Calcium oscillations in single adrenal glomerulosa cells stimulated by angiotensin II

Abstract

The cytosolic calcium (Ca2+i) response to angiotensin II (Ang II) was examined in single rat zona glomerulosa cells by monitoring fura-2 fluorescence with microspectrofluorimetry. Ang II concentrations ranged from 5 X 10(-12) to 5 X 10(-8) M. The mean peak Ca2+i increase was similar at all Ang II concentrations (205 +/- 11 nM), with a significant difference (P less than 0.05) found only between 5 X 10(-12) M (151 +/- 16 nM) and 5 X 10(-9) M (236 +/- 24 nM). Striking differences over the range of Ang II concentrations were found in the Ca2+i response kinetics. A dose-dependent delay of the onset of the Ca2+i response was observed ranging from 2.6 +/- 0.3 sec at 5 X 10(-8) M to 181 +/- 27 sec at 5 X 10(-12) M Ang II. After the delay, cells typically responded with an abrupt increase in Ca2+i, complete within 15 sec. At low Ang II concentrations (5 X 10(-11) and 5 X 10(-12) M), a complex response was often observed consisting of Ca2+i oscillations. Higher Ang II concentrations gave some evidence of Ca2+i oscillation, especially at 5 X 10(-10) M where oscillations appeared fused. Above 5 X 10(-10) M Ang II, the initial Ca2+i increase decayed to an apparent steady-state value 38-40% of the peak response within 5 min; 5 X 10(-10) M Ang II produced a smaller decline to 63% of the initial Ca2+i increase. In contrast to cell population studies, assessment of individual glomerulosa cells demonstrates (i) a dose-dependent delay prior to a rapid increase in Ca2+i; (ii) a similar peak increase at most Ang II concentrations; (iii) greater sensitivity of the Ca2+i response; and (iv) a complex oscillating Ca2+i response in the physiological range of Ang II.