ISSN:
1432-1424
Keywords:
Na,K-ATPase
;
vanadate
;
rubidium
;
shark rectal gland
;
ouabain
;
cAMP
;
theophylline
;
furosemide
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Scatchard analysis of3H ouabain bound to isolated rectal gland cells as a function of increasing ouabain concentrations produced a concave curvilinear plot that was resolved into two specific sites with either a high (I) or low (II) affinity for ouabain. Cyclic cAMP/theophylline (±furosemide, 10−4 m) increased the amount of3H ouabain bound to the high-affinity site I. Vanadate, a phosphate congener which promotes formation of the ouabain-binding state of the enzyme, mimicked the effects of cAMP/theophylline at low concentrations of ouabain, suggesting that cAMP/theophylline increases binding to site I by enhancing the rate of turnover of resident enzyme. Enhanced86Rb uptake seen following cAMP/theophylline administration was primarily associated with increased flux through the high-affinity ouabain site, and this stimulation was not obliterated by the co-administration of furosemide. A model was presented which suggested the presence of two noninteracting pools of enzyme or isozymes which exhibit either a high or low affinity for ouabain. Cyclic AMP both stimulated turnover via site I, and modified the kinetics of binding of3H ouabain to site II. The (ave)K d of3H ouabain for site II was increased from 3.6 μm (controls) to 0.5 μm (cAMP/theophylline) and the Hill coefficient was modified from 0.45 (controls) to 1.12 (caMP/theophylline), suggesting a transition from a negative- to a noncooperative binding state. While furosemide reversed the effects of cAMP/theophylline on site II kinetics, it did not obliterate cAMP/theophylline effects on site I. This suggests that cAMP may alter the intrinsic turnover rate of this particular pool of Na,K-ATPase in shark rectal gland.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01869716
