Chadapust Sudsiri - Department of Industrial Management, Faculty of Sciences and Industrial Technology Prince of Songkla University – Suratthani, 84000 Thailand
Raymond Jame Ritchie - Biotechnology of Electromechanics Research Unit, Faculty of Technology and Environment, Prince of Songkla University – Phuket, 83120 Thailand
The electrical conductivity (σ in units of S m-1) of an electrolyte is determined by the concentration and mobility of its ions. Therefore, the electrical conductivity of the cell interior should provide information about the state of the ions within the cell, i.e., whether or not they are free moving or bound by ion exchanger mechanisms to components of the cytoplasm such as proteins. It is a key measurement for dielectric studies on cells. One of the most thoroughly investigated cells is the red blood cell of mammals. This cell exhibits a simple architecture, and its composition of proteins and lipids is well known. Pauly and Schwan, (1966) measured the internal conductivity of erythrocytes and found a value of 0.518 S m-1 at 25 oC (σ25 = 0.518 S m- 1). They concluded that the internal conductivity is largely due to the inorganic ionic content composed primarily of K+, Na+, Mg++, Cl-, and HCO3 - whose concentrations are relatively easy to measure experimentally. The concentration of ions of haemoglobin due to their net charge was reported to be +45 mmol charge/l (cell H2O) from a total concentration of haemoglobin of 7 mM (cell H2O) and so the mean effective +ve charge per haemoglobin molecule was +6.4 (Pauly and Schwan, 1966). The calculation of cytoplasmic conductivity from the ionic concentration of ions present in the cytoplasm multiplied by their limiting ionic conductance according to Kohlrausch’s law gave a value of σ = 1.45 S m-1 which is 2.7 times higher than that obtained from experimental measurements by Pauly and Schwan, (1966) (σ25 = 0.518 S m-1). They concluded that the discrepancy between ideal specific conductivity and the measured value was due to the ionic mobility being hindered by cytoplasmic viscosity (Pauly and Schwan, 1966). However, since most mammalian cells regulate their volumes, after the initial passive swelling (stomatocytogenic) or shrinking (echinocytogenic) as a result of changes in the bathing electrolyte and/or temperature, cells usually return to a near-normal volume (Glaser, 1979). Red blood cells quickly change their cell volumes because water moves quickly into them through water channel proteins called aquaporins which do not allow charged ions to pass through them (Murata et al., 2000). Several mechanisms are involved in the slower process of adjusting their cell volume back to normal, in most cases involving the loss and gain of K+ and Cl- and to a lesser extent Na+(Glaser, 1979; Bernhardt, 1991; Parker, 1993; O’Neill, 1999). A perturbation of cell volume will certainly disturb the concentration of ions present in the cytoplasm as described by Glaser and Donath, (1984) and consequently cause the cytoplasmic conductivity to shift from the normal physiological state. In this investigation, the cytoplasmic conductivity of human red blood cells (HRBCs) at different temperatures was observed. The cell volumes and cell water contents in the cells were measured experimentally. The cytoplasmic conductivity (σc ) was calculated according to the Debye - Hückel – Onsager equation combined with Walden’s rule (Laidler and Meiser, 1995) and its temperature coefficient was then estimated.
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