Concomitant activation of Cl‐ and K+ currents by secretory stimulation in human epithelial cells.

Abstract

1. Whole-cell currents were investigated in the model salt-secreting epithelium, human T84 cell line, by means of the perforated patch-clamp technique. In the control extracellular medium containing Cl-, depolarizing voltage ramps evoked current responses which peaked at 5A43 + 0-81 pA pF-' at +60 mV and had a reversal potential (Erev) of -38-4 + 2-5 mV (n = 23).2. Activation of the cAMP pathway with forskolin increased the current at +60 mV from (n =6) and from 6-36 to 34-13 pA pF' (n = 4), respectively. With both agonists, Erev was shifted either towards the reversal potential for potassium, EK, or towards the reversal potential for chloride, Ecl, depending on the cell.4. In the absence of chloride ions (gluconate substituted), stimulation of the Ca2+ pathway activated a time-independent outward current of large amplitude. This current exhibited inward rectification at positive voltages, reverted at -89-5 + 0-2 mV and was markedly reduced by charybdotoxin (10 nM), a specific blocker of Ca2+-activated K+ channels. When a voltage step protocol was used, increased [Ca2+]i also activated an outward current at potentials more positive than -40 mV which slowly relaxed during depolarizing steps. 5. The activation of both (i) a time-independent inwardly rectifying charybdotoxinsensitive K+ current, and (ii) a time-dependent slowly inactivating current was also produced by cAMP stimulation. 6. We concluded that (i) in the T84 epithelial cells, both Cl-and K+ currents are concomitantly increased by secretagogue stimulation, and (ii) two different types of K+ conductances are activated by either the cAMP or the intracellular Ca21 secreting pathways.

Bradykinin-stimulated Cl - secretion in T84 cells. Role of Ca 2+ -activated hSK4-like K + channels

“…In the present study, the comparison of T84 wholecell currents at [Ca 2+ ] i of 10 and 100 nM reveals a large, Ca 2+ -activated, apparently voltage-independent, K + -selective whole-cell conductance, as has been reported previously [3]. The K + conductance in the present study was inhibited by Ba 2+ at the cytosolic but not at the extracellular membrane face (see Fig.…”

“…Furthermore, cAMP and Ca 2+ crossstimulation of the same K + conductance has been observed in T84 whole-cell experiments [3]. In addition, multiple consensus sites for phosphorylation by protein kinases A and C are present in the hSK4 protein [17].…”

β3-Adrenoceptor Control the Cystic Fibrosis Transmembrane Conductance Regulator through a cAMP/Protein Kinase A-independent Pathway

“…Current Recordings-Whole cell currents were recorded with the ruptured patch configuration of the patch-clamp technique as described previously (16). Cells were placed on the stage of an inverted microscope and bathed at 37°C in the same extracellular solution as used in SPQ experiments.…”

The antifungal antibiotic, clotrimazole, inhibits Cl- secretion by polarized monolayers of human colonic epithelial cells.

“…In separate studies using the whole cell perforated patch technique, two distinct K ϩ currents were identified in T84 cells. One K ϩ conductance was sensitive to charybdotoxin and the other was not sensitive to the toxin (23). The molecular identities of these K ϩ channels remain unknown.…”