Measurement of intracellular chloride ion concentration in ICC in situ and in explant culture.
BACKGROUND
Chloride channels are proposed to play a central role in the electrical pacemaking mechanism of interstitial cells of Cajal (ICC). A key unknown factor in the consideration of this role is the chloride equilibrium potential (E(Cl)), as determined by the relative concentrations of intra- ([Cl(-)](i)) and extracellular ([Cl(-)](o)) chloride ions.


METHODS
To calculate the E(Cl) of ICC, [Cl(-)](i) was measured with the fluorescent chloride indicator N-(6-methoxyquinolyl) acetoethyl ester (MQAE). Pacemaker ICC in explant cultures or in situ, i.e. ICC associated with the myenteric plexus of the small intestine, were loaded with MQAE and fluorescence was measured by laser scanning confocal microscopy. The dye fluorescence was then calibrated against known [Cl(-)](i) by treating the explants or in situ preparations with chloride ionophore and varying bath chloride concentrations.


RESULTS
In explants, ICC [Cl(-)](i) was measured as 13 mmol L(-1) with [Cl(-)](o) of 100 mmol L(-1), giving an E(Cl) of -52 mV [corrected]. With [Cl(-)](o) at 166 mmol L(-1), [Cl(-)](i) was 26 mmol L(-1), giving an E(Cl) of -47 mV[corrected]. In situ, ICC [Cl(-)](i) was measured as 26 mmol L(-1) with [Cl(-)](o) of 130 mmol L(-1), giving an E(Cl) of -41 mV [corrected]. Importantly ICC compensate for changes in extracellular chloride by changing [Cl(-)](i) and thus maintain E(Cl). In ICC explant clusters, [Cl(-)](i) was seen to fluctuate, possibly evoked by rhythmic changes in intracellular calcium.


CONCLUSIONS
The intracellular chloride concentration in ICC fluctuates to keep its equilibrium potential constant. The identification of E(Cl) as positive to the resting membrane potential of ICC indicates that opening of chloride channels will depolarize ICC.
Zhu
Y
Y
Farncombe Family Digestive Health Research Institute, McMaster University, Hamilton, ON L8N 3Z5, Canada.
Parsons
S P
SP
Huizinga
J D
JD
D000465:Algorithms; D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D002138:Calibration; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009197:Myenteric Plexus / Q000378:metabolism / Q000502:physiology*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011804:Quinolines
D018118:Chloride Channels; D002712:Chlorides; D005456:Fluorescent Dyes; D011804:Quinolines; C078229:N-(6-methoxyquinolyl)acetoethyl ester