Cloreto e status hidroeletrolítico e ácido-básico: importância clínica da determinação laboratorial / Chloride and hydroelectrolytic and acid base status: clinical importance of laboratorial determination

Apesar de o cloreto ser um exame amplamente disponível e solicitado em instituições de saúde, a maior pane dos médicos crê ser difícil interpretar seus resultados, estabelecer correlações com outros parâmetros laboratoriais associados e tomar decisões terapêuticas baseadas no mesmo. Devido à complexidade de sua homeostase e à intrincada correlação com o status hidroeletrolítico e ácido-básico, poucos médicos se sentem efetivamente aptos a aproveitar a valiosa informação clínica que ele pode revelar. Isto é agravado pela rarefeita bibliografia objetiva sobre o tema. Os autores desta revisão não foram capazes de encontrar nenhum capítulo especificamente dedicado ao cloreto nos principais livros-texto de Fisiologia, Clínica Médica e Nefrologia, disponíveis, à exceção de três revisões bibliográficas no Medline. Não obstante, tentamos organizar a informação tão claramente quanto possível, com o objetivo de tornar o cloreto uma ferramenta útil aos nossos colegas profissionais de saúde.

Even though chloride is a widely available and requested test in health institutions, most part of physicians find it difficult to interpret its results, establish correlations with other laboratory linked parameters and take therapeutic decisions based on it. Due to the complexity of its homeostatic balance and intrincated correlation to hydroelectrolytic and acid base status, few doctors feel actually able to fully profit from the valuable clinical information it can unfold. This is aggravated by the scarce objective bibliography on the issue. The authors of this review were not able to find any chapters specifically dedicated to chloride on major Physiology, Internal Medicine and Nephrology textbooks, but only three reviews on Medline. Nevertheless, we managed to organize the information as clearly as possible with the aim of making chloride test an useful tool to our fellow health professionals.

Stimulation of Cl- secretion by AlF4- and vanadate in T84 cells

We investigated the mechanism of Cl- secretion by fluoroaluminate(AlF4-) and sodium orthovanadate(vanadate) using the human colonic T84 cell line. T84 cell monolayers grown on collagen-coated filters were mounted in Ussing chambers to measure short circuit current(ISC). Serosal addition of AlF4- or vanadate to T84 monolayers produced a sustained increase in ISC. Removal of Ca2+ from the serosal bathing solution partially inhibited AlF4-(-)and vanadate-induced ISC, and readministration of Ca2+ restored AlF4-(-)and vanadate-induced ISC. Carbachol application in the presence of forskolin, AlF4- or vanadate induced a synergistic increase of ISC. Forskolin and vanadate significantly increased cellular cAMP level, while carbachol and AlF4- did not. Carbachol, AlF4- and vanadate significantly increased [Ca2+]i. After Na+ in mucosal bathing solution was replaced with K+, and the mucosal membrane of T84 cell was permeabilized with amphotericin B, AlF4-, vanadate, and carbachol increased K+ conductance, but forskolin did not. After sodium chloride in serosal bathing solution was replaced with sodium gluconate and the serosal membrane was permeabilized with nystatin, forskolin, AlF4-, and vanadate increased Cl- conductance, but carbachol did not. AlF4-(-)induced ISC was remarkably inhibited by the pretreatment of pertussis toxin(2 micrograms/ml) for 2 hours. These results indicate that AlF4- and vanadate can increase Cl- secretion via simultaneous stimulation of Cl- channel and K+ channel in T84 cells. However, the AlF4- action is mostly attributed to stimulation of pertussis toxin-sensitive G-proteins, whereas the vanadate action mostly results from G protein-independent mechanisms.

Secretory effect of serotonin on jejunal response to cholera toxin, in dog

A substância mediadora liberada pela toxina da cólera e que estimula a secreçäo intestinal é ainda desconhecida. Sabe-se que a serotonina está envolvida no estímulo secretor intestinal de água e eletrólitos. Tendo em vista a avaliaçäo de um provável papel da serotonina na induçäo secretora jejunal pela toxina da cólera, calcularam-se os volumes de água, sódio, potássio e cloreto, bem como os níveis imunorreativos de serotonina, em alça de Thiry-Vella canina. A administraçäo de toxina provocou um aumento na secreçäo de todos os eletrólitos e do fluxo de serotonina. Esses resultados sugerem que a toxina da cólera induz à liberaçäo de serotonina na luz intestinal, talvez como um mediador da secreçäo hidroeletrolítica entérica

Active transport of the chloride ion by the colon - abstract

The present data represent some results of our continuing studies on the mechanisms of electrolyte transport in the colon. Trained dogs with chronic isolated segments of colon were used, and the transport of chloride ion was studied by instilling the following electrolyte solutions into the colon: sodium chloride (154 mEq/L, 100 mEq/L), Mannitol (5 percent) choline choride (100 mEq/L), lithium chloride (100 mEq/L), lithium chloride (60 mEq/L) plus potassium chloride (40 mEq/L), lithium chloride (75 mEq/L) plus sodium bicarbonate (75 m Eq/L). All solutions were made isotonic whenever necessary by the addition of mannitol and all contained the non-absorbable maker polyethylene glycol (PEG). Samples of colonic fluid were taken at intervals over a six-hour period following the instillation of solution into the isolated colonic segment. The samples were analysed for Na, K, Cl, HCO3 - pH, osmolality and PEG. The electrical potential difference across the colon was measured in several experiments. Chloride ion transport was also studied following the administration of Diamax or Aldosterone, mucosa. There was no evidence of active water transport. The mucosa is normally electrically negative with respect to serosa; however, in the presence of choline chloride the mucosa becomes electrically positive with respect to serosa. Our data also show that the chloride ion is actively transported against both an electrical and a chemical gradient. In addition chloride can be transported in the absence of sodium, but in the presence of sodium can be transported more rapidly than that ion. Chloride transport is to some extent linked to sodium transport and also to bicarbonate transport (AU)