Background and Methods Aldosterone is important in the pathophysiology of heart failure. In a double-blind study, we enrolled 1663 patients who had severe heart failure and a left ventricular ejection fraction of no more than 35 percent and who were being treated with an angiotensin-converting–enzyme inhibitor, a loop diuretic, and in most cases digoxin. A total of 822 patients were randomly assigned to receive 25 mg of spironolactone daily, and 841 to receive placebo. The primary end point was death from all causes. Results The trial was discontinued early, after a mean follow-up period of 24 months, because an interim analysis determined that spironolactone was efficacious. There were 386 deaths in the placebo group (46 percent) and 284 in the spironolactone group (35 percent; relative risk of death, 0.70; 95 percent confidence interval, 0.60 to 0.82; P<0.001). This 30 percent reduction in the risk of death among patients in the spironolactone group was attributed to a lower risk of both death from prog...

https://www.nejm.org/doi/pdf/10.1056/NEJM199909023411001

The effect of spironolactone on morbidity and mortality in patients with severe heart failure. Randomized Aldactone Evaluation Study Investigators.

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phag...

/pdf/the-nox-family-of-ros-generating-nadph-oxidases-physiology-zjc88zvh59.pdf

The NOX Family of ROS-Generating NADPH Oxidases: Physiology and Pathophysiology

There has recently been rapid progress in understanding receptors that generate intracellular signals from inositol lipids. One of these lipids, phosphatidylinositol 4,5-bisphosphate, is hydrolysed to diacylglycerol and inositol trisphosphate as part of a signal transduction mechanism for controlling a variety of cellular processes including secretion, metabolism, phototransduction and cell proliferation. Diacylglycerol operates within the plane of the membrane to activate protein kinase C, whereas inositol trisphosphate is released into the cytoplasm to function as a second messenger for mobilizing intracellular calcium.

Inositol trisphosphate, a novel second messenger in cellular signal transduction.

The Na+/Ca2+ exchanger, an ion transport protein, is expressed in the plasma membrane (PM) of virtually all animal cells. It extrudes Ca2+ in parallel with the PM ATP-driven Ca2+ pump. As a reversible transporter, it also mediates Ca2+ entry in parallel with various ion channels. The energy for net Ca2+ transport by the Na+/Ca2+ exchanger and its direction depend on the Na+, Ca2+, and K+ gradients across the PM, the membrane potential, and the transport stoichiometry. In most cells, three Na+ are exchanged for one Ca2+. In vertebrate photoreceptors, some neurons, and certain other cells, K+ is transported in the same direction as Ca2+, with a coupling ratio of four Na+ to one Ca2+ plus one K+. The exchanger kinetics are affected by nontransported Ca2+, Na+, protons, ATP, and diverse other modulators. Five genes that code for the exchangers have been identified in mammals: three in the Na+/Ca2+ exchanger family (NCX1, NCX2, and NCX3) and two in the Na+/Ca2+ plus K+ family (NCKX1 and NCKX2). Genes homologous to NCX1 have been identified in frog, squid, lobster, and Drosophila. In mammals, alternatively spliced variants of NCX1 have been identified; dominant expression of these variants is cell type specific, which suggests that the variations are involved in targeting and/or functional differences. In cardiac myocytes, and probably other cell types, the exchanger serves a housekeeping role by maintaining a low intracellular Ca2+ concentration; its possible role in cardiac excitation-contraction coupling is controversial. Cellular increases in Na+ concentration lead to increases in Ca2+ concentration mediated by the Na+/Ca2+ exchanger; this is important in the therapeutic action of cardiotonic steroids like digitalis. Similarly, alterations of Na+ and Ca2+ apparently modulate basolateral K+ conductance in some epithelia, signaling in some special sense organs (e.g., photoreceptors and olfactory receptors) and Ca2+-dependent secretion in neurons and in many secretory cells. The juxtaposition of PM and sarco(endo)plasmic reticulum membranes may permit the PM Na+/Ca2+ exchanger to regulate sarco(endo)plasmic reticulum Ca2+ stores and influence cellular Ca2+ signaling.

https://www.physiology.org/doi/pdf/10.1152/physrev.1999.79.3.763

Sodium/Calcium Exchange: Its Physiological Implications

The effect of spironolactone on morbidity and mortality in patients with severe heart failure

Two-pore domain K+ (K2P) channels give rise to leak (also called background) K+ currents. The well-known role of background K+ currents is to stabilize the negative resting membrane potential and c...

