[The effects of prostaglandin I2 on membrane Na+, K+ transport systems in cultured vascular smooth muscle cells].

To investigate the effects of prostaglandin I2 (PGI2) on cation regulation in vascular smooth muscle cells (VSMC), cAMP production, cytosolic free calcium concentration and cellular membrane Na+, K+ transporter activities were measured in the presence or absence of PGI2. The results were as follows. 1. PGI2 (10(-7) M) increased cAMP production, but had no effect on the cytosolic free calcium concentration of cultured VSMC. 2. PGI2 (10(-7), 10(-6) M) had no effect on ouabain-sensitive 86Rb uptake (Na+ -K+ pump activity) of cultured VSMC, but at a higher concentration (10(-5) M), PGI2 inhibited ouabain-sensitive 86Rb uptake. 3. PGI2 (10(-5) M) also inhibited 5-N, N hexamethylene amiloride (HMA)-sensitive 22Na uptake (Na+ -H+ antitransporter activity) of cultured VSMC in the presence of ouabain. 4. PGI2 (10(-5) M) had no effect on bumetanide-sensitive 86Rb washout (Na+ -K+ cotransporter activity) of cultured VSMC. These results suggest the possibility that PGI2 has a biphasic effect: PGI2 elicits relaxation at lower concentrations, but contraction at higher concentrations in cultured VSMC.