Potassium Transport across the Distal Colon in Man

Abstract

1. The mechanism of potassium transport across human distal colon was investigated in twenty-two individuals without evidence of bowel disease, by using a dialysis method in conjunction with measurements of the transepithelial potential difference (p.d.). 2. Whether potassium was absorbed or secreted depended on its initial concentration in the lumen. The potassium net flux was approximately zero when the luminal potassium concentration was between 30 and 50 mmol/l. 3. Potassium secretion rate was little affected by sodium absorption rate, or by the luminal sodium concentration or by the osmolality of the luminal solution. 4. Potassium secretion rate was increased by partial substitution of other cations for sodium, in the descending order Li greater than NH4 greater than Rb greater than Na. Potassium concentration increased on average to over 80 mmol/l when lithium was in the lumen. 5. The observed transepithelial p.d. was inadequate to account for the intraluminal potassium concentrations attained, the discrepancy being most marked when ammonium or lithium was in the lumen. It is suggested that some potassium is secreted by the epithelial cells and this component of the total potassium flux into the lumen is increased when rubidium, ammonium or lithium is substituted for sodium.

Colonic potassium handling

“…Colonic mucosa from rodents on a normal diet display a slightly lumennegative (1-4 mV) transepithelial voltage (V te ) [36,71,78,134]. In in vivo studies in humans the recto-sigmoid V tes were measured and exceeded −35 mV [27,101]. In states of high plasma aldosterone, V te increases to higher lumennegative values, as a result of up-regulation of the epithelial Na + channel (ENaC) [27,36,78,134].…”

Pathways of Transepithelial Potassium Movement in the Epithelium of Distal Colon in Man

“…Thirty minutes before 43K was introduced, the distal part of the colon was rinsed three times with 20 ml of sodium chloride solution (150 mmol/l : saline) and all the solution completely ejected. A dialysis tube (Visking 8/32), of 7 mm diameter and 8 cm length and mounted on a rubber catheter containing a wire core for stiffening, was filled with about 2.5 ml of test solution (Edmonds, 1971;Salas-Coll et al, 1976). Solution 2 (Table 1) was used and also contained 20-35 MBq/l of 43K.…”

“…The essential details of the method with standard dialysis tubes (8 cm length) have been described before (Edmonds, 1971;Salas-Coll et al, 1976). In addition, some studies were made with a double dialysis tube comprising two lengths of dialysis tubing, each 4 cm long and mounted on a rubber catheter with a separation of about 1 -5 cm.…”

“…The concentration of the ion developed in faecal fluid is relatively high and appears greater than expected from the transepithelial electrochemical gradient (Wrong, Morrison & Hurst, 1961;Edmonds & Godfrey, 1970). Studies of human colonic epithelium, both in vivo and in vitro, have shown that considerable potassium secretion occurs (Salas-Coll, Kermode & Edmonds, 1976;Hawker, Mashiter & Turnberg, 1978), with the faecal potassium content and the epithelial secretion rate being markedly influenced by mineralocorticoid hormones and drugs (Shields, Mulholland & Elmslie, 1966;Charron, Leme, Wilson, Ing & Wrong, 1969;Richards, 1969;Tomkins & Edmonds, 1975). Moreover, in animal experiments it has been demonstrated that both high potassium intake and renal insufficiency lead to considerable increase in the potassium secretion rate (Fisher, Binder & Hayslett, 1976;Bastl, Hayslett & Binder, 1977).…”

The effect of lithium on the transport of sodium, potassium and chloride by the colon of normal and sodium‐depleted rats.

“…By contrast, in man, the p.d. tends to increase (Rask-Madsen, Baastrup & Schwartz, 1972; Salas-Coll, Kermode & Edmonds, 1976), and while Na absorption is unaffected and ims unchanged, the flux Jm of K is much increased so that there is considerable secretion of K with rise of K concentration in the lumen.…”