Summary
The effects of acidosis and extracellular calcium were examined at 20°C in the isolated spontaneously contracting atria of the freshwater turtle (Chrysemys picta bellii). The atria were subjected to treatments of lactic acidosis, hypercapnic acidosis or chloride acidosis in the presence of both normal (2.0 mM) and high (10.0 mM) calcium, which simulated levels of acidosis and calcium observed in vivo. In all cases of acidosis, pH was reduced to 6.80 from a control pH of 7.80.
All three forms of acidosis significantly depressed the force of atrial contraction. During lactic and chloride acidosis a progressive decrease in contractile force was seen, while during hypercapnic acidosis a spontaneous partial recovery was observed following an initial sharp drop in tension. Hypercapnic acidosis had the most rapid effect on contractility, while chloride had the slowest effect.
Elevated levels of calcium during lactic and hypercapnic acidoses significantly moderated the negative inotropic effects of acidosis, although contractile force was still below pre-acid values. During chloride acidosis with increased [Ca], no decline in contractile force was observed compared to the control values. Each of the three types of acidoses caused a significant decrease in the frequency of the spontaneous atrial contractions but this effect was not significantly improved with acidosis plus increased [Ca].
Based on the present findings and on related observations of acidosis, it appears that the fresh-water turtle is able to compensate for the negative inotropic effects on the heart of both lactic and hypercapnic acidosis, and these compensations may contribute to its remarkable tolerance to anoxia.
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Yee, H.F., Jackson, D.C. The effects of different types of acidosis and extracellular calcium on the mechanical activity of turtle atria. J Comp Physiol B 154, 385–391 (1984). https://doi.org/10.1007/BF00684445
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DOI: https://doi.org/10.1007/BF00684445