AJP - Cell Physiology, Vol 259, Issue 5 C762-C768, Copyright © 1990 by American Physiological Society
Pb2(+)-induced secretion from bovine chromaffin cells: fura-2 as a probe for Pb2+
J. L. Tomsig and J. B. Suszkiw
Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, Ohio 45267-0576.
The effect of Pb2+ on catecholamine release was studied in isolated intact
and permeabilized bovine chromaffin cells. Fura-2 was used to monitor
intracellular Pb2+. A characterization of Pb2(+)-fura-2 interactions in
solutions simulating intracellular ionic composition showed that Pb2+ forms
a 1:1 Pb2(+)-fura-2 complex (apparent dissociation constant = 4.2 x 10(-12)
M, pH 7.05) whose fluorescence resembles that of the Ca2(+)-fura-2 complex.
Spectra recorded from fura-2-loaded cells indicate entry of Pb2+ into the
cells. Intracellular Pb2+ concentrations were proportional to extracellular
Pb2+ concentrations and were found to be 10(-11)-10(-12) M in cells exposed
to micromolar Pb2+ concentrations. Pb2+ elicited the release of tritiated
norepinephrine from fura-2-loaded cells, indicating the extraordinary
effectiveness of Pb2+ as a releasing agent. Permeabilization of cells with
digitonin showed that Pb2+ is able, in the absence of Ca2+, to produce
exocytotic release at concentrations of 3.2 x 10(-10) M or higher (3 orders
of magnitude lower than Ca2+). These results support the notion that Pb2+
can act as a potent Ca2+ surrogate in triggering secretion.
