[Effect of changes in pH on intracellular Ca2+ and cell length of myocytes]

To examine the effects of pHi on [Ca2+]i, cell length and Ca2+ sensitivity of myofilaments in rat myocyte.

We used microscopic spectral imaging approach to monitor simultaneously [Ca2+]i, pHi and cell length with fluorescent indicator indo-1 and SNARF-1 in isolated single rat myocyte.

Exposure of cell to 20 mmol/L Sodium Propionate induced an intracellular acidosis which increased slightly systolic and diastolic [Ca2+]i, decreased the cell shortening (CS) and Ca2+ sensitivity of myofilament (P < 0.01). Exposure of cell to 15 mmol/L NH4Cl induced an intracellular alkalosis which decreased systolic and diastolic [Ca2+]i, increased the cell shortening and Ca2+ sensitivity of myofilament (P < 0.01).

In the early time of acidosis, [Ca2+]i, as well as cell length increases respectively. While alkalosis, [Ca2+]i and cell length decreases respectively. The effect of acidosis and alkalosis on Ca2+ sensitivity presents non-linear relationship, i.e. the effect of acidosis on sensitivity, caused by pHi change, is less than that of alkalosis.