Hypotonic stress activates an intermediate conductance K+ channel in human colonic crypt cells.
OBJECTIVE
To investigate the effect of hypotonic stress on human colonic crypts cells in terms of ion channel activity and intracellular Ca2+ concentration.


METHODS
Single crypts were isolated from biopsies taken during colonoscopy. The patch clamp technique was used (in the cell-attached mode) to observe the activity of ion channels during hypotonic stress. Calcium measurements were made using the fluophores Fluo 3 or 4.


RESULTS
The intermediate conductance (29 pS), Ca2+ -sensitive, K+ channel (also known as KCNN4) previously described (Sandle et al. 1994) was seen in 54 of 149 patches (36%) when the crypts were bathed in normal extracellular solution (290 mOsm kg(-1)). Forty-one patches could be used for further analysis. Activation of one or several 29 pS channels was seen in 15 of 41 patches (39%) after 30 s to 4 min of exposure to hypotonic solution (160 mOsm kg(-1)). The open probability increased from 0.0043 in control solution to 0.44 at 5 min of hypotonic stress. When the crypts were exposed to hypotonic solution, an increase in intracellular Ca2+ could be seen. The increase in intracellular Ca2+ emanates mainly from intracellular stores.


CONCLUSIONS
The 29 pS K+ channel takes part in volume regulation in human colonic crypt cells. The activation of this channel is mediated through an increase in intracellular Ca2+.
Sand
P
P
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Anger
A
A
Rydqvist
B
B
D002118:Calcium / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D003106:Colon / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology*; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism* / Q000502:physiology
D007038:Hypotonic Solutions; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D024681:Potassium Channels, Calcium-Activated; D002118:Calcium