Potassium ion enhances tissue-type plasminogen activator expression in cultured HEL cells

Abstract

The effects of inorganic cations on the production of t-PA in cultured human embryonic lung (HEL) cells were studied. Adding K + or Ca 2+ to the cultured medium for HEL cells increased t-PA release into the medium in a dose-dependent manner. To investigate the intracellular response caused by increment of extracellular K + concentration, intracellular Ca 2+ concentration and intracellular pH were measured. Increasing extracellular K + caused an increase in intracellular pH, but did not affect intracellular Ca 2+ levels. It was also found that extracellular Ca 2+ increased the level of t-PA mRNA by northern blot analysis using human t-PA cDNA fragment as a probe, while extracellular K + did not. When the extracellular pH was decreased from 7.4 to 6.6, intracellular pH detected using the BCECF method was found to have shifted to a higher pH than the extracellular pH. Furthermore, the maximum production of t-PA was obtained at a pH range in which the difference between intracellular pH and extracellular pH was the greatest. Maximum t-PA release was observed at a K + of about 32.2 mM in dishes. A similar effect of K + on t-PA release was also observed in 10 l spinner flasks. Furthermore, the addition of K + to the cultured medium markedly increased the specific glucose consumption rate. It is concluded that K + seems to affect t-PA production at the post-transcriptional level through changes in intracellular pH and glucose consumption.