Effects of tetrodotoxin on chloride secretion in rabbit distal colon: tissue and cellular studies.
The effects of tetrodotoxin (TTX) were examined in muscle-stripped segments of rabbit distal colon and in cells of isolated colonic crypts. Electrical field stimulation (EFS) of the submucosa/mucosa evoked an increase in short-circuit current (ISC) that was due to an increase in chloride secretion. The EFS-evoked response was reduced 81% by 10(-7) M TTX and 30% by 5 X 10(-6) M atropine. Vasoactive intestinal peptide (VIP), carbachol, aminophylline, and 1,1-dimethyl-4-phenylpiperazinium increased ISC. Bumetanide reduced the responses to neural stimulation, aminophylline, and VIP. To determine whether TTX had direct effects on crypt epithelial cells, crypts were isolated and cells were impaled with microelectrodes. Mean resting potential (Vbl) was -67 +/- 1.1 mV (n = 63). VIP and aminophylline depolarized Vbl by 34 +/- 4.6 (n = 13) and 34 +/- 3.5 mV (n = 18), respectively. TTX had no significant effect on resting Vbl or on the responses to VIP or aminophylline. We conclude that stimulation of submucosal neurons in the rabbit distal colon evokes a TTX- and bumetanide-sensitive increase in net chloride secretion that is dependent on the release of acetylcholine and other secretory neurotransmitters. Electrophysiological studies rule out a direct effect of TTX on colonic crypt cells.
Biagi
B
B
Department of Physiology, Ohio State University, Columbus 43210.
Wang
Y Z
YZ
Cooke
H J
HJ
D000584:Amiloride / Q000494:pharmacology; D000628:Aminophylline / Q000494:pharmacology; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000187:drug effects / Q000502:physiology*; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004553:Electric Conductivity; D004558:Electric Stimulation; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D011817:Rabbits; D013779:Tetrodotoxin / Q000494:pharmacology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D002712:Chlorides; D002034:Bumetanide; D000628:Aminophylline; D014660:Vasoactive Intestinal Peptide; D013779:Tetrodotoxin; D004246:Dimethylphenylpiperazinium Iodide; D000584:Amiloride; D002217:Carbachol