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Dual effects of Na/K pump inhibition on cytoplasmic Ca2+ oscillations in pancreatic beta-cells
E Grapengiesser1, A Berts, S Saha
1Department of Medical Cell Biology, Uppsala University, Sweden.
Abstract:
Inhibition of the Na/K pump by ouabain or removal of K+ resulted in gradual increase of intracellular sodium in beta-cell-rich pancreatic islets from ob/ob-mice exposed to 3 mM glucose. In individual beta-cells this action of ouabain was paralleled by closure of ATP-regulated K+ channels and a slow elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i). In most beta-cells an increase of the glucose concentration to 11-20 mM induced large amplitude oscillations of [Ca2+]i with a frequency of 0.2-0.5/min. Ouabain had dual actions on these glucose-induced oscillations in promoting their appearance and at higher concentrations transforming them into a sustained increase of [Ca2+]i. At 100 microM ouabain reduced the frequency of the glucose-induced oscillations but nevertheless raised the time-average [Ca2+]i by increasing the amplitudes and half-widths of the Ca2+ peaks. When high concentrations of ouabain or removal of K+ transformed the oscillations into a sustained increase of [Ca2+]i, the level reached exceeded that obtained in response to rise of glucose alone. By favoring Ca2+ entry and counteracting removal of the cation from the cytoplasm, Na/K pump inhibition perturbs the balance between the processes determining glucose-induced oscillations of [Ca2+]i.
Insights
Inhibiting the sodium-potassium pump in pancreatic beta cells disrupts intracellular sodium and calcium levels. This affects glucose-stimulated calcium oscillations crucial for insulin secretion.
Area of Science:
- Cellular physiology
- Endocrinology
- Metabolic research
Background:
- Pancreatic beta cells regulate glucose homeostasis through insulin secretion.
- Glucose stimulates insulin release by increasing intracellular calcium concentration ([Ca2+]i).
- The sodium-potassium (Na/K) pump plays a role in maintaining ion gradients within beta cells.
Purpose of the Study:
- To investigate the effect of Na/K pump inhibition on intracellular sodium and [Ca2+]i in pancreatic beta cells.
- To determine how Na/K pump inhibition influences glucose-induced calcium oscillations.
- To elucidate the role of the Na/K pump in regulating beta cell function.
Main Methods:
- Using beta-cell-rich pancreatic islets from ob/ob-mice.
- Inhibiting the Na/K pump with ouabain or removing extracellular potassium (K+).
- Measuring intracellular sodium and [Ca2+]i under varying glucose concentrations.
Main Results:
- Na/K pump inhibition increased intracellular sodium and elevated [Ca2+]i.
- Ouabain promoted the appearance of glucose-induced [Ca2+]i oscillations and, at higher concentrations, caused sustained [Ca2+]i increases.
- Na/K pump inhibition altered the frequency, amplitude, and duration of glucose-induced calcium oscillations.
Conclusions:
- Na/K pump inhibition perturbs the balance of ion transport in beta cells.
- This perturbation affects glucose-induced calcium oscillations, impacting beta cell function.
- The Na/K pump is critical for maintaining the normal oscillatory pattern of [Ca2+]i in response to glucose.