Atriopeptins decrease resting and hormone-elevated cytosolic Ca in cultured mesangial cells.

The purpose of this work was to investigate the effects of atrial peptides on the cytosolic Ca levels of cultured, adherent, mesangial cells. Resting Ca levels, measured by the use of fura-2, were dose-dependently decreased by up to 30%, by atriopeptin 23. The half-maximal effect was elicited by approximately 30 pM atriopeptin-23. Atriopeptin 21 also decreased resting Ca levels by up to 30%, but this peptide was approximately 30-fold less potent than atriopeptin 23. Atriopeptin 23 (100 nM) inhibited both the Ca transient and the peak Ca value elicited by 1 nM vasopressin, but the atrial peptide had no significant effect on the Ca transient elicited by higher vasopressin concentrations. At concentrations lower than 100 nM, atriopeptin 23 had no effect on the vasopressin-induced Ca transient. Atriopeptin 23 also decreased the Ca transient and the peak Ca value elicited by 100 nM angiotensin II. Similar to vasopressin, the angiotensin II-induced Ca transient was inhibited by 100 nM but not lower concentrations of atriopeptin 23. In contrast to the effect of atriopeptin 23, atriopeptin 21 (100 nM) had no effect on the Ca transient elicited by vasopressin. These results demonstrate that atriopeptins function as modulators of resting and, under certain conditions, of hormone-increased Ca levels in cultured mesangial cells.