AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 1 76-R83, Copyright © 1992 by American Physiological Society
Ion transport by the isolated mantle epithelium of the freshwater clam, Unio complanatus
R. L. Hudson
Department of Physiology and Biophysics, College of Medicine, University of Illinois, Chicago 60680.
Transepithelial ion transport was studied in three types of shell-facing
mantle epithelia of the freshwater clam, Unio complanatus. These were 1)
the epithelium isolated from near the margin of the shell; 2) the
epithelium from the central region of a "normal" shell; and 3) the
epithelium from the central region that was regenerating a damaged shell.
Marginal and "shell-regenerating" epithelia produced a small (less than 5
mV) transepithelial voltage that was independent of PCO2 (0-4%). In the
presence of 4% PCO2, the "normal" central epithelium produced a
significantly larger transepithelial voltage (-8.5 +/- 0.99 mV), that, in
addition, could be stimulated (-30.5 +/- 2.18 mV) by permeable analogues of
adenosine 3',5'-cyclic monophosphate (cAMP) [e.g.,
8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate]. Voltage
clamping the transepithelial voltage to zero resulted in a short-circuit
current (Isc) that was consistent with positive charge moving from the
hemolymph toward the shell. The measurements of transepithelial fluxes of
45Ca, 22Na, 42K, and 36Cl revealed that none of these ions, alone or in
combination, could account for the stimulated Isc in "normal" mantle. In
addition, similar measurements in marginal and "shell-regenerating"
epithelia did not detect any significant net transepithelial flux of any of
these ions. Acid extrusion at the shell-facing membrane and bicarbonate
extrusion at the hemolymph-facing membrane were identified in "normal"
central epithelium, but could not be found in marginal or
"shell-regenerating" epithelia. These fluxes are equivalent to the
cAMP-stimulated Isc in "normal" central epithelium.(ABSTRACT TRUNCATED AT
250 WORDS)
