Heterogeneity of chloride channels in the apical membrane of isolated mitochondria-rich cells from toad skin.
The isolated epithelium of toad skin was disintegrated into single cells by treatment with collagenase and trypsine. Chloride channels of cell-attached and excised inside-out apical membrane-patches of mitochondria-rich cells were studied by the patch-clamp technique. The major population of Cl- channels constituted small 7-pS linear channels in symmetrical solutions (125 mM Cl-). In cell-attached and inside-out patches the single channel i/V-relationship could be described by electrodiffusion of Cl- with a Goldmann-Hodgkin-Katz permeability of, PCl = 1.2 x 10(-14) - 2.6 x 10(-14) cm3. s-1. The channel exhibited voltage-independent activity and could be activated by cAMP. This channel is a likely candidate for mediating the well known cAMP-induced transepithelial Cl- conductance of the amphibian skin epithelium. Another population of Cl- channels exhibited large, highly variable conductances (upper limit conductances, 150-550 pS) and could be activated by membrane depolarization. A group of intermediate-sized Cl(-)-channels included: (a) channels (mean conductance, 30 pS) with linear or slightly outwardly rectifying i/V-relationships and activity occurring in distinct "bursts," (b) channels (conductance-range, 10-27 pS) with marked depolarization-induced activity, and (c) channels with unresolvable kinetics. The variance of current fluctuations of such "noisy" patches exhibited a minimum close to the equilibrium-potential for Cl-. With channels occurring in only 38% of sealed patches and an even lower frequency of voltage-activated channels, the chloride conductance of the apical membrane of mitochondria-rich cells did not match quantitatively that previously estimated from macroscopic Ussing-chamber experiments. From a qualitative point of view, however, we have succeeded in demonstrating the existence of Cl-channels in the apical membrane with features comparable to macroscopic predictions, i.e., activation of channel gating by cAMP and, in a few patches, also by membrane depolarization.
Sørensen
J B
JB
August Krogh Institute, University of Copenhagen, Denmark. JBSorensen@aki.ku.dk
Larsen
E H
EH
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002023:Bufo bufo; D002462:Cell Membrane / Q000737:chemistry; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D004848:Epithelium / Q000737:chemistry / Q000648:ultrastructure; D007700:Kinetics; D008928:Mitochondria; D018408:Patch-Clamp Techniques; D011153:Population; D012867:Skin / Q000737:chemistry* / Q000166:cytology*
D018118:Chloride Channels; D000255:Adenosine Triphosphate; D000242:Cyclic AMP