Amiloride-sensitive cationic channels are present in the apical membrane of porcine thyroid cells in primary culture. An amiloride-sensitive (K0.5= 150 ± 28 nM where K0.5 is the concentration of unlabelled ligand which reduces the specific binding of the same labelled ligand by 50%) 22Na+-flux component (Km for Na+ at 18 mM) has been identified which was also blocked by the potent amiloride derivative phenamil (K0.5= 47 ± 21 nM). The most potent inhibitor of Na+/H+ exchange, ethylisopropyl-amiloride, hardly inhibited this 22Na+-influx component at a concentration of 21 μM. Amiloride binding sites were characterized using [3H]phenamil. The tritiated ligand binds to a single family of binding sites in thyroid membranes with a Kd value of 50 ± 10 nM and a maximal binding capacity of 5 ± 1 pmol/mg protein. Patch-clamp experiments have directly demonstrated the existence of a phenamil- and amiloride-sensitive cationic channel, with a conductance of 2.6 pS, which is permeable to sodium, but not very selective (PNa-/PK+= 1.2). This channel is an important element in the regulation of the resting membrane potential of thyroid cells.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.
the concentration of unlabelled ligand which reduces the specific binding of the same labelled ligand by 50%