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BAFILOMYCIN A₁ AT NANOMOLAR CONCENTRATIONS SATURABLY INHIBITS A PORTION OF TURTLE BLADDER ACIDIFICATION CURRENT

STEVEN J. YOUMANS^* and CATHERINE R. BARRY

Department of Physiology, New York College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, Long Island, NY 11568-8000, USA
^* Author for correspondence (e-mail: syoumans{at}iris.nyit.edu )

View larger version (15K): [in a new window]   Fig. 1. Effect of bafilomycin A1 exposure on acidification current. Separate experiments are shown in A and B. In both experiments, turtle bladders were mounted in Ussing chambers as described in Materials and methods and exposed to 0.2 mmol l-1 ouabain in the serosal solution (arrow) to eliminate sodium transport. When the short circuit current (acidification current) subsequently reached a new steady state, the bladder was exposed to either 5 nmol l-1 bafilomycin A1 in the serosal bathing solution (A) or to a graded sequence of bafilomycin A1 concentrations in the mucosal solution (B; final concentrations are shown in nmol l-1). Baf, bafilomycin A1. Short circuit current shown is in µA (per area of chamber, 1.43 cm2). The unlabeled number in the lower right of each panel is an index number identifying the experiment.

View larger version (14K): [in a new window]   Fig. 3. Effects of bafilomycin A1 and Sch-28080 on acidification current in a representative experiment. The bladder was maintained in an Ussing-type chamber and conditions were as described for Fig. 1. Baf, bafilomycin A1 (5x10-9 mol l-1, mucosal); Sch, Sch-28080 (3x10-5 mol l-1, mucosal) were introduced where indicated (arrows).

View larger version (16K): [in a new window]   Fig. 2. Effect of bafilomycin A1 on acid secretion by intact turtle bladders. Dose—response inhibition curve. Turtle urinary bladders were mounted in Ussing-type chambers and bathed in Na/Cl/HCO3 Ringer's solution. The serosal solution contained 0.2 mmol l-1 ouabain. Under these conditions the short-circuit current across the tissue approximates the rate of net acid-base transport and is typically oriented serosal-side negative (acid secretion; see Materials and methods). Baseline acid secretion (100 %) was -12.0±4.3 µA (per area of chamber, 1.43 cm2) (N=4). Bafilomycin A1 in DMSO vehicle was added in the luminal solution to the concentrations indicated and the short-circuit current allowed to stabilize after each addition. The final concentration of DMSO never exceeded 0.3 %.

View larger version (13K): [in a new window]   Fig. 4. Inhibition of acid secretion by bafilomycin A1 and Sch-28080. Urinary bladders were mounted in vitro in chambers as described in Materials and methods and the legend to Fig. 1. When the short-circuit current was stable, bafilomycin A1 was introduced into the mucosal solution to the indicated final concentration. When the short-circuit current again stabilized, Sch-28080 was then added to the mucosal solution to the concentration indicated. Bars show inhibition by each compound as a percentage of baseline acid secretion (-4.7±1.25 µA (per area of chamber, 1.43 cm2), N=7). *Significant effect of treatment (P<0.01).