Functional expression of angiotensin II receptors in type-I cells of the rat carotid body

Angiotensin II increases afferent discharge from the carotid body in vitro. We hypothesized that angiotensin II receptors (AT receptors) are expressed functionally in the type-I cell of the carotid body. Cytosolic free [Ca2+] ([Ca2+](i)) in type-I cells freshly dissociated from rat carotid bodies wa s measured spectrofluorimetrically. Angiotensin II (10-100 nM) concentratio n-dependently increased [Ca2+](i) in type-I cells. The [Ca2+](i) response w as blocked by pretreatment with losartan (1 muM), an AT(1) receptor antagon ist, but not by blockade of AT(2) receptors with PD-123319 (1 muM). Moreove r, the gene expression of AT(1) receptors was assessed by the reverse trans criptase polymerase chain reaction and gene transcripts of both AT(1a) and AT(1b) receptors were detected in the carotid body. In addition, immunohist ochemical study revealed that AT(1) immunoreactivity was localized in lobul es of type-I cells in the carotid body. Taken together, these results sugge st that type-I cells in the rat carotid body express functional angiotensin II receptors. The binding of angiotensin II to the AT(1) receptors increas es [Ca2+](i), a key step of the intracellular signalling cascade following the activation of the receptors. It is concluded that angiotensin II modula tes carotid body chemoreceptor function directly via AT(1) receptors in the type-I cell.