Pressure-Induced Changes in Intracellular pH Facilitate the Myogenic Response of Rat Small Tail Arteries

The myogenic response contributes considerably to blood flow autoregulation. Intracellular pH (pH_i) has a substantial impact on small artery contractility. However, the role of putative pH_i changes during myogenic constriction is unknown. Therefore, the hypothesis was tested that changes in pH_i are associated with and contribute to the myogenic response in small arteries.

Rat small tail arteries were studied using isobaric myography and BCECF- as well as FURA-2-fluorimetry.

We found that in response to a pressure increase, pH_i decreased. It initially reached a peak and then recovered partly. The initial pH_i peak is augmented in bicarbonate-free solution, but was not affected by inhibitors of Na⁺/H⁺ exchange. The pH_i recovery was not altered in bicarbonate-free solution, but was reduced by inhibitors of Na⁺/H⁺ exchange. Proton fluxes were larger at 80 mmHg than at 10 mmHg. Bicarbonate-free solution had no effect on proton fluxes at either 80 mmHg or 10 mmHg. Inhibitors of Na⁺/H⁺ exchange reduced proton fluxes only at 80 mmHg. Pressure-induced changes in intracellular calcium were not affected by either bicarbonate-free solution or inhibitors of Na⁺/H⁺ exchange.

This study showed that in rat small tail arteries a pressure increase is accompanied by a decrease in pH_i that appears to facilitate the myogenic response. The results of this study suggest that the pressure-induced immediate fall in pH_i is caused by a release of protons from the contractile machinery, and that the subsequent pH_i recovery is due to activation of Na⁺/H⁺ exchange.