Apical and basolateral membrane ionic channels in rabbit urinary bladder epithelium.

This paper reviews the properties and regulation of single amiloride-sensitive Na+ channels in the apical membrane, and Cl- and K+ channels in the basolateral membrane of rabbit urinary bladder. According to fluctuation analysis, there is an average of one amiloride-sensitive Na+ channel for every 40 micron2 of apical membrane. Each Na+ channel passes 0.7 pA of current under normal, short-circuit conditions. Apical channels are hydrolysed by the endogenous enzyme urokinase, which is released into the urine by the kidney. After exposure to urokinase, the Na+ channel loses its amiloride sensitivity, and eventually becomes unstable in the membrane. The selectivity and kinetic properties of single anion and K+ channels in the basolateral membrane were also studied using the patch clamp technique. The properties of these channels are discussed in terms of the regulation of transepithelial Na+ transport.