Changes in intracellular sodium, potassium, and calcium concentrations in transplanted mouse pancreatic islets

Background. Our previous studies have suggested a chronically low oxygen tension in transplanted pancreatic islets. The present study tested the hypothesis that this may be coupled to changes in intracellular concentrations of crucial ions within the transplanted islet cells and, thus, their function. Methods. X-ray microanalysis was used for studies of native islet cells and islet grafts residing for 1 day or 1 month in nondiabetic or diabetic recipients. Results. Markedly increased sodium concentrations and decreased potassium concentrations were recorded in all transplanted islet cells, irrespective of whether the grafts had been implanted into nondiabetic or diabetic recipients or whether they were investigated 1 day or 1 month after transplantation. The calcium concentration in 1-day-old islet grafts was similar to that in native islet cells, but it decreased markedly between 1 day and 1 month after transplantation. Again this was seen in both nondiabetic and diabetic recipients. Conclusions. Most probably, the disturbances in graft sodium and potassium concentrations reflect ATP depletion and inhibition of the Na/K-ATPase in the plasma membrane as a result of impeded oxygen supply. The decreased calcium concentrations developing over time in the transplanted islet cells might be potentially detrimental, because calcium plays a fundamental role in the control of a variety of cellular functions, including insulin secretion, in beta cells.