Effects of the gaseous signalling molecule nitroxyl (HNO) on myenteric neurons governing intestinal motility

The main function of myenteric neurons is the control of gut motility. As we recently showed that nitroxyl (HNO) induces intestinal smooth muscle relaxation, it was of interest to evaluate the effects of this signalling molecule on myenteric neurons in order to distinguish its properties in regard to myocytes.

Myenteric neurons isolated from the ileum of 4-10 days old rats were used. HNO-induced changes in intracellular concentration of Ca²⁺ or membrane potential and ion currents were measured using the Ca²⁺-sensitive fluorescent dye fura-2 AM or by electrophysiological whole-cell recordings, respectively. Changes in intracellular thiol groups pool were evaluated using thiol tracker violet. Angeli's salt was used as HNO donor.

The HNO donor Angeli's salt induced a significant increase in the cytosolic Ca²⁺ concentration at the concentration 50 µM and a membrane hyperpolarization from a resting membrane potential of -56.1 ± 8.0 mV to -63.1 ± 8.7 mV (n=7). Although potassium channels primarily drive membrane potential changes in these cells, outwardly rectifying potassium currents were not significantly affected by 50 µM Angeli's salt. Fast inward sodium currents were slightly but not significantly reduced by HNO. In more sensitive cells, HNO tended to reduce the pool of thiol groups.

As in the case of smooth muscle cells, HNO causes hyperpolarization of myenteric neurons, an effect also associated with an increase in intracellular Ca²⁺ concentration. Pathways other than activation of potassium currents appear to drive the hyperpolarization evoked by HNO.