Summary
The effect of acidosis on the myocardial Ca2+ distribution was examined at 15°C in ventricular strips of the flounder (Platichthys flesus) and at 30°C in atrial strips of the rat (Rattus norvegicus).
Lowering the Ringer pH from 7.6 to 6.9 by increasing its CO2 (flounder 2% to 12%, rat 4% to 14%), resulted in an elevated Ca2+ efflux in resting strips as well as in strips stimulated (12/min) to contraction. A decrease in pH of the Ringer used for the flounder myocardium by a lowering of bicarbonate (30 mM to 5 mM) also resulted in an elevation of the Ca2+ efflux, but the effect was smaller than that produced by an increased CO2.
With 11 mM Ca2+ and 10 mM EGTA added to the Ringer to reduce the amount of45Ca2+ bound to extracellular sites, an increased CO2 with a concomitant drop in Ringer pH resulted in an increased Ca2+ efflux in both myocardia. The Ca2+ efflux was only marginally elevated in the flounder myocardium and unchanged in that of rat when the same drop in Ringer pH was produced with a lowering in bicarbonate.
In a nominally Ca2+-free Ringer with 0.1 mM EGTA the45Ca2+ efflux was stimulated for both myocardia by an increase in CO2.
The flounder myocardium was exposed to high CO2 in a nominally Na+, Ca2+-free Ringer and again the45Ca2+ efflux increased. After a return to Na, Ca and low CO2 in the Ringer, a higher efflux persisted in the strips being subjected to a high CO2 than in the controls.
The Ca2+ uptake rate was about the same at high and low CO2 for both myocardia.
Based on these results the measured increase in Ca efflux following an increase in CO2 or a decrease in bicarbonate probably results from an elevated cytoplasmatic Ca2+ activity. It seems unlikely that an increased uptake rate of Ca2+ or a direct stimulation of Ca2+ transporting mechanisms in the cell membrane are responsible for the change.
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Gesser, H., Poupa, O. Acidosis and Ca2+ distribution in myocardial tissue of flounder and rat. J Comp Physiol B 143, 245–251 (1981). https://doi.org/10.1007/BF00797704
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DOI: https://doi.org/10.1007/BF00797704