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

Abstract The effect of nitric oxide donors on intracellular calcium concentration [Ca 2+ ] i was studied in anterior pituitary cells using ratiometric FURA 2 fluorescence measurements. Sodium nitroprusside (NP) induced a transient decrease in [Ca 2+ ] i , after which [Ca 2+ ] i returned to, or even increased over basal values. S -Nitroso glutathione (GSNO) induced a similar decrease. NP also inhibited high [Ca 2+ ] i achieved by depolarization with 25 mM K + . The inhibitory effect of NP was partially blunted by pretreatment with methoxy-verapamil, and in calcium free buffer, and was not altered by thapsigargin. Interestingly, in calcium free buffer there was a significant stimulatory effect of NP, which was partially blunted by thapsigargin. We conclude that NO donors modify [Ca 2+ ] i in anterior pituitary cells. The action is biphasic, with an initial decrease in [Ca 2+ ] i probably related to a decrease of Ca 2+ influx through VDCC, and an increase evidenced in calcium free buffer in which the inhibitory component is absent, and partially depends on thapsigargin sensitive calcium stores.