Cardiac pH Regulation and Buffering of the Western Painted Turtle ( Chrysemys picta belli )

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The western painted turtle (Chrysemys picta bellii) spends its winters below the ice where oxygen sources are depleted, during which they rely on anaerobic metabolism. During this anoxia, the heart accumulates the highest lactates and has the lowest intracellular pH of any organ, while cardiac function, itself, is depressed. To determine whether the buffering power of the painted turtle ventricle is unique from other vertebrates, we used fluorescence microscopy and ammonium chloride pre-pulsing to measure the pH-dependence of total and intrinsic buffering power in isolated ventricular myocytes. Our data show that painted turtle ventricular myocyte intrinsic buffering is lowest (9-2 mequiv L-1) at the pH ranges that occur during anoxia (pH 7.2-6.55) and is highest (62 mequiv L-1) at normal and alkaline pH's (greater than 7.2), which differs from mammals, where the opposite is observed. The same trend is seen with bicarbonate-dependent buffering, where buffering power drops from 44 mequiv L-1 at pH 7.2 to 2 mequiv L-1 at pH 6.8. A decrease in bicarbonate-dependent buffering with decreased pH has been shown in mammals, but is substantially lower in turtles. This leads to a total buffering of between 53 mequiv L-1 and 4 mequiv L-1 during anoxia. We suggest that a decrease in buffering power at a low pH could be an advantage for the turtle, as H+ are allowed to accumulate more quickly, which will have the effect of preventing cross-bridge cycling and preserving ATP. This study was funded by the National Science Foundation.