Linked oscillations of free Ca2+ and the ATP/ADP ratio in permeabilized RINm5F insulinoma cells supplemented with a glycolyzing cell-free muscle extract.

B E Corkey,K Tornheim,J T Deeney,M C Glennon,J C Parker,F M Matschinsky,N B Ruderman,M Prentki

doi:10.1016/s0021-9258(18)68917-3

Abstract

We show in the accompanying paper that the steady-state level of free Ca2+ maintained by the organelles of permeabilized RINm5F insulinoma cells varies inversely with the ATP/ADP ratio when this ratio is set by addition of creatine phosphokinase and fixed ratios of creatine to creatine phosphate. We, therefore, asked whether acute cyclic alterations in the cytosolic ATP/ADP ratio in the range known to modulate O2 consumption might be involved in regulating the physiological activity of Ca2+ -ATPases and the cytosolic free Ca2+ level. To explore this hypothesis we combined two experimental systems: 1) permeabilized RINm5F insulinoma cells that can maintain a low medium Ca2+ concentration and 2) a cell-free extract of rat skeletal muscle that spontaneously exhibits oscillatory behavior of glycolysis and linked oscillations in the ATP/ADP ratio, when provided with glucose. The free Ca2+ level maintained by the permeabilized cells oscillated in phase with the glycolytic oscillations and correlated closely with the ATP/ADP ratio but not with glucose 6-phosphate, fructose 6-phosphate, orthophosphate, or pH. When glucokinase replaced hexokinase as the glucose phosphorylating enzyme, Ca2+ oscillations were induced by increasing the glucose concentration from 2 to 8 mM. The results demonstrate a link between metabolite changes and free Ca2+ levels in a reconstituted physiological system. They support a model in which oscillations in glycolysis and the ATP/ADP ratio may cause oscillations in cytosolic free Ca2+, beta-cell electrical activity, and insulin release.

Highlights

We show in theaccompanying paper that the steady- is buffered at fixed values by thecreatinephosphokinase state level of free Ca2+ maintainedby the organellesof equilibrium [13]
Whenglucokinase rather than hexokinase was employed as theglucose phosphorylating enzyme, this behavior was dependent on theglucose concentration.Theresults lead us to hypothesize that metabolic oscillations could underlie the observed oscillations in @-cell membrane potential and insulin secretion [1,2,3,4,5,6]
Ca2+ concentration in this experimeonstcillated between 180 respect, it insoteworthy that controlof respiration inisolated and 230 nM, levels in the range reported to stimulate insulin rat liver mitochondria is observed between ATP/ADP ratios release from permeabilized islets [31, 32].Similar oscillations of 5 and 100 at constantlevels of orthophosphate [36]

Summary

Introduction

We show in theaccompanying paper that the steady- is buffered at fixed values by thecreatinephosphokinase state level of free Ca2+ maintainedby the organellesof equilibrium [13]. The frequency and amplitude of the oscillations are sulinoma cells that can maintain a low medium Ca2+ dependent on the rate of glucose phosphorylation and net concentration and2) a cell-free extractof rat skeletal ATPase activity as well as the levels of allosteric regulators muscle that spontaneously exhibits oscillatory behav- of phosphofructokinase [17].

Results

Conclusion