Differences in Ca2+ pumping activity between sub-populations of human red cells

Area of Science:

• Cellular Physiology
• Biochemistry
• Gerontology

Background:

• Aging human red blood cells exhibit elevated intracellular free calcium (Ca2+).
• The underlying mechanisms for this age-related increase in Ca2+ are not fully understood.

Purpose of the Study:

• To investigate the mechanisms of Ca2+ homeostasis changes in aging human red blood cells.
• To determine if altered Ca2+ influx or extrusion contributes to increased free Ca2+ in senescent cells.

Main Methods:

• Human red blood cells were separated into light and dense subpopulations using Percoll gradients.
• Ca2+ influx rates and Ca2+ pump kinetics (extrusion capacity) were measured in these subpopulations.
• Experiments were conducted at physiological temperature (37°C) and varying pH (7.0 and 7.4).

Main Results:

• No significant differences in the initial rate of Ca2+ entry were observed between light and dense red blood cell fractions.
• The maximal Ca2+ extrusion rate by the Ca2+ pump was approximately 50% lower in the densest (oldest) cell fraction compared to lighter fractions.
• This reduction in extrusion capacity was observed at both pH 7.0 and pH 7.4.

Conclusions:

• The elevated free Ca2+ concentration in senescent human red blood cells is primarily due to a decreased capacity for Ca2+ extrusion.
• Reduced Ca2+ pump activity contributes significantly to the aging of red blood cells.
• The findings suggest a critical role for impaired Ca2+ efflux in red blood cell senescence.