Nitric oxide donors modify free intracellular calcium levels in rat anterior pituitary cells

The effect of nitric oxide donors on intracellular calcium concentration [C a2+](i) was studied in anterior pituitary cells using ratiometric FURA 2 fl uorescence measurements. Sodium nitroprusside (NP) induced a transient decr ease in [Ca2+](i), after which [Ca2+](i) returned to, or even increased ove r basal values. S-Nitroso glutathione (GSNO) induced a similar decrease. NP also inhibited high [Ca2+](i) achieved by depolarization with 25 mM K+. Th e inhibitory effect of NP was partially blunted by pretreatment with methox y-verapamil, and in calcium free buffer, and was not altered by thapsigargi n. Interestingly, in calcium free buffer there was a significant stimulator y effect of NP, which was partially blunted by thapsigargin. We conclude th at NO donors modify [Ca2+](i) in anterior pituitary cells. The action is bi phasic, with an initial decrease in [Ca2+](i) probably related to a decreas e of Ca2+ influx through VDCC, and an increase evidenced in calcium free bu ffer in which the inhibitory component is absent, and partially depends on thapsigargin sensitive calcium stores. (C) 1998 Elsevier Science Ireland Lt d. All rights reserved.