An upper limit to the number of sodium channels in frog skin epithelium.

1. Binding of [(14)C]amiloride to the mucosal surface of frog skin epithelium has been measured in the presence and absence of an excess of unlabelled amiloride. Simultaneous records were obtained of the sodium transport through the skin as indicated by the short circuit current.2. The number of binding sites with affinities for amiloride of 5 x 10(7) l./mole was around 400/mum(2).3. The relation between the binding sites and sodium channels is discussed.4. Making certain assumptions it is concluded that when frog skin epithelium is bathed in Ringer solution each sodium channel can handle 8000 sodium ions/sec.