Loop diuretics may fail to inhibit (Na+, K+, Cl-) 'cotransport' in human red cells.

The inhibition of passive K+ influx into human red blood cells (RBC) by loop diuretics was found to be dependent on the external Na+ concentration. In the absence of external Na+, there was minimal inhibition but the influx remained dependent on Cl- ions. Thus, raising the external Na+ concentration increased the affinity of the putative (Na+, K+, Cl-) cotransport system in human RBC for loop diuretics.