Unmasking of a periodic Na+ entry into glucose-stimulated pancreatic beta-cells after partial inhibition of the Na/K pump

Endocrinology
E Grapengiesser

Abstract

The cytoplasmic concentration of Na+ ([Na+]i) was measured in individual mouse beta-cells using dual wavelength microfluorometry and the indicator sodium-binding benzofuran isophtalate. Under conditions known to induce large amplitude oscillations in cytoplasmic Ca2+ (1.3 mM Ca2+; 11 mM glucose), [Na+]i remained low and stable at 10-14 mM. Partial suppression of the Na/K pump with 50 microM ouabain resulted in oscillations of [Na+]i in 65% of the cells (frequency, 0.13+/-O.O1 min(-l); amplitude, 4.4 +/-0.3 mM). The oscillations were unaffected by the presence of 3 microM tetrodotoxin, but disappeared when the medium was depleted of Ca2+ or supplemented with 10 microM methoxyverapamil. The analysis of the ouabain effect was facilitated by replacing extracellular Ca2+ with 5 mM Sr2+. In the Sr2+-containing medium, oscillations of [Na+]i were seen in more than 70% of the beta-cells exposed to 11 mM glucose. Ouabain (50 microM) modified the [Na+]i oscillations by increasing their amplitudes almost 3-fold and reducing the frequency from once every 3 min to once every 10 min. A relationship between oscillations of cytoplasmic Sr2+ and Na+ was apparent both from observations of similar frequencies and for the modifications obtained wi...Continue Reading

Citations

Jun 29, 2011·The Journal of General Physiology·Chae Young ChaAkinori Noma
Jul 16, 2010·American Journal of Physiology. Endocrinology and Metabolism·L E FridlyandL H Philipson
Dec 13, 2006·Biochemical and Biophysical Research Communications·Susanne UllrichFlorian Lang
Apr 11, 2014·FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology·Iulia I NitaIsrael Sekler
Mar 20, 2003·American Journal of Physiology. Endocrinology and Metabolism·Leonid E FridlyandLouis H Philipson
Oct 10, 2003·American Journal of Physiology. Endocrinology and Metabolism·Yoshikazu Miura, Hisao Matsui
Feb 23, 2020·Seminars in Cell & Developmental Biology·Olof Idevall-Hagren, Anders Tengholm

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