ABSTRACT
We aimed to determine how increases in intracellular H+ and inorganic phosphate (Pi) to levels observed during anoxic submergence affect contractility in ventricular muscle of the anoxia-tolerant Western painted turtle, Chrysemys picta bellii. Skinned multicellular preparations were exposed to six treatments with physiologically relevant levels of pH (7.4, 7.0, 6.6) and Pi (3 and 8 mmol l−1). Each preparation was tested in a range of calcium concentrations (pCa 9.0–4.5) to determine the pCa–tension relationship for each treatment. Acidosis significantly decreased contractility by decreasing Ca2+ sensitivity (pCa50) and tension development (P<0.001). Increasing [Pi] also decreased contractility by decreasing tension development at every pH level (P<0.001) but, alone, did not affect Ca2+ sensitivity (P=0.689). Simultaneous increases in [H+] and [Pi] interacted to attenuate the decreased tension development and Ca2+ sensitivity (P<0.001), possibly reflecting a decreased sensitivity to Pi when it is present as the dihydrogen phosphate form, which increases as pH decreases. Compared with that of mammals, the ventricle of turtles exhibits higher Ca2+ sensitivity, which is consistent with previous studies of ectothermic vertebrates.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: C.E.F., D.E.W.; Methodology: C.E.F., K.S.C., D.E.W.; Formal analysis: C.E.F., K.S.C.; Investigation: C.E.F., K.S.C., D.E.W.; Writing - original draft: C.E.F., D.E.W.; Writing - review & editing: C.E.F., K.S.C., D.E.W.; Supervision: D.E.W.; Project administration: D.E.W.; Funding acquisition: D.E.W.
Funding
This work was supported by National Science Foundation CAREER grant 1253939 awarded to D.E.W.
Supplementary information
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.164137.supplemental
- Received June 2, 2017.
- Accepted September 17, 2017.
- © 2017. Published by The Company of Biologists Ltd
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