title: Current-noise analysis of the basolateral route for K+ ions across a K+-secreting insect midgut epithelium (Manduca sexta).
abstract: The isolated midgut of a lepidopteran larva (Manduca sexta), 5th instar was investigated with voltage-clamp and fluctuation analysis techniques. With high K+ insect saline on both sides the outward-directed short-circuit current (Isc) was carried by K+ (IK) from serosal to mucosal compartment. IK could be blocked, in a dose-dependent manner by serosal Ba2+ ions. There was no current with serosal Na+. Noise analysis of IK revealed a Lorentzian component in the power spectrum when Ba2+ was present in the serosal solution. The Ba2+/receptor kinetics show pseudo-first order characteristics only at low [Ba2+]s. For [Ba2+]s greater than KBa, the apparent Ba2+ association rate decreases with a hyperbolic course as a function of serosal [Ba2+] which could indicate some "substrate-inhibition"-like interaction of Ba2+ at its receptor site. It is concluded that the serosal membranes of the K+-secreting intestinal cells contain the common type of Ba2+-blockable K+ channel which provides the serosal pathway for K+ during secretion which is ultimately driven by the mucosally-located electrogenic K+-ATPase.
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D001692:Biological Transport; D004848:Epithelium / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D007473:Ion Channels / Q000502:physiology*; D007814:Larva / Q000502:physiology; D007915:Lepidoptera / Q000502:physiology*; D008433:Mathematics; D008564:Membrane Potentials; D008954:Models, Biological; D011188:Potassium / Q000502:physiology*; D013997:Time Factors
chemical_list: D007473:Ion Channels; D001464:Barium; D011188:Potassium