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

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

METHODS

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

RESULTS

We found that in response to a pressure increase, pHi decreased. It initially reached a peak and then recovered partly. The initial pHi peak is augmented in bicarbonate-free solution, but was not affected by inhibitors of Na+/H+ exchange. The pHi 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.

CONCLUSIONS

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