Basolateral K channels in an insect epithelium. Channel density, conductance, and block by barium.
K channels in the basolateral membrane of insect hindgut were studied using current fluctuation analysis and microelectrodes. Locust recta were mounted in Ussing-type chambers containing Cl-free saline and cyclic AMP (cAMP). A transepithelial K current was induced by raising serosal [K] under short-circuit conditions. Adding Ba to the mucosal (luminal) side under these conditions had no effect; however, serosal Ba reversibly inhibited the short-circuit current (Isc), increased transepithelial resistance (Rt), and added a Lorentzian component to power density spectra of the Isc. A nonlinear relationship between corner frequency and serosal [Ba] was observed, which suggests that the rate constant for Ba association with basolateral channels increased as [Ba] was elevated. Microelectrode experiments revealed that the basolateral membrane hyperpolarized when Ba was added: this change in membrane potential could explain the nonlinearity of the 2 pi fc vs. [Ba] relationship if external Ba sensed about three-quarters of the basolateral membrane field. Conventional microelectrodes were used to determine the correspondence between transepithelially measured current noise and basolateral membrane conductance fluctuations, and ion-sensitive microelectrodes were used to measure intracellular K activity (acK). From the relationship between the net electrochemical potential for K across the basolateral membrane and the single channel current calculated from noise analysis, we estimate that the conductance of basolateral K channels is approximately 60 pS, and that there are approximately 180 million channels per square centimeter of tissue area.
J W
JW
Hanrahan
N K
NK
Wills
J E
JE
Phillips
S A
SA
Lewis
D000818:Animals; D001464:Barium / Q000494:pharmacology; D004553:Electric Conductivity; D004563:Electrochemistry; D004848:Epithelium / Q000378:metabolism; D006110:Grasshoppers; D007413:Intestinal Mucosa / Q000378:metabolism*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*
D007473:Ion Channels; D001464:Barium; D011188:Potassium