title: A cation channel in frog lens epithelia responsive to pressure and calcium.
abstract: Patch-clamp recording from the apical surface of the epithelium of frog lens reveals a cation-selective channel after pressure (about +/- 30 mm Hg) is applied to the pipette. The open state of this channel has a conductance of some 50 pS near the resting potential (-56.1 +/- 2.3 mV) when 107 mM NaCl and 10 HEPES (pH 7.3) is outside the channel. The probability of the channel being open depends strongly on pressure but the current-voltage relation of the open state does not. With minimal Ca2+ (55 +/- 2 microM) outside the channel, the current-voltage relation is nonlinear even in symmetrical salt solutions, allowing more current to flow into the cell than out. The channel, in minimal Ca2+ solution, is selective among the monovalent cations in the following sequence K+ greater than Rb+ greater than Cs+ greater than Na+ greater than Li+. The conductance depends monotonically on the mole fraction of K+ when the other ion present is Li+ or Na+. The single-channel current is a saturating function of [K+] when K+ is the permeant ion, for [K+] less than or equal to 214 mM. When [Ca2+] = 2 mM, the current-voltage relation is linearized and the channel cannot distinguish Na+ and K+.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D007908:Lens, Crystalline / Q000187:drug effects / Q000502:physiology*; D011312:Pressure; D011892:Rana catesbeiana; D011894:Rana pipiens; D014981:Xenopus
chemical_list: D007473:Ion Channels; D002118:Calcium