cAMP induces up-regulation of ETA receptor mRNA and increases responsiveness to endothelin-1 of rat aortic smooth muscle cells in primary culture.

The effects of cAMP on the expression of ETA (ET-1 selective type) receptor mRNA and on the response to endothelin-1 (ET-1) were investigated in rat aortic smooth muscle cells in primary culture, using reverse transcription polymerase chain reaction (RT-PCR) and fura-2 microfluorometry of cytosolic Ca2+ concentrations ([Ca2+]i). Incubation of the smooth muscle cells with 10 microM forskolin and 10 microM 3-isobutyl-1-methyl-xanthine (IBMX) induced an increase in ETA receptor mRNA by 420% of control after 24 hours. ET-1 induced a biphasic increase in [Ca2+]i, first transient and second sustained phases. Incubation of the smooth muscle cells with forskolin and IBMX for 24 hours increased the [Ca2+]i response by 849% in the first phase and 286% in the second phase, compared with time-matched controls. From these results, we conclude that cAMP induces an up-regulation of the ETA receptor mRNA and increases responsiveness to ET-1 of rat aortic smooth muscle cells in primary culture.