The action of 5-hydroxytryptamine on normal and cystic fibrosis mouse colon: effects on secretion and intracellular calcium.
The ability of mouse colon to generate a secretory response to stimulation by 5-hydroxytryptamine (5-HT) was investigated in intact colonic sheets mounted in Ussing chambers. A preparation of intact isolated crypts was used to determine whether 5-HT action was associated with an elevation of cytosolic calcium levels, measured using the calcium-sensitive fluorescent dye, fura-2. 5-HT increased the short-circuit current, an effect that was inhibited by 55% in the absence of chloride and by 83% in the presence of serosal frusemide, consistent with the stimulation of electrogenic chloride secretion. This was confirmed by the observation that colonic tissue from transgenic cystic fibrosis mice (n = 4) failed to respond to 5-HT, although wild-type tissues generated an increased short-circuit current of 52.4+/-1.1 microAcm(-2) (n = 9). The electrical response to 5-HT was calcium-dependent. 5-HT action was unaffected by tetrodotoxin and was not mimicked by the 5-HT3 agonist 1-phenylbiguanide, indicating that neural mechanisms are not involved. The cyclooxygenase inhibitor indomethacin, however, reduced the 5-HT-induced rise in short-circuit current by 73%, suggesting that prostaglandin production contributes to the response. Stimulation of crypts with acetylcholine elicited an increase in cytosolic calcium levels, but no such response was detected on application of 5-HT (10(-6) to 10(-4) M), suggesting that 5-HT does not directly modulate intracellular calcium in colonic crypt cells. It is concluded that mouse colon responds to 5-HT challenge with a stimulation of electrogenic chloride secretion and that this effect is mediated by indirect mechanisms that might involve immune elements within the colonic wall.
Hardcastle
J
J
Department of Biomedical Science, University of Sheffield, UK.
Hardcastle
P T
PT
Klaren
P H
PH
Taylor
C J
CJ
White
S J
SJ
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003106:Colon / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D003550:Cystic Fibrosis / Q000235:genetics / Q000503:physiopathology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D005470:Fluorometry; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D012701:Serotonin / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology
D012701:Serotonin; D013779:Tetrodotoxin; D000109:Acetylcholine; D002118:Calcium; D007213:Indomethacin