Rat proximal tubule cell line transformed with origin-defective SV40 DNA: autocrine ANG II feedback

The renal proximal tubule (PT) is a major site for a complete demonstrate p ositive ANG II feedback with angiotensinogen tissue renin-angiotensin syste m (RAS) and produces endogenous angiotensin II (ANG II). The present studie s demonstrate autocrine RAS feedback in a line of origin-defective SV40 pla smid transformed immortalized rat PT cells (IRPTC) designated as line 93-p- 2-1, which are highly differentiated and express all RAS components. Recept or competition assays and Southern blot following RT-PCR demonstrated that these IRPTC express AT(1) and AT(2) angiotensin receptor subtypes. Autocrin e RAS feedback was examined following exposure to ANG II (10(-8) M), and it was noted that angiotensinogen mRNA increases significantly by 1 h and rem ains elevated through 24 h. The AT(1) blocker losartan prevents this increa se. Moreover, ANG II upregulates expression of ANG II receptor mRNA (both A T(1) and AT(2)). Thus the present studies and ANC; II receptors in PTC, sug gesting that the main site of such intrarenal feedback in vivo is within PT . ANG II secreted by line 93-p-2-1 is increased by isoproterenol, suggestin g beta-adrenergic regulation in IRPTC.