Identification and properties of a novel type of Na+-permeable amiloride-sensitive channel in thyroid cells.
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 microM. 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.
Verrier
B
B
Unité 270 de l'Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine Secteur Nord, Marseille.
Champigny
G
G
Barbry
P
P
Gerard
C
C
Mauchamp
J
J
Lazdunski
M
M
D000584:Amiloride / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013552:Swine; D013961:Thyroid Gland / Q000378:metabolism*
D015222:Sodium Channels; C047088:phenylamil; D000584:Amiloride; D012964:Sodium