Angiotensin II-induced calcium signalling in isolated glomeruli from fish kidney (Oncorhynchus mykiss) and effects of losartan

Glomeruli were isolated from the kidney of freshwater-adapted rainbow trout , Oncorhynchus mykiss, to qualitatively evaluate changes in cellular calciu m associated with angiotensin II ([Asn(1)Val(5)]-Ang II) receptor stimulati on and antagonism by the Ang II receptor antagonist losartan. Microspectrof luorometry using the fluorescent calcium indicator dye Calcium Green record ed fluorescence changes in isolated single glomeruli. Isolated glomeruli co ntaining ester-loaded Calcium Green showed an Aug-II-induced transient rise in fluorescence. This transient rise showed an increased peak amplitude wi th increased Ang II concentration (10(-9) to 10(-6) M), but only a very sma ll response was detectable in glomeruli exposed to 10(-9) M Ang II. The bip henylimidazole compound losartan (= DuP 753), an antagonist of the mammalia n AT(1) subtype Ang II receptor, initiated a transient agonistic rise in gl omerular fluorescence at high concentration (10(-5), 10(-4), and 10(-3) M). However, the responses to 10(-6) 10(-7) M losartan were small or very low in each case. Losartan (10(-4) or 10(-7) M) antagonised the Ang-II-induced signalling in isolated glomeruli exposed to 10(-7) or 10(-6) M Ang II, resp ectively. This is the first evidence for functional AT(1)-like Ang II recep tors coupled to cellular calcium signalling in the glomeruli of rainbow tro ut. (C) 1999 Academic Press.