Electrical Conductivity and Cholinergic Activity of the Rat Gastric Mucosa, At 4 and 170 Hours after 600 R X-Irradiation

Gastric mucosas were prepared for incubation from excised whole stomachs of irradiated and nonirradiated rats. Measurements were made of transmucosal potential, direct current conductivity, and acetylcholine (ACh) response. When suitably prepared, the mucosa showed low conductivity values of $12\ {\rm mmho}/{\rm cm}^{2}$. Conductivity increased markedly after imposing brief electric shock $8\ {\rm mA}/{\rm cm}^{2}$ or after metabolic inhibition (nitrogen). The response, in both cases, was like a depolarization, with the potential decreasing concomitantly. After irradiation, a different type of response occurred after 4 hours and after 170 hours. After 4 hours, the potential was elevated 40% above that of the nonirradiated control, with negligible change in conductivity. No significant change was detected in reactivity toward 10-3 M ACh (added to the baths). After 170 hours, the potential was identical to that of the nonirradiated control, but conductivity showed a consistent increase of about 17%. In these cases, 10-3 M ACh caused a more rapid inhibition of potential. ACh had no effect on conductivity in either radiation group. Analysis of the 4-hour data indicated that the acute effect of radiation was to inhibit cholinergic effector activity without affecting ACh receptor sites. In the 170-hour group, cholinergic effector activity had returned to normal, but irradiation had left the mucosa both more permeable to ions (i.e., increased conductivity) and with increased sensitivity of the ACh receptor sites.