ABSTRACT
The effect of angiotensin II (ANG II) and atrial natriuretic peptide (ANP) on intracellular free calcium concentration [ Ca²+]i was investigated in Mandin-Darby canine kidney (MDCK) cells in culture. Changes in [Ca²+]i were monitored fluorometrically with the Ca²+ -sensitive probel fura -2/AM at 37ºC using Perkin-Elmer LS-5 spectrofluorimeter (excitation 340/380 nm,slite 3 nm; emission 520 nm, slit 10 nm). MDCK cells exhibited a mean baseline [Ca²+]i of 98 ñ 10 nM. the addition of increasing concentrations of SNG II (1 pM to 1 µM) to the cell suspension led to a progressive increase in [Ca²+]i to 2-3 times basal levels. In contrast, addition of 1 µM ANP to the cell suspension led to a very rapid 60 percent decrease in [Ca²+]i. The addition of 1 pM to 1 µM ANG II immediately after 1 µM ANP caused an increase in [Ca²+]i which never exceded 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 cells. Further more, ANP reduces the increase in [Ca²+]i elicited by ANG II, thus modulating the effect of ANG II on [Ca²+]i