetts, USA; Center for Drug Discovery, Northeastern University, Boston, Massachusetts, USA; Chemistry and Chemical Biology, College of Science, Northeastern University, Boston, Massachusetts, USA. Electronic address:
G protein-sensitive inwardly rectifying potassium (GIRK) channels are important pharmaceutical targets for neuronal, cardiac, and endocrine diseases. Although a number of GIRK channel modulators have been discovered in recent years, most lack selectivity. GIRK channels function as either homomeric (i.
G protein-gated, inwardly rectifying potassium channels (GIRK) mediate inhibitory transmission in brain and heart, and are present in the adrenal cortex. GIRK4 (KCNJ5) subunits are abundant in the heart and adrenal cortex. Multiple mutations of KCNJ5 cause primary aldosteronism (PA).
Section on Endocrinology & Genetics (SEGEN), Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD), National Institutes of Health (NIH), Bethesda, MD 20892,USA.
Context: Pathogenic variants in KCNJ5, encoding the GIRK4 (Kir3.4) potassium channel, have been implicated in the pathogenesis of familial hyperaldosteronism type-III (FH-III) and sporadic primary aldosteronism (PA). In addition to aldosterone, glucocorticoids are often found elevated in PA in association with KCNJ5 pathogenic variants, albeit at subclinical levels.
