CAMP induces up-regulation of ET A receptor mRNA and increases responsiveness to endothelin-1 of rat aortic smooth muscle cells in primary culture

Abstract

The effects of cAMP on the expression of ET A (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 Ca 2+ concentrations ([Ca 2+] i). Incubation of the smooth muscle cells with 10 μM forskolin and 10 μM 3-isobutyl-1-methyl-xanthine (IBMX) induced an increase in ET A receptor mRNA by 420 % of control after 24 hours. ET-1 induced a biphasic increase in [Ca 2+] i, first transient and second sustained phases. Incubation of the smooth muscle cells with forskolin and IBMX for 24 hours increased the [Ca 2+] 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 ET A receptor mRNA and increases responsiveness to ET-1 of rat aortic smooth muscle cells in primary culture.