Contributions of [Ca2+]i, [Pi]i, and pHi to altered diastolic myocyte tone during partial metabolic inhibition.

Abstract

Ischemia may cause increased or decreased distensibility of the left ventricle, but the cellular mechanisms involved have not been clarified. We examined the possible contributions of changes in intracellular inorganic phosphate, pH, and Ca2" concentrations to altered diastolic function in cultured myocytes subjected to partial metabolic inhibition. Paced cultured embryonic chick and adult rabbit ventricular myocytes superfused with 20 mM 2-deoxyglucose (2DG) exhibited an increase in end-diastolic intracellular free calcium concentration ([Ca2`J,) and an upward shift in end-diastolic cell position.These results indicate that glycolytic blockade increases diastolic and systolic calcium in paced ventricular myocytes, and that this elevated diastolic calcium influences the extent of diastolic relaxation. In contrast, paced ventricular myocytes superfused with 1 mM cyanide (CN) exhibited a similar increase in end-diastolic [Ca2"ji but a decrease in end-diastolic cell position and amplitude of motion. Although changes in ATP contents were similar in both groups (2DG, -29.9%; CN, -40.1%), alterations of intracellular pH and inorganic phosphate concentrations were different. In 2DG-treated cells, pHi did not decrease significantly (7.18±0.04 to 7.12±0.11, n = 14) but in the CN group it decreased markedly within 6 min (7.18±0.04 to 6.76±0.11, n = 11, P < 0.01). Intracellular inorganic phosphate decreased slightly in the 2DG group (-14.8%, NS) but increased in cells exposed to CN (45.7%, P < 0.02). We conclude that while a prominent increase in diastolic [Ca2+J occurs in rapidly paced ventricular myocytes exposed to either inhibitors of glycolysis or oxidative phosphorylation, the effects of this increase in [Ca2"1 on diastolic distensibility may be influenced by intracellular accumulation of metabolites that decrease the sensitivity of myofilament to [Ca2"J. (J. Clin. Invest.

Glycolytic inhibition: effects on diastolic relaxation and intracellular calcium handling in hypertrophied rat ventricular myocytes.

“…To assure that the results obtained in isolated myocytes were representative of the behavior of the intact heart, the 2DG perfusion protocol described above in the isolated myocytes were repeated in isolated buffer-perfused hearts from additional aortic-banded rats 8-9 wk after banding (n = 7) and age-matched sham-operated controls (n = 7). The isovolumic buffer-perfused heart preparation has been described in detail previously (11,12,13). Left ventricular isovolumic balloon volume was adjusted to achieve a left ventricular end-diastolic pressure of 10 mmHg in both groups; at this level of diastolic pressure, balloon volume was comparable in the hypertrophy and control groups (0.19±0.01 vs. 0.21±0.02 ml, NS).…”

“…There is evidence that glycolytic flux is closely linked with diastolic relaxation and transsarcolemmal ion flux, implicating a role in the restoration of resting cytosolic Ca2" levels (9, 10). Ikenouchi et al ( 11 ) demonstrated that glycolytic inhibition by 2-deoxyglucose (2DG) 1 causes impairment of myocyte relaxation in association with an increase in diastolic intracellular Ca2" in normal isolated cultured embryonic chick myocytes and paced adult rabbit ventricular myocytes under oxygenated conditions.…”

“…Continuous retrograde coronary perfusion was initiated at a perfusion pressure of 70 cm H20 for control hearts and 100 cm H2O for hypertrophied hearts. The heart was first perfused with nominally Ca2+-free modified Krebs (11). First, 10 ml of fetal bovine serum was mixed with 234 k1 of 25% Pluronic F 127 (BASF Wyandotte Corp., Parsippany, NJ) dissolved in dimethyl-sulfoxide.…”

“…The coverslip was rinsed with indo-l AM-free buffer solution, and placed in a flowthrough heated (36°C) cell superfusion chamber on the stage of an inverted microscope (Nikon, Tokyo, Japan). The instrumentation for fluorescence measurement has been described in detail elsewhere (11,18,19). The excitation source was a high-pressure Hg-arc lamp which provides an intense emission peak at 360 NM.…”

Mechanism of the diastolic dysfunction induced by glycolytic inhibition. Does adenosine triphosphate derived from glycolysis play a favored role in cellular Ca2+ homeostasis in ferret myocardium?

“…Such beneficial effects of glycolysis have been attributed to a preferential ability of glycolytically derived ATP to restore calcium homeostasis (20). Other lines ofevidence have also hinted at linkages between glycolytic inhibition and abnormal Ca2" homeostasis (21)(22)(23).…”