P-chloromercuribenzene sulfonate blocks and reverses the effect of amiloride on sodium transport across rabbit colon in vitro.

The addition of 10(-3) M p-chloromercuribenzene sulfonate (PCMBS) to the solution bathing the mucosal surface of rabbit colon has no effect on the rate of active Na transport but blocks or reverses the inhibitory action of amiloride. The tissue must be exposed to PCMBS for 20-30 min for a complete blocking effect, and removal of PCMBS from the mucosal solution after this period of exposure does not restore the sensitivity of the tissue to amiloride. The slow time-courses of the blocking and reversal effects suggest that PCMBS does not irreversibly interact with groups directly involved in the binding of amiloride.