Response of jejunal mucosa to electrical transmural stimulation and two neurotoxins

We examined the mucosal response to endogenous neurotransmitters released from enteric nerves of guinea pig jejunum in vitro by 5 s of electrical transmural stimulation (TS). After TS, a rise in short-circuit current (Isc) occurred that peaked by 60 s and returned to base line by 3-6 min. The Isc response was associated with Cl- movement toward the luminal side of the tissue. The use of adrenergic and muscarinic cholinergic antagonists revealed that there was no adrenergic component but that the cholinergic component comprised up to 50% of the total response. Therefore, more than 50% of the response was due to the action of nonadrenergic, noncholinergic transmitter(s). The addition of the neurotoxin, tetrodotoxin (TTX), produced two effects: 1) an early fall in the base-line Isc and increased net absorption of Na+ and Cl-, and 2) a delayed inhibition of the response to TS. The former effect occurred at lower concentrations of TTX than the latter. Another neurotoxin, aconitine, blocked the response to TS without decreasing the base-line Isc or altering net ion transport. After aconitine, TTX still caused the Isc base line to fall. Because both neurotoxins prevented the Isc response to TS, we conclude that the response is due to the action of released endogenous neurotransmitters. Our results also suggest that TTX has an additional effect that is different from that of aconitine, acting either on the epithelium to enhance absorption or on a population of nerves that are relatively more TTX sensitive to block ongoing release of secretion-stimulating transmitter(s).