CA2-INDUCED INHIBITION OF SODIUM-PUMP - EFFECTS ON ENERGETIC METABOLISM OF MOUSE DIAPHRAGM TISSUE()

Tissues of mouse diaphragms were incubated in Liley solution containin g 2, 4, 6 and 10 mmol/l calcium. When diaphragm tissue was incubated i n 10 mmol/l calcium, an increase of intracellular calcium concentratio n from 314 +/- 28 to 637 +/- 26 nmol/l was estimated by fluorescent Ca 2+ indicator Fura-2/AM. Moreover, incubation of the tissue in 10 mmol/ l Ca2+ led to complete inhibition of electrogenic activity of the sodi um pump, as measured by intracellular microelectrodes in a single musc le cell. This inhibition was fully reversible after 5 min washing with Liley solution containing 2 mmol/l CaCl2. The Ca2+-induced blocking e ffect on electrogenic activity of the sodium pump was accompanied by i nhibition of glucose incorporation into the muscle tissue. Calcium at concentrations of 6 and 10 mmol/l in bath medium significantly inhibit ed both CO2 production and O-2 consumption. A continual decrease of re spiration (CO2/O-2) quotient was observed under increasing concentrati ons of calcium. Moreover, an exponential decrease of ATP tissue levels was observed at increasing concentrations of calcium in the bath medi um. On the other hand, massive acceleration of anaerobic glycolysis in duced by incubation of the tissue in a medium containing high calcium concentration is improbable. This may be deduced from the fact that on ly about an 50% increase of lactate content in muscle tissue was obser ved when diaphragms were incubated for 30 min in medium containing cal cium ions at 6 and 10 mmol/l as compared with the control tissue incub ated for the same time in the medium containing 2 mmol/l CaCl2. In con clusion it could be stressed that increase of Ca2+ concentration in ba th medium induced in diaphragm muscle tissue an elevation of intracell ular Ca2+ concentration accompanied by a depression of sodium pump ele ctrogenic activity and a depression of energy metabolism. These change s may be involved in pathology of muscle tissue during the Ca2+ overlo ad.