AJP - Renal Physiology, Vol 256, Issue 4 590-F595, Copyright © 1989 by American Physiological Society
Variability of cellular responsiveness to ADH stimulation in toad urinary bladder
W. A. Kachadorian, J. Muller and V. A. DiScala
Laboratory of Cardiovascular Science, National Institute on Aging, Baltimore 21224.
The hydrosmotic response of toad bladder to antidiuretic hormone (ADH) is
quantitatively linked to the induced fusion of aggrephores with, and the
appearance of aggregates of tightly packed intramembrane particles in the
luminal membrane of granular cells. We used these morphological indexes of
hormonally induced cell activation 1) to assess the variability of
individual cell responsiveness to a maximally stimulating concentration of
ADH and 2) to compare cell response patterns in paired tissues where the
extent of whole tissue stimulation, as evidenced by transtissue water flow,
was either maximal or submaximal. The results indicate that individual cell
responsiveness within the same tissue to standardized maximal ADH treatment
varies between two- and sevenfold, depending on the morphological endpoint
measured. Furthermore, based on skewness in endpoint distribution, this
variability appears to reflect inherent heterogeneity of granular cell
reactivity to hormone. In relation to proportional tissue responses
elicited by different stimulating concentrations of ADH, our observations
of luminal membrane aggregate incidence suggest that the responding cells,
whatever their sensitivity, participate in a graded, rather than
"all-or-none," "on-off" manner.
