Ion channels in basolateral membrane of marginal cells dissociated from gerbil stria vascularis.
The basolateral membrane of isolated strial marginal cells has been probed for conductive pathways by the patch-clamp technique. Two types of voltage-insensitive channels were identified in both cell-attached and excised patches. Of these, frequently (69% of excised patches) observed was a Ca(2+)-activated nonselective cation channel having a unit conductance of 24.9 +/- 0.5 pS (N = 16). Other characteristics of this type in excised patches include: 1) linear I-V relations with 150 mM K+ (pipette)/150 mM Na+ (bath), 2) a permeability sequence of NH4+ > Na+ = K+ = Rb+ > Li+, 3) a flickering block by quinine or quinidine (both 1 mM), and 4) a dose dependent block of its activity by ADP or ATP (IC50,ATP/IC50,ADP = 20-35), both from the cytosolic side. Channels with similar characteristics were found in the apical membrane of the same cell; however, the basolateral channels were 2-4 times more densely distributed than the apical counterparts. Also frequently (57%) detected was a Cl- channel of 80.0 +/- 0.5 pS (N = 6), whose activity was Ca2+ independent. Additionally, this Cl- channel had: 1) linear I-V relations with symmetric Cl-, 2) a permeability sequence of Cl- > Br- > I- > or = NO3- > or = gluconate-, and 3) a complete and reversible block by 1 mM diphenylamine-2-carboxylate. In contrast to the apical Cl- channels, the basolateral ones had a much higher density (57% vs. < 1%) as well as a higher unit conductance (80 pS vs. 50 pS) than the apical counterpart. The relative abundance of these two types as the major conductive pathways for Na+, K+, and Cl- in the basolateral region must be taken into account when addressing the role of strial marginal cells in generating the positive endocochlear potential. The Cl- channel may facilitate Cl- distribution across the basolateral membrane.
Takeuchi
S
S
Department of Physiology, Kochi Medical School, Nankoku, Japan.
Ando
M
M
Kozakura
K
K
Saito
H
H
Irimajiri
A
A
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001965:Bromides / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D005849:Gerbillinae; D007454:Iodides / Q000378:metabolism; D007473:Ion Channels / Q000502:physiology*; D008433:Mathematics; D008854:Microscopy, Electron; D009566:Nitrates / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013316:Stria Vascularis / Q000166:cytology* / Q000187:drug effects / Q000648:ultrastructure
D001965:Bromides; D002712:Chlorides; D007454:Iodides; D007473:Ion Channels; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D012413:Rubidium; D011188:Potassium; D002118:Calcium