AJP - Cell Physiology, Vol 249, Issue 1 129-C139, Copyright © 1985 by American Physiological Society
Greater ATP dependence than sodium dependence of radiocalcium efflux in bullfrog ventricle
G. Brommundt and F. Kavaler
45Ca efflux was studied in intact bullfrog ventricles following a 2-h
period of loading with radiocalcium-containing Ringer solution. The
cannulated ventricle was placed in a closed air-filled container to which
were applied rhythmic, electronically timed, positive- and
negative-pressure pulsations, which induced ventricular volume excursions.
The mechanical arrangement and timing circuitry made it possible for each
period to be as short in duration as 15 s. By use of this technique,
penetration of the extracellular space by [14C]inulin was found to be
complete within 30 s, and recovery of the inulin proceeded with a time
constant of 17-24 s, indicating a completeness of recovery of 98% within 90
s. Washout of added 45Ca was quantitatively quite close to that of inulin,
and in addition the estimated rate of sequestration of the isotope was slow
enough to introduce only a small error into the experimental results. 45Ca
efflux was only slightly (15%) sensitive to replacement of extracellular
sodium but was profoundly sensitive to the inhibitors of ATP synthesis,
cyanide and 2-deoxy-glucose.
