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Relationship between the shape and the membrane potential of human red blood cells
Authors:Ellen M Bifano  Terri S Novak  Jeffrey C Freedman
Institution:(1) Departments of Pediatrics and Physiology, State University of New York, Upstate Medical Center, 13210 Syracuse, New York
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 DeltapH 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.
Keywords:red blood cells  membrane potential  calcium  Ca ionophore A23187  fluorescence  cell shape
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