Premium
The Effect of Intracellular pH on Myocardial Calcium Sensitivity in the Anoxia‐Tolerant Painted Turtle
Author(s) -
Fanter Cornelia E,
Warren Daniel E,
Campbell Kenneth S
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.760.22
Subject(s) - contractility , calcium , painted turtle , myofilament , intracellular , chemistry , biophysics , calcium in biology , myofibril , myocyte , oxygen , biology , biochemistry , turtle (robot) , endocrinology , ecology , organic chemistry
The anoxia‐tolerant western painted turtle, Chrysemys picta belli, has the ability to survive without oxygen for over 170 days at 3°C due to extreme metabolic responses that minimize energy usage. Under such conditions, the heart minimizes rate and contractility, resulting in a decreased cardiac output. The onset of anoxia is accompanied by a substantial decrease in intracellular pH, which suggests that the reduction in contractility results mostly from mechanical changes in the myofilament sensitivity to Ca2+ associated with intracellular H+ accumulation. To test this hypothesis, the cellular mechanical properties of turtle myocardium were studied at different pH's from turtles exposed to either 24 hours of anoxic or normoxic conditions at 20°C. Multicellular preparations of turtle ventricles were chemically permeabilized and subsequently attached to a motor and force transducer. Preparations were exposed to an array of pCa solutions varying in pH from 7.4 to 6.6 at 22 °C. The concentration of calcium required to trigger 50% of maximum tension (pCa50) decreased stepwise: pCa50 was 6.2, 5.9 and 5.6 for pH's 7.4, 7.0 and 6.6, respectively. The shift in pCa50 indicates that as pH decreases, 50% tension production requires higher calcium levels. Additionally, maximum contractile force decreased as pH decreased. These data indicate that an increased concentration of H+ results in reduced myofilament sensitivity to calcium and, therefore, a decreased ability for force development. Comparisons between normoxic and anoxic tissues indicated no mechanical differences, suggesting that the metabolic changes seen at the onset of anoxia are likely to be a response of intracellular compositional changes of the chemical environment, rather than structural changes to the contractile apparatus. Overall, pCa50 the painted turtle myocardium is intrinsically more sensitive to calcium concentrations (5.9 at pH 7.0) when compared to human and rat (5.67 and 5.2 at pH 7.0), but is similar to other ectotherms. Support or Funding Information This work was supported by a CAREER award from the National Science Foundation.