Intracellular angiotensin II activates rat myometrium

Abstract

Angiotensin II is a modulator of myometrial activity; both AT1and AT2receptors are expressed in myometrium. Since in other tissues angiotensin II has been reported to activate intracellular receptors, we assessed the effects of intracellular administration of angiotensin II via microinjection on myometrium, using calcium imaging. Intracellular injection of angiotensin II increased cytosolic Ca2+concentration ([Ca2+]i) in myometrial cells in a dose-dependent manner. The effect was abolished by the AT1receptor antagonist losartan but not by the AT2receptor antagonist PD-123319. Disruption of the endo-lysosomal system, but not that of Golgi apparatus, prevented the angiotensin II-induced increase in [Ca2+]i. Blockade of AT1receptor internalization had no effect, whereas blockade of microautophagy abolished the increase in [Ca2+]iproduced by intracellular injection of angiotensin II; this indicates that microautophagy is a critical step in transporting the peptide into the endo-lysosomes lumenum. The response to angiotensin II was slightly reduced in Ca2+-free saline, indicating a major involvement of Ca2+release from internal stores. Blockade of inositol 1,4,5-trisphosphate (IP3) receptors with heparin and xestospongin C or inhibition of phospholipase C (PLC) with U-73122 abolished the response to angiotensin II, supporting the involvement of PLC-IP3pathway. Angiotensin II-induced increase in [Ca2+]iwas slightly reduced by antagonism of ryanodine receptors. Taken together, our results indicate for the first time that in myometrial cells, intracellular angiotensin II activates AT1-like receptors on lysosomes and activates PLC-IP3-dependent Ca2+release from endoplasmic reticulum; the response is further augmented by a Ca2+-induced Ca2+release mechanism via ryanodine receptors activation.