apical and serosal k+ channels in larval insect midgut
TRANSCRIPT
836 Abstracts
EF 28 BUMETANIDE BINDING To THE PAROTID NaCl/KCl CCITRANSPORTER. R.J. Turner and J.N. George, NIDR, NIH, Bethesda MD, U.S.A.
Bumetanide (BUM) binding to the rabbit paro- tid NaCl/KCl cotransport obeyed Michelian kinetics indicating the existence of a single binding site with KD = 3 ,uM. Binding was a hyperbolic function of [Na] and [K] with K = 33 mM and 23 mM, respectively at 5 mM e15 The dependence on [Cl] was biphasic, with binding increasing from O-5 mM Cl and decrea- sing thereafter. This latter observation in- dicates the presence of at least two Cl sites associated with BUM binding, the first a high affinity stimulatory site and the second a lower affinity inhibitory site possibly the BUM binding site itself. The Triton X-100 solubilized binding site retained its capaci- ty to bind BUM as well as its dependence on Na, K and Cl, but the BUM KD decreased to 0.3 DM, a value more consistent with the BUM binding characteristics of other tissues (e.g., renal medulla). This may indicate that the NaCl/KCl cotransporter is found in a mar- kedly different membrane environment in the protid than in these other tissues.
EF 30 Cl TRANSPORT IN NORMAL (NL) AND CYSTIC FIBRO- SIS (CF) CULTURED HUMAN NASAL EPITHELIUM (HNE). N.J. Willumsen and R.C. Boucher, Univ. of North Carolina, Chapel Hill, USA.
Intracellular Cl activity (aC1) was measured with double barreled Cl-selective microelec- trodes in cultured NL and CF HNE. Baseline aC1 was similar in Nt (42.7k2.0 mM, n=34) and CF (46.5+2.5 mM, n=28). However, due to dif- ferent apical membrane (AM) potentials, Cl was in equilibrium across the AM in normals but below equilibrium in CF. For both CF and NL, aC1 was above equilibrium across the ba- solateral membrane (BLM) and aC1 was de- creased by bumetanide. Luminal [Cl] reduction (120 to 3 mM) depolarized the AM and reduced aC1 in NL (42.7t4.0 to 27.Ok3.5 mM, n=ll); no effects were detected in CF. Reduction of serosal [Cl] (120 to 3 mM) led to a rapid (80s) depolarization of the BLM potential and to a prolonged 030 min) decrease in aC1 in both NL (45.5k2.5 to 31.1k4.2 mM, n=8) and CF (58.Ok6.7 to 26.Q2.9 mM, n=7). In both NL and CF the decrease in aC1 was markedly in- hibited by bumetanide. We conclude that the AM Cl permeability is reduced in CF whereas the conductive and bumetanide sensitive paths in the BLM are not affected by CF.
EF 29 OPERATION OF K+ AND Cl- CHANNELS IN CULTURED RAT PARIETAL CELLS UPON THE STIMULATION WITH ACID SECRETAG%UES. s. Ueda, T. Kotera and Y. Okada, Dept. of Internal Medicine, and Dept. of Physiology, Faculty of Medicine, Kyoto Univ. Kyoto 606, Japan.
Upon the stimulation with putative gastric acid secretagogues, fluorescence of Acridine Orange and that of quin 2 were found to in- crease within the monolayer parietal cells which were identified in the organ culture of fragmented gastric fundus of newborn rats. Electrophysiological studies by conventional intracellular recordings and giga-seal single ch2yel recordiqgs indicated that no$+only Ca -activated K channels but also Ca -in- dependent Cl- channels are operating during receptor-mediated activation of parietal cells.
EF 31 APICAL AND SEROSAL K+ CHANNELS IN LARVAL INSECT MIDGUT. W. Zeiske and H. Schroder, Inst. Tierphysiol, Freie Univ, Berlin, D.
Manduca sexta midgut actively selretes K+ along serosal channels and apical K -ATPase. This-report deals with serosal anion stimula- tion and, in addition, apical K channels. Exchanqinq bath Cl bv Glu reduces outward current, i , and unspeci%c conductance I.. recover!! uuicklv with halides but no; S%’ OF NO- while-G is-restored with all. I turat& but wieh Cl-,
sa- a proportional in&ease
ofK andI as well as slight deviation fromm MM-ki#%ics are seen. Furosemide inhi- bits I with either anion. Thus, serosal K+ channe s r display features of KC1 cotranspor- ters, with respect to halogen ion and blocker effects. A large, serosally-directed (K+)-
graS! ient elicits a small inverse I . Mucosal Ba ions reduce this current &ile gener- ating typical blocker tion of these apical at present.
nqise. Site and -func- K channels are obscure