MECHANISMS OF HYPERCAPNIA-STIMULATED PG PRODUCTION IN PIGLET CEREBRAL MICROVASCULAR ENDOTHELIAL-CELLS

High CO2 stimulates dilator prostanoid (prostaglandin; PG) synthesis by piglet cerebral microvascular endothelial cells, but the mechanism of stimulation is unclear. We address the hypothesis that intracellular pH (pH(i)) and Ca2+ signaling are involved. When extracellular pH (pH(e)) and PCO2 were constant and pH(i) was rapidly reduced (propionate or nigericin), PG synthesis was stimulated. When pH(e) was lowered by reducing NaHCO3, pH(i) fell slowly, but PG synthesis was not altered. When pH(e) was decreased by increasing PCO2 or returned to 7.4 by increasing NaHCO3, with a constant PCO2 of 100 mmHg, pH(i) dropped quickly and PG synthesis was stimulated. When pH(i) was reduced slowly by changing CO2 slowly, or by stepwise addition of propionate, PG synthesis was increased regardless of pH(e), suggesting that the rapid decline of pH(i) plays a central role in mediating the PG synthesis. Ca2+ signaling is a potential mechanism by which pH(i) increases PG synthesis. However, extracellular Ca2+ removal did not affect PG synthesis induced by propionate or hypercapnia. Furthermore, neither rapid nor slow decreases of pH(i) altered cytosolic free Ca2+ concentration. Therefore, Ca2+ signals do not appear to be involved in the CO2 stimulation of PG synthesis.