The involvement of phosphorylation of myosin phosphatase targeting subunit 1 (MYPT1) and MYPT1 isoform expression in NO/cGMP mediated differential vasoregulation of cerebral arteries compared to systemic arteries

Aim Constitutive release of NO blunts intrinsic and stimulated contractile activity in cerebral arteries ( CA ). Here, we explored whether phosphorylation and expression levels of the PKG ‐sensitive, leucine zipper positive ( LZ + ) splice variants of the regulatory subunit of myosin phosphatase ( MYPT 1) are involved and whether its expression is associated with higher cGMP sensitivity. Methods Vascular contractility was investigated by wire myography. Phosphorylation of MYPT 1 was determined by Western blotting. Results Constitutive phosphorylation of MYPT 1‐T696 and T853 was lower and that of S695 and S668 was higher in cerebral arteries from the circulus arteriosus ( CA ‐w) than in femoral arteries ( FA ), while total MYPT 1 expression was not different. In CA ‐w but not in FA , L‐ NAME lowered phosphorylation of S695/S668 and increased phosphorylation of T696/T853 and of MLC 20 ‐S19, plus basal tone. The increase in basal tone was attenuated in CA ‐w and basilar arteries ( BA ) from heterozygous MYPT 1‐T696A/+ mice. Compared to FA , expression of the LZ + ‐isoform was ~2‐fold higher in CA ‐w coincident with a higher sensitivity to DEA ‐ NONO ate, cinaciguat and Y27632 in BA and 8‐Br‐ cGMP (1 μmol/L) in pre‐constricted ( pC a 6.1) α‐toxin permeabilized CA s. In contrast, 6‐Bnz‐ cAMP (10 μmol/L) relaxed BA and FA similarly by ~80%. Conclusion Our results indicate that (i) regulation of the intrinsic contractile activity in CA involves phosphorylation of MYPT 1 at T696 and S695/S668, (ii) the higher NO / cGMP / PKG sensitivity of CA s can be ascribed to the higher expression level of the LZ + ‐ MYPT 1 isoform and (iii) relaxation by cAMP / PKA pathway is less dependent on the expression level of the LZ + splice variants of MYPT 1.