Relationship between the shape and the membrane potential of human red blood cells |
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Authors: | Ellen M Bifano Terri S Novak Jeffrey C Freedman |
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Institution: | (1) Departments of Pediatrics and Physiology, State University of New York, Upstate Medical Center, 13210 Syracuse, New York |
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Abstract: | Summary Microscopic observations of isotonic suspensions of human red blood cells demonstrate that cell shape is unaltered when the transmembrane electrical potential, orE
m
, is set in the range –85 to +10 mV with valinomycin at varied external K+, or K
o
.E
m
was measured with the fluorescent potentiometric indicator, diS-C3(5), as calibrated by a pH method. Repeating Glaser's experiments in which echinocytosis was attributed to hyperpolarization, we found that at low ionic strength the pH-dependent effects of amphotericin B appear to be unrelated toE
m
. The effects of increased intracellular Ca2+, or Ca
o
, on echinocytosis and onE
m
are separable. With Ca ionophore A23187 half-maximal echinocytosis occurs at greater Ca
o
than that which induces the half-maximal hyperpolarization associated with Ca-induced K+ conductance (Gardos effect). Thus, cells hyperpolarized by increased Ca
o
remain discoidal when Ca is below the threshold for echinocytosis. With A23187 and higher Ca
o
, extensive echinocytosis occurs in cells which are either hyperpolarized or at their resting potential. The Ca-activation curve for echinocytosis is left-shifted by low K
o
, a new observation consistent with increased DIDS-sensitive uptake of45Ca by hyperpolarized cells. These results support the following conclusions: (1) the shape and membrane potential of human red blood cells are independent under the conditions studied; (2) in cells treated with A23187, the Gardos effect facilitates echinocytosis by increasing Ca. |
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Keywords: | red blood cells membrane potential calcium Ca ionophore A23187 fluorescence cell shape |
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