Mechanisms of cGMP-dependent mesangial-cell relaxation: a role for myosin light-chain phosphatase activation

Abstract

Although the cGMP-dependent relaxation of contractile cells seems to depend on the ability of the cyclic nucleotide to interfere with intracellular calcium, this does not appear to be the only mechanism involved. The present experiments were designed to analyse alternative mechanisms, trying to test the hypothesis that cGMP could relax rat mesangial cells by activating myosin light-chain phosphatase (MLC-PP), with the subsequent dephosphorylation of myosin light chain (MLC). The effect of a cGMP analogue, dibutyryl cGMP (dbcGMP), on angiotensin II-(AII) and PMA-induced MLC phosphorylation (MLCP) was tested, in the presence of calyculin A (CA), an inhibitor of MLC-PP. MLCP was measured, after cell labelling with (32)P, by immunoprecipitation. dbcGMP prevented the increased MLCP induced by AII or PMA, and this inhibition was blocked by CA. dbcGMP also increased the MLC dephosphorylation observed in cells incubated with AII and in which MLC kinase and protein kinase C activities were blocked. The AII-elicited increased intracellular calcium concentration was only partially inhibited by dbcGMP. These results suggest that the cGMP-induced mesangial-cell relaxation could be due, at least partially, to the stimulation of MLC-PP.

Differential relaxing responses to particulate or soluