Movement of thallium (I) ions in vitro.

1. Movement of thallium (I) ions across the mucosal epithelium of descending rat colon, stripped of the muscularis externa in vitro was determined under voltage clamp conditions. 2. The unidirectional fluxes of thallium (I) ions from mucosal to serosal side (M leads to S) and in the opposite direction (S leads to M) were measured at 0 mV. A net flux of thallium (I) ions was observed from serosal to mucosal side (0.216 nmoles . cm-2 . h-1) in other words, the mucosal epithelium is apparently asymmetric for the movement of thallium (I) ions. 3. The investigations were carried out on the range of -30mV up to +30 mV from mucosal to serosal side. Thallium (I) ions move from mucosal to serosal side (M leads to S) by diffusion only (Pi = 0.119 cm.h-1), whereas into the opposite direction (S leads to M) thallium (I) ions in addition to a voltage-dependent component are transported against an electrical gradient.