ATRIAL-NATRIURETIC-PEPTIDE MODULATES THE EFFECT OF ANGIOTENSIN-II ON THE CONCENTRATION OF FREE CALCIUM IN THE CYTOSOL OF MANDIN-DARBY CANINE KIDNEY-CELLS

The effect of angiotensin II (ANG II) and atrial natriuretic peptide ( ANP) on intracellular free calcium concentration [Ca2+](i) was investi gated in Mandin-Darby canine kidney (MDCK) cells in culture. Changes i n [Ca2+](i) were monitored fluorometrically with the Ca2+-sensitive pr obe fura-2/AM at 37 degrees C using a Perkin-Elmer LS-5 spectrofluorim eter (excitation 340/380 nm, slit 3 nm; emission 520 nm, slit 10 nm). MDCK cells exhibited a mean baseline [Ca2+](i) of 98 +/- 10 nM. The ad dition of increasing concentrations of ANG II (1 pM to 1 mu M) to the cell suspension led to a progressive increase in [Ca2+](i) to 2-3 time s basal levels. In contrast, addition of 1 mu M ANP to the cell suspen sion led to a very rapid 60% decrease in [Ca2+](i). The addition of 1 pM to 1 mu M ANG II immediately after 1 mu M ANP caused an increase in [Ca2+](i) which never exceeded the basal level in the absence of ANP. The data indicate that ANG II increases cell [Ca2+](i), as expected, and provide the new observation that ANP reduces [Ca2+](i) in these ce lls. Furthermore, ANP reduces the increase in [Ca2+](i) elicited by AN G II, thus modulating the effect of ANG II on [Ca2+](i).