Regulation and critical role of potassium homeostasis in apoptosis.

Energy deficiency and dysfunction of the Na+, K+-ATPase are common consequences of many pathological insults. The nature and mechanism of cell injury induced by impaired Na+, K+-ATPase, however, are not well defined. We used cultured cortical neurons to examine the hypothesis that blocking the Na+, K+-ATPase induces apoptosis by depleting cellular K+ and, concurrently, induces necrotic injury in the same cells by increasing intracellular Ca2+ and Na+. The Na+, K+-ATPase inhibitor ouabain induced concentration-dependent neuronal death. Ouabain triggered transient neuronal cell swelling followed by cell shrinkage, accompanied by intracellular Ca2+ and Na+ increase, K+ decrease, cytochrome c release, caspase-3 activation, and DNA laddering. Electron microscopy revealed the coexistence of ultrastructural features of both apoptosis and necrosis in individual cells. The caspase inhibitor Z-Val-Ala-Asp(OMe)-fluoromethyl ketone (Z-VAD-FMK) blocked >50% of ouabain-induced neuronal death. Potassium channel blockers or high K+ medium, but not Ca2+ channel blockade, prevented cytochrome c release, caspase activation, and DNA damage. Blocking of K+, Ca2+, or Na+ channels or high K+ medium each attenuated the ouabain-induced cell death; combined inhibition of K+ channels and Ca2+ or Na+ channels resulted in additional protection. Moreover, coapplication of Z-VAD-FMK and nifedipine produced virtually complete neuroprotection. These results suggest that the neuronal death associated with Na+, K+-pump failure consists of concurrent apoptotic and necrotic components, mediated by intracellular depletion of K+ and accumulation of Ca2+ and Na+, respectively. The ouabain-induced hybrid death may represent a distinct form of cell death related to the brain injury of inadequate energy supply and disrupted ion homeostasis.

https://www.jneurosci.org/content/jneuro/22/4/1350.full.pdf

Ionic Mechanism of Ouabain-Induced Concurrent Apoptosis and Necrosis in Individual Cultured Cortical Neurons

The Na+, K+-ATPase (Na+, K+-pump) plays critical roles in maintaining ion homeostasis. Blocking the Na+, K+-pump may lead to apoptosis. By contrast, whether an apoptotic insult may affect the Na+, K+-pump activity is largely undefined. In cultured cortical neurons, the Na+, K+-pump activity measured as a membrane current Ipump was time-dependently suppressed by apoptotic insults including serum deprivation, staurosporine, and C2-ceramide, concomitant with depletion of intracellular ATP and production of reactive oxygen species. Signifying a putative relationship among these events, Ipump was highly sensitive to changes in ATP and reactive oxygen species levels. Moreover, the apoptosis-associated Na+, K+-pump failure and serum deprivation-induced neuronal death were antagonized by pyruvate and succinate in ATP- and reactive-oxygen-species-dependent manners. We suggest that failure of the Na+, K+-pump as a result of a combination of energy deficiency and production of reactive oxygen species is a common event in the apoptotic cascade; preserving the pump activity provides a neuroprotective strategy in certain pathological conditions.

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Apoptotic insults impair Na+, K+-ATPase activity as a mechanism of neuronal death mediated by concurrent ATP deficiency and oxidant stress.

Aggregating platelets release serotonin, which induces contraction of most vascular smooth muscle by activation of S2-serotoninergic receptors. Serotonin released in the circulation may contribute to the increase in peripheral resistance of hypertension as the responsiveness of blood vessels from hypertensive animals and humans to the vasoconstrictor action of the monoamine is augmented. The data obtained with the new antihypertensive agent ketanserin may favor that interpretation. Ketanserin is a selective S2-serotoninergic antagonist with additional alpha 1-adrenergic blocking properties. In humans, it has a terminal half-life of 12 to 25 hours and is eliminated predominantly by the liver. The hemodynamic profile of ketanserin is that of a vasodilator drug with actions on both resistance and capacitance vessels. On short-term intravenous administration, it lowers blood pressure in hypertensive patients with minimal reflex changes in cardiovascular function. When given orally long term to hypertensive patients, ketanserin causes a sustained reduction in arterial blood pressure, comparable to that obtained with either beta-adrenergic blockers or diuretics. Several studies have shown a greater efficacy in older (greater than 60 years of age) than in younger patients independent of starting pressure. Side effects mainly consist of dizziness, somnolence, and dry mouth, but they are usually not severe. The mechanism underlying the antihypertensive effect of ketanserin is unclear. It cannot be attributed to either S2-serotoninergic or alpha 1-adrenergic blockade alone, but an interaction between the two effects appears to be required.

Serotoninergic mechanisms in hypertension. Focus on the effects of ketanserin.

Gender-related differences in sodium (Na+) metabolism, Na+ transport through cell membrane, intracellular Na+ concentration, and Na+ urinary excretion review is presented in the article. Literature data on gender-related differences in the occurrence of hyponatremia and related neurology are overviewed. Some of the drugs used in neurology (carbamazepine, oxcarbazepine, thiazides, antidepressants) are pointed out as eventual sources of hyponatremia. This disorder shows a clear-cut preference of the feminine gender. The authors present literature data on gender-related differences in the mechanisms of Na+ transport (Na+/H+ exchange, Na+/K+/2Cl- cotransport, Na+, K+-ATPase). The reasons for such differences are not yet known. Investigative tests with animals of both genders, cellular studies and clinical investigations with human males and females could help to answer question why females are more prone to hyponatremia, to select more efficient measures for prevention of hyponatremia and to differentiate specific peculiarities of treatment for patients of either sex.

/pdf/gender-differences-of-sodium-metabolism-and-hyponatremia-as-2cg1igiifv.pdf

Gender differences of sodium metabolism and hyponatremia as an adverse drug effect.

The red cell Na+,K+-ATPase pump activity estimated by the ouabain-sensitive 86Rb-uptake or Na+-efflux, the Na+,K+-cotransport activity measured either by the furosemide-sensitive K+- or Na+- efflux or by the ethacrynic acid-sensitive 86Rb-uptake as well as the intraerythrocyte concentration of sodium, potassium and magnesium were studied in 29 normal male subjects with one to three weeks interval between the first and second blood sampling. Both the red cell sodium and potassium concentration, the erythrocyte ouabain-sensitive 86Rb-uptake and Na+-efflux, the furosemide-sensitive Na+- and K+-efflux and the ethacrynic acid-sensitive 86Rb-uptake are stable over time in the same individual. The furosemide-sensitive Na+-and K+-efflux is significantly related to the ethacrynic acid-sensitive 86Rb-uptake. The intraerythrocyte Na+ concentration was negatively related to the ouabain-sensitive 86Rb-uptake, but not to the ouabain-sensitive Na+-efflux; it was, however, negatively related to the rate constant for the ouabain-sensitive Na+-efflux.

Intracellular sodium, potassium and magnesium concentration, ouabain-sensitive 86rubidium-uptake and sodium-efflux and Na+, K+-cotransport activity in erythrocytes of normal male subjects studied on two occasions.

The reliability of the assay of intracellular Na+ and K+ concentration; Na+,K+-ATPase activity; Na+-K+ cotransport and Na+-Li+ countertransport in erythrocytes was investigated. These assays were also applied in normal male subjects with and without family history of hypertension. The various assays are reproducible as indicated by the intra-assay variation and are stable over time as shown by the inter-assay variation. A delay between blood sampling and analysis, however, result in an increase in intracellular Na+ concentration and decreases in Na+,K+-ATPase activity; Na+-K+ cotransport and Na+-Li+ countertransport. Compared to the white normal males without family history of hypertension (n = 43) red blood cells of white normal males with such a history (n = 17) have a higher (p less than 0.01) intracellular Na+ concentration. This can be at least partly due to their lower (p less than 0.001) furosemide-sensitive Na+ efflux rate. Also, their ouabain-resistant 86Rb-uptake was lower (p less than 0.05). The potassium concentration in the red blood cells was similar in both groups.

Methodological assessment of assays for intracellular concentration and transmembrane fluxes of sodium and potassium in erythrocytes of man.

Sodium concentrations in erythrocytes are lower in women during the luteal phase of the menstrual cycle than in women studied during the follicular phase and in men. Sodium cotransport activity is lower in women during the follicular phase than in men. Women taking oral contraceptives show no monthly variations in erythrocyte sodium concentrations. Subjects with a family history of essential hypertension have higher sodium concentrations in erythrocytes than those with a different family background, partly because of reduction in sodium cotransport activity. Negroes have marked erythrocyte sodium accumulation due to lower activity of the sodium-potassium pump and cotransport system; they also have reduced sodium-lithium counter-transport. There is no difference between negroes with or without haemoglobin S. There are no changes in erythrocyte potassium concentrations in relation to sex, menstrual phase, race, familial essential hypertension, presence of haemoglobin S or use of oral contraceptives. These physiological variations indicate the factors which must be standardized to study sodium concentrations in cells and sodium transmembrane flux.

Physiologic variability of erythrocyte concentrations and transport of sodium and potassium

The red cell Na+,K+-ATPase pump activity was measured either by the ouabain-sensitive 86Rb-uptake in the presence or absence of 4 mM potassium in the external medium or by the ouabain-sensitive Na+-efflux in normal male subjects without any medication (n = 14) and during short-term treatment with the serotonin-antagonist, ketanserin. The ouabain-sensitive 86Rb-uptake in a medium containing 4 mM K+ was related to the 86Rb-uptake in a K+-free medium (r = 0.82; p less than 0.001) and to the Na+ efflux (r = 0.74; p less than 0.01). The intra-erythrocyte sodium concentration was negatively related to the ouabain-sensitive 86Rb-uptake (K+-free medium r = 0.59, p less than 0.05: 4 mM K+ in medium r = -0.85; p less than 0.01) and to the ouabain-sensitive Na+ efflux (r = -0.53; p less than 0.05). During serotonin antagonism with ketanserin no changes were found in the ouabain-sensitive 86Rb-uptake or Na+-efflux.

M Laermans

Papers

Intracellular sodium, potassium and magnesium concentration, ouabain-sensitive 86rubidium-uptake and sodium-efflux and Na+, K+-cotransport activity in erythrocytes of normal male subjects studied on two occasions.

Methodological assessment of assays for intracellular concentration and transmembrane fluxes of sodium and potassium in erythrocytes of man.

Physiologic variability of erythrocyte concentrations and transport of sodium and potassium

Assessment of sodium-potassium ATPase activity in human erythrocytes in vitro.

Variabilité physiologique des concentrations et des transports érythrocytaires du sodium et du potassium.