AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 3 652-R658, Copyright © 1991 by American Physiological Society
Intracellular pH regulation in trout urinary bladder epithelium: Na(+)-H+(NH4+) exchange
W. S. Marshall and S. E. Bryson
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, Canada.
We measured intracellular pH (pHi) of single epithelial cells in situ in
the urinary bladder epithelium using microspectrofluorometry and the
cytoplasmically trapped pH-sensitive fluorophore,
2',7'-bis(2-carboxyethyl)-5(6)- carboxyfluorescein (BCECF). The resting pHi
was 7.21 +/- 0.03 (n = 40 bladders, 489 cells) in pH 7.8 bathing solutions,
indicating that H+ is not passively distributed across the plasma membrane
and is extruded against its electrochemical gradient. Whereas exposure to
hypercapnia (5% CO2 saturation) reversibly decreased pHi, mucosally added
20 mM NH4+ reversibly increased pHi. Recovery from the NH4+ effect was slow
and lacked an acid-load pHi undershoot; this is interpreted as suggesting
significant NH4+ permeability. Recovery from hypercapnic acidosis was
blocked by mucosally added amiloride, indicating that apical Na(+)-H+
exchange is involved in pHi regulation. Addition of 0.5 mM NH4+ to the
basolateral side when the mucosal side was bathed in mock urine (2 mM NaCl)
significantly increased undirectional mucosal-to-serosal Na+ flux, and the
increase was blocked by mucosally added amiloride. We conclude that an
apically located Na(+)-H+ exchange is important in pHi regulation and may
also accept NH4+ as the counterion for Na+.
