Protein kinase C and protein kinase A regulate the expression of angiotensin II receptor mRNA in smooth muscle cells

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Using reverse transcription polymerase chain reaction and fura-2 microfluorometry of intracellular Ca 2+ concentrations, we investigated the effects of angiotensin II and cyclic AMP on the expression of angiotensin II type 1 receptor mRNA and the relationship between angiotensin II receptor mRNA level and physiological responsiveness in rat aortic smooth muscle cells in primary culture. Angiotensin II (1 μM) induced a time- and dose-dependent transient decrease in the level of angiotensin II receptor mRNA. The maximal decrease (50 ± 13% of control) occurred at 6 h, followed by a gradual return to the control level within 24 h. H-7 (30 μM), a relatively specific protein kinase C inhibitor, inhibited decrease in the expression of angiotensin II receptor mRNA induced by 6 h angiotensin II treatment, while 6 h stimulation by 0.3 μM phorbol 12-myristate 13-acetate also induced a decrease (35 ± 8% of control) in the expression of angiotensin II receptor mRNA. An increase in cellular cyclic AMP induced by 10 μM forskolin plus 10 μM 3-isobutyl-1-methyl-xanthine, decreased the angiotensin II receptor mRNA level to 50 ± 13% of the control at 6 h and increased it to 219 ± 39% of the control at 48 h of treatment. Angiotensin II-induced decrease and cyclic AMP-induced increase in the expression of angiotensin II receptor mRNA were accompanied by a reduction and enhancement in [Ca 2+] i transients induced by angiotensin II, respectively. In contrast with angiotensin II receptor mRNA level (102 ± 8% of control), the [Ca 2+] i transients were markedly decreased in angiotensin II plus H-7 treated cells. Although the angiotensin II receptor mRNA level was reduced (50 ± 13% of control), the first phasic elevation of [Ca 2+] i was unchanged (104 ± 14% of control) in 6 h forskolin plus 3-isobutyl-1-methyl-xanthine treated cells. These results suggest that (1) angiotensin II, protein kinase C and protein kinase A regulate the expression of angiotensin II receptor mRNA, and that (2) the increase in receptor mRNA level is accompanied by an increase in physiological responsiveness, while the decrease in receptor mRNA is not always accompanied by a decrease in physiological responsiveness.