Cation-selective channels in amphibian epithelia: electrophysiological properties and activation.
1. Na+ as well as Li+ move across the apical membrane through amiloride-sensitive ionic channels. 2. K+ movements across the apical membrane occur through Ba2+- and Cs+-sensitive channels which do not allow the passage of Na+ or Li+. 3. A third pathway in the apical membrane is permeable for Na+, K+, Cs+, Rb+, NH+4 and Ti+. The currents carried by these monovalent cations are blocked by Ca2+ and divalent cations as well as La3+. 4. In the urinary bladder, the Ca2+-sensitive currents are stimulated by oxytocin, activators of cytosolic cAMP and cAMP analogues. Also the oxytocin activated currents are blocked by divalent cations and La3+. 5. Nanomolar concentrations of mucosal Ag+ activate the third channel and open the pathway for movements of Ca2+, Ba2+ and Mg2+, which are known to permeate through Ca2+ channels in excitable tissues.
Van Driessche
W
W
Laboratorium voor Fysiologie, KUL, Campus Gasthuisberg, Belgium.
Simaels
J
J
Aelvoet
I
I
Erlij
D
D
D000818:Animals; D001692:Biological Transport; D002412:Cations / Q000378:metabolism*; D007473:Ion Channels / Q000502:physiology*; D011896:Rana temporaria; D012867:Skin / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism
D002412:Cations; D007473:Ion Channels