This study was performed to test the hypothesis that endothelin peptides di
fferentially influence intracellular calcium concentration ([Ca2+](i)) in p
reglomerular microvascular smooth muscle cells (MVSMC), in part through act
ivation of endothelin (ET)(A) receptors. Experiments were performed in vitr
o with the use of single MVSMC freshly isolated from rat preglomerular micr
ovessels. The effect of ET-1, ET-2, and ET-3 on [Ca2+](i) was measured with
the use of the calcium-sensitive dye, fura 2, and standard fluorescence mi
croscopy techniques. Baseline [Ca2+](i) averaged 84+/-3 nmol/L (n=141 cells
from 23 dispersions). ET-1 concentrations of 1, 10, and 100 nmol/L, evoked
peak increases in [Ca2+](i) of 48 +/- 16, 930 +/- 125, and 810 +/- 130 nmo
l/L, respectively. The time course of the [Ca2+](i) response was biphasic,
beginning with a rapid initial increase followed by a sustained plateau pha
se or a period during which. [Ca2+](i) oscillated sharply. Similar response
s were observed after ET-2 administration, In contrast, ET-3 stimulated mon
ophasic increases in [Ca2+](i) of only 14 +/- 5, 33 +/- 16, and 44 +/- 19 n
mol/L at peptide concentrations of 1, 10, and 100 nmol/L, respectively. The
se responses are significantly smaller than responses to ET-1 or ET-2, resp
ectively. The relative contributions of calcium mobilization and calcium in
flux in the response to ET-1 were also evaluated. Removal of calcium from t
he bathing medium did not significantly alter the peak response to 10 nmol/
L ET-1 but abolished the late phase elevation of [Ca2+](i). These data demo
nstrate that endothelin peptides increase [Ca2+](i) in preglomerular MVSMC.
The concentration-response profiles are consistent with the response invol
ving activation of ETA receptors. Furthermore, these results suggest that E
T-1 increases [Ca2+](i) by stimulating both the release of intracellular ca
lcium and the influx of calcium from the extracellular medium.