Inhibition by barium and glibenclamide of the net loss of 86Rb+ from rabbit myocardium during hypoxia.
OBJECTIVE
The aim was to determine the effects of barium ions and glibenclamide on the hypoxia induced K+ efflux from rabbit myocardium.


METHODS
Experiments were performed on the isolated interventricular septum of the rabbit perfused with a physiological solution through the septal artery. The stimulation rate was 90 beats.min-1 and the temperature 32 degrees C. The flux of 86Rb+ was used as a surrogate of K+ fluxes.


METHODS
Septa were obtained from adult male New Zealand white rabbits.


RESULTS
The uptake of 86Rb+ by the septum could be fitted to a single exponential curve with a rate constant of 0.024(SEM 0.001) min-1 (n = 14). Washout experiments were performed in which septa were labelled with 86Rb+ and then perfused with unlabelled solution for 60 min. The rate constants for the efflux of 86Rb+ were similar and were 0.022(0.001) min-1 (n = 13) for radioactivity in the tissue and 0.029(0.001) min-1 (n = 13) for radioactivity in the effluent. These rate constants were similar to those reported previously for 42K+. Septa were labelled for 150 to 180 min with 86Rb+ and then perfused with a hypoxic substrate free solution for 15 min followed by reoxygenation. The net loss of 86Rb+ was calculated to be equivalent to 4.00(0.20) mmol.kg-1 wet tissue of K+ (n = 8) and in washout experiments (n = 6) this loss was shown to be due to increased efflux. Ba2+, 0.1 mM and 1.0 mM, added at the onset of hypoxia decreased net tissue loss of 86Rb+ by 64(6)% (n = 5) and 97(1)% (n = 6) respectively (both p less than 0.01). Glibenclamide (0.1 mM) decreased tissue net loss by 52(3)% (n = 6, p less than 0.01).


CONCLUSIONS
Part of hypoxia induced net K+ loss in this preparation can be attributed to activation of ATP sensitive K+ channels but other mechanisms are also involved.
Jiang
C
C
National Heart and Lung Institute, London, United Kingdom.
Crake
T
T
Poole-Wilson
P A
PA
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009924:Organ Culture Techniques; D010100:Oxygen / Q000502:physiology*; D010477:Perfusion; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects; D011817:Rabbits; D012414:Rubidium Radioisotopes
D015221:Potassium Channels; D012414:Rubidium Radioisotopes; D001464:Barium; D011188:Potassium; D010100:Oxygen; D005905:Glyburide