Seasonal variations in the fine structure of the Necturus maculosus urinary bladder epithelium: Low transporters and high transporters

Abstract

Although the urinary bladder of Necturus maculosus provides an important model system for studying the mechanisms of active Na absorption, little critical attention has been paid to the fine structure of its epithelium. Moreover, two distinct groups of urinary bladders, low and high Na transporters, have been described based on short-circuit current or transepithelial potential difference. In the present study, over an 11-month period, stable electrical parameters (short-circuit current, transepithelial potential difference, and resistance) were recorded from 63 chamber-mounted bladders. Analysis of these parameters revealed a highly significant difference between two groups (low transporters and high transporters) occurring at different times of the year. Consistent with these data, in urine collected from the bladders, the Na concentration in low transporters was significantly higher than that in high transporters. A subpopulation of these bladders was subsequently fixed and examined at the light and/or electron microscopic level. Low-transporting bladders were characterized unequivocally by a thin, stratified squamous epithelium only 6-15 micron thick. High-transporting bladders were composed predominantly of columnar-shaped granular cells up to 70 micron in height, with ciliated, mitochondria-rich, and basal cells present in small numbers. There is thus a correlation between transport activity, as measured by electrophysiological techniques and urine sodium analysis, and the structure of the tissue. Moreover, these parameters exhibit significant seasonal variation, the underlying mechanisms of which remain obscure.

Characterization of the basolateral membrane conductance of Necturus urinary bladder.

“…A few experiments were conducted on short-circuited bladders . The intracel-' This is consistent with the absence ofnet H+ secretion, in agreement with the rare occurrence of mitochondria-rich cells in this preparation (Karnaky et al, 1984) . lular potential of these bladders (means of 20 impalements performed on four bladders) was -43.5 ± 2.7 mV before and -67.6 ± 3.0 mV after amiloride.…”

Time-dependent phenomena in voltage-clamped epithelia

“…Garcia-Diaz and Essig, it is quite likely that C 9 ~> C '~ so that f(0) ~ t. Morphometric studies of Necturus urinary bladder (Schultz et al, 1984a;Karnaky et al, 1984) are consistent with f(0) ~ 0.97. The suggestion that phase II reflected the response times of the micropipettes appears entirely plausible.…”

Distribution of ion channels on taste cells and its relationship to chemosensory transduction

“…The seasonal variation of the TEA-sensitive channels on the basolateral membrane was unexpected but not unprecedented. For example, the urinary bladder of Necturus also exhibits seasonal variations (Karnaky et al, 1984;Demarest & Finn, 1987a).…”