Potassium, Sodium, and Chloride Ions

Cell membranes contain selective ion channels that are highly discriminatory for potassium ions, sodium ions, calcium ions, and the proton. For instance, the highly selective potassium channels of nerves show selectivity for ions as Li Na K Rb Cs, and calcium channels show selectivity as Mg Ca Sr Ba. Ion selection operates on the basis of size and repulsion, not 

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Loop diuretics work by increasing the excretion of electrolytes (sodium, chloride, potassium) which the body normally uses to maintain intra cellular and extracellular water. Monitoring of the re-absorption of potassium, sodium, and chloride ions during use should have been a must, but few did so. Lasix can and has caused death. 

Several of the monatomic cations play important roles in our bodies. For example, we need calcium ions in our diet for making bones and teeth. Iron(ll) ions are found in hemoglobin molecules in red blood cells that carry oxygen from our lungs to the tissues of our bodies. Potassium, sodium, and chloride ions play a crucial role in the transfer of information between nerve cells. Enzymes (chemicals in the body that increase the speed of chemical reactions) ofren contain metallic cations, such as manganese(II) ions, iron(III) ions, copper(II) ions, and zinc ions. For example, Zn " " ions are in the center of the enzyme alcohol dehydrogenase, which is the enzyme in our livers that accelerates the breakdown of the ethanol consumed in alcoholic beverages. 

Methybcanthine Diuretics. The mild diuretic effect of drinking coffee, from caffeine, and tea, mainly from theophylline, has been recogni2ed for along time. But the methylxanthines (Table 5) are of very limited efficacy when used as diuretics. The excretion of sodium and chloride ions are increased, but the potassium excretion is normal. Methylxanthines do not alter the urinary pH. Even though the methylxanthines have been demonstrated to have minor direct effects in the renal tubules, it is beUeved that they exert their diuretic effects through increased renal blood flow and GER (71). 

Physically, ion channels are tiny pores that stud the surface of all cells. The ion channels are important for, among other things, the function of muscles and the nervous system. These channels allow the passage of potassium, calcium, sodium, and chloride ions. Through a balance of electrical forces and chemical bonds, ion channels are specific for one ion for instance, a potassium ion channel will reject a sodium ion trying to enter its channel. An excellent visualization of the overall process is found at the website http //www. rockefeller.edu/pubinfo/howkion.html. It will be helpful to look at this website before going any further in the discussion. 

Another important diuretic contains both triamterene and hydrochlorothiazide. Triamterene is a diuretic and is known to increase sodium and chloride ion excretion but not potassium ion. It is used in conjunction with a hydrothiazide, which is an excellent diuretic but also gives significant loss of potassium and bicarbonate ions. If the triamterene were not included potassium chloride would have to be added to the diet. Hydrochlorothiazide is an antihypertensive agent as well but, unlike other antihypertensives, it lowers blood pressure only when it is too high, and not in normotensive individuals. These two drugs are made by a number of different manufacturers and do not appear in our top 35 list, but they would rank high if all brands were combined. 

The nephronic parts of the kidney are the principal diuretic active sites for secreting ede-matic fluid from the organism. Diuretics basically increase secretion of water and salts from the kidneys by suppressing reabsorption of a few main ions (primarily sodium and chloride ions) however, secretion of calcium, potassium, magnesium, and hydrocarbonate ions also increases to some degree. 

Figure 4.13 — (A) Serially arranged ISEs for the simultaneous determination of sodium, potassium, calcium and chloride ions. (B) Serially and parallelly arranged ISEs for the simultaneous determination of T, Br", Cl and F . WE working electrode PC personal computer Ej-E r, Cr, Br" and F ISEs, respectively C C3 amalgamated-lead columns (1.5 and 2.5 cm long, respectively) AgCl column RE reference electrode PHM pH/mV-meter S sample injection CS carrier stream P pump R chart recorder W waste. (Reproduced from [126] and [127] with permission of Elsevier Science Publishers and Pergamon Press, respectively).

Adrenocorticoid hormones are produced in the adrenal glands. They regulate a variety of metaholic processes. The most important mineralo-corticoid is aldosterone, an aldehyde as well as a ketone, which regulates the reahsorption of sodium and chloride ions in the kidney, and increases the loss of potassium ions. Aldosterone is secreted when hlood sodium ion levels are too low to cause the kidney to retain sodium ions. If sodium levels are elevated, aldosterone is not secreted, so some sodium will he lost in the urine and water. Aldosterone also controls swelling in the tissues. 

Excessive retention of sodium ions in the body leads to increased release of antidiuretic hormone and a resulting increase in body water. Many diuretics such as chlorothiazide (i) and clopamide (2) inhibit sodium and chloride ion resorption in the kidney tubules and promote potassium depletion, whereas amiloride (J) and triamterene ( 4) diminish the excretion of potassium while causing a loss of sodium ions6. Other diuretics such as acetazolamide (5) and dichlorphenamide (6) inhibit the ion-exchange reaction catalysed by the zinc-containing enzyme carbonic an-hydrase. 

