Calcium response of single adrenal glomerulosa cells to external potassium.

The cytosolic calcium (Cai2+) response to external potassium (K+) was examined in single rat zona glomerulosa (ZG) cells by monitoring fura-2-fluorescence with microspectrofluorometry and digital imaging microscopy. The majority (68%) of morphologically identified ZG cells demonstrated an increase in Cai2+ during K+ stimulation. Cai2+ rose monotonically from a mean basal level of 232 +/- 15 to 285 +/- 37 nM at 5 mM and 680 +/- 60 nM at 10 mM K+ for responsive ZG cells. The Cai2+ response was largely (greater than 90%) inhibited by nominal zero calcium or 1 mM cadmium and substantially modified in the presence of 10(-5) M nifedipine. The response kinetics were characterized by a rising phase that depended on the size of the Cai2+ change, with larger increases associated with a faster onset. Cai2+ approached a plateau level that was sustained for the duration of K+ stimulation from 1 to 5 min. Cai2+ appeared to be more uniformly distributed across the cell under resting conditions than during stimulation. Assessment of the Cai2+ response in single ZG cells documents 1) a majority, but not all, of ZG cells respond to K+, 2) simple kinetics consisting of a rapid onset and sustained plateau Cai2+ level, 3) a dose-dependent Cai2+ increase in the physiological range of K+, and 4) inhibition by calcium channel blockers and sensitivity to small increases in K+ consistent with activation of low-threshold calcium channels.