AJP - Cell Physiology, Vol 253, Issue 2 C309-C315, Copyright © 1987 by American Physiological Society
Measurement of intracellular Ca2+ activity in Necturus gallbladder
C. E. Palant and I. Kurtz
To clarify the effects of Ca2+-free solutions on the electrophysiological
properties of leaky epithelia, Necturus gallbladder was mounted in an
Ussing-type chamber and its mucosal surface exposed to Ca2+-free EGTA (2
mM) Ringer. Lateral-space width was controlled by a -3-cmH2O pressure
gradient on the serosal outflow. Transepithelial potential difference and
resistance were monitored while cell membrane potential and intracellular
Ca2+ activity (Ca2+i) were determined with conventional and Ca2+-sensitive
microelectrodes. Ca2+i averaged 183 +/- 27 nM (n = 15). Reduction of
mucosal Ca2+ activity to approximately 500 nM reversibly lowered
transepithelial resistance while cell membrane potential remained unaltered
and fractional membrane resistance increased from 0.77 +/- 0.01 to 0.83 +/-
0.02 (P less than 0.01, n = 5). In five gallbladders mucosal Ca2+ reduction
induced a significant drop in Ca2+i from 133 +/- 26 to 77 +/- 20 nM (P less
than 0.01, n = 5) while transepithelial resistance fell from 125 +/- 27 to
107 +/- 24 omega X cm2 (P less than 0.01). These results indicate that
transepithelial resistance decrements observed during exposure to Ca2+-free
solutions stem from a reversible increase in tight-junctional but not cell
membrane permeability and that this effect is associated with a fall in
intracellular Ca2+ activity.