Dyazide , a diuretic, contains both triamterene and hydrochlorothiazide. Triamterene is a diuretic and is known to increase sodium and chloride ion excretion but not potassium ion. 

The nerve cell membrane separates the external from the internal cell fluid, as does any cell membrane. As is true of virtually all cells, the intra- and extracellular fluids are electrolytic solutions of almost equal conductivity, but their chemical composition is very different. The ions present in largest quantities are sodium and potassium. The species in the external fluid are made up of more than 90 per cent sodium and chloride ions in the cell interior there are principally potassium and organic ions that cannot pass through the membrane, only 10 per cent of the ions being sodium and chloride. 

Evidence for ion channels in biological membranes was introduced in the 1970s. Possibly the most significant experiment was by Neher and Sakmann, who recorded single ion channel currents in muscle fibers. Many types of channels for sodium, potassium, calcium, and chloride ions have been described, and... 

Martinez-Maldonado Cordova 1990, Rose 1989, 1991, Wilcox 1991). In the absence of a loop diuretic, sodium ions transported into the cell are translocated into the peritubular capillary by the action of the Na, K -ATPase pump. Chloride ions are translocated out of the cell by two pathways a selective chloride channel and an electroneutral K, Cr-cotransporter. These processes maintain low intracellular sodium and chloride ion concentrations and favor continued entry of sodium and chloride from the tubular lumen. In contrast, potassium ion concentrations in the tubular fluid and within the cell are lower and higher, respectively, compared with sodium and chloride. Although these potassium ion concentrations would seem to inhibit the action of the Na, K, 2Cr-cotrans-porter, this problem is overcome by the recycling of much of the reabsorbed potassium (that does... 

Aldosterone acts in the connecting segments and collecting ducts to increase the reabsorption of sodium and chloride ions and promote the excretion of potassium and hydrogen ions. As with all steroid hormones, aldosterone acts by diffusing into the tubular cells and attaching to specific cytosolic receptors. These complexes are... 

All cells contain sodium, potassium, calcium, and chloride ions and it is found that the concentration of these ions is different inside the cell compared to the outside. The concentration of potassium inside the cell is larger than the surrounding medium, whereas the concentration of sodium and chloride ions is smaller. Thus, a concentration gradient exists across the membrane. 

Other Systemic Effects. Workers exposed for less than 5 years to TWA concentrations of 4.8-8 ppm had significantly elevated plasma sodium and chloride ions and decreased erythrocyte potassium and calcium (Pines 1982). However, the large variance in the electrolyte measurements among workers, the concomitant exposure to other chemicals, the fluctuating exposure concentrations, and the lack of a dose response for blood electrolyte alterations limit the value of this study. 

Diffusion potentials for the primary biological ions (potassium, sodium, and chloride) represent the primary source of the resting membrane potential. The diffusion potential for a given ionic species can be calculated from the modified Nernst equation developed by Hodgkin and Huxley. The equation is ordinarily written as... 

Benjamin AM, Okamoto K, Quastel JH. 1978. Effects of ammonium ions on spontaneous action potentials an on contents of sodium, potassium, ammonium and chloride ions in brain in vitro. J Neurochem 30 131-143. 

The mechanism of action of the benzothiadiazine diuretics is primarily related to their ability to inhibit the Na /cr symporter located in the distal convoluted tubule. These diuretics are actively secreted in the proximal tubule and are carried to the loop of Henie and to the distal tubule. The major site of action of these compounds is in the distal tubule, where these drugs compete for the chloride binding site of the Na /cr symporter and inhibit the reabsorption of sodium and chloride ions. For this reason, they are referred to as saluretics. They also inhibit the reabsorption of potassium and bicarbonate ions, but to a lesser degree. 

Other mineralocorticoids have an effect on the electrolytic balance of the body, but aldosterone is the most potent. Its ability to cause increased reabsorption of sodium and chloride ion and increased potassium ion excretion is approximately 3.000-fold that of hydrocortisone. A substance that antagonizes the effects of aldosterone could conceivably be a good diuretic drug. Spironolactone is such an antagonist. 

The next generation of adhesives (1970s) saw further improvements in purification of epoxy adhesives in which the chloride, potassium, sodium, and other ions were reduced to levels below 20 ppm. Outgassing was also reduced by changes in the hardeners used to cure the epoxies and by optimizing the cure schedules. The first specification for the qualification of adhesives was issued during this period by NASA s Marshall Space Flight Center in 1978. 

Sodium, potassium, and chloride, as ions (Na, K, and Gl ), are essential to electrolyte balance in body fluids. Electrolyte balance, in turn, is essential for fluid balance, acid-base balance, and transmission of nerve impulses. Table salt is the principal source of sodium and chloride ions, and dietary deficiencies are unlikely. When there is extreme fluid loss through vomiting, diarrhea, or traumatic injury, electrolytes must be supplied to restore their concentration in body fluids. 

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