AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 1 91-R94, Copyright © 1983 by American Physiological Society
Active transport of calcium across the urinary bladder and colon of the toad Bufo marinus
C. J. Rosoff, G. F. Baldwin and P. J. Bentley
Unidirectional fluxes of calcium were measured (in vitro) across the
urinary bladder and colon of the toad Bufo marinus in the absence of
electrochemical gradients. A net calcium flux was observed in each tissue,
but the polarity differed; it occurred from the mucosal (luminal) to the
serosal side of the colon and from the serosal to mucosal (urinary) side of
the bladder. The active transport in each tissue appeared to involve
different mechanisms; that across the colon exhibited a sodium dependence,
possibly involving a sodium-calcium exchange, but this was not seen in the
urinary bladder. The net flux in the latter was, however, abolished by
metabolic inhibitors, possibly reflecting a role of a calcium-adenosine
triphosphatase mechanism. The results are discussed in relation to the
calcium metabolism of this amphibian.