/pdf/molecular-background-of-leak-k-currents-two-pore-domain-3xd1km54it.pdf

Molecular Background of Leak K+ Currents: Two-Pore Domain Potassium Channels

Formation of Functional Heterodimers between the TASK-1 and TASK-3 Two-pore Domain Potassium Channel Subunits

The present study was conducted to explore the possible contribution of a recently described leak K+ channel, TASK (TWIK-related acid-sensitive K+ channel), to the high resting K+ conductance of adrenal glomerulosa cells. Northern blot analysis showed the strongest TASK message in adrenal glomerulosa (capsular) tissue among the examined tissues including heart and brain. Single-cell PCR demonstrated TASK expression in glomerulosa cells. In patch-clamp experiments performed on isolated glomerulosa cells the inward current at −100 mV in 30 mm [K+] (reflecting mainly potassium conductance) was pH sensitive (17 ± 2% reduction when the pH changed from 7.4 to 6.7). In Xenopus oocytes injected with mRNA prepared from adrenal glomerulosa tissue the expressed K+ current at− 100 mV was virtually insensitive to tetraethylammonium (3 mm) and 4-aminopyridine (3 mm). Ba2+ (300μ m) and Cs+ (3 mm) induced voltage-dependent block. Lidocaine (1 mm) and extracellular acidification from pH 7.5 to 6.7 inhibited the current (b...

/pdf/task-twik-related-acid-sensitive-k-channel-is-expressed-in-1u9i8fb5xv.pdf

TASK (TWIK-related acid-sensitive K+ channel) is expressed in glomerulosa cells of rat adrenal cortex and inhibited by angiotensin II.

http://www.jbc.org/content/279/18/18550.full.pdf

The Two-pore Domain K+ Channel, TRESK, Is Activated by the Cytoplasmic Calcium Signal through Calcineurin

In a preceding study we showed that the highly negative resting membrane potential of rat adrenal glomerulosa cells is related to background potassium channel(s), which belong to the two-pore domain channel family. TWIK-related acid-sensitive K+ channel (TASK-1) expression was found in glomerulosa tissue, and the currents elicited by injection of glomerulosa mRNA (I(glom)) or TASK-1 cRNA (I(TASK-1)) showed remarkable similarity in Xenopus laevis oocytes. However, based on the different sensitivity of these currents to acidification, we concluded that TASK-1 may be responsible for a maximum of 25% of the weakly pH-dependent glomerulosa background K+ current. Here we demonstrate that TASK-3, a close relative of TASK-1, is expressed abundantly in glomerulosa cells. Northern blot detected TASK-3 message in adrenal glomerulosa, but not in other tissues. Quantitative RT-PCR experiments indicated even higher mRNA expression of TASK-3 than TASK-1 in glomerulosa tissue. Similarly to the glomerulosa background current, the current expressed by injection of TASK-3 cRNA (I(TASK-3)) was less acid-sensitive than I(TASK-1). Ruthenium red in the micromolar range inhibited I(glom) and I(TASK-3), but not I(TASK-1). Like I(TASK-1), I(TASK-3) was inhibited by stimulation of AT1a angiotensin II receptor coexpressed with the potassium channel. The high level of expression and its pharmacological properties suggest that TASK-3 dominates the resting potassium conductance of glomerulosa cells.

/pdf/task-3-dominates-the-background-potassium-conductance-in-rat-36ce0lboi0.pdf

Péter Enyedi

Papers

Molecular Background of Leak K+ Currents: Two-Pore Domain Potassium Channels

Formation of Functional Heterodimers between the TASK-1 and TASK-3 Two-pore Domain Potassium Channel Subunits

TASK (TWIK-related acid-sensitive K+ channel) is expressed in glomerulosa cells of rat adrenal cortex and inhibited by angiotensin II.

The Two-pore Domain K+ Channel, TRESK, Is Activated by the Cytoplasmic Calcium Signal through Calcineurin

TASK-3 Dominates the Background Potassium Conductance in Rat Adrenal Glomerulosa Cells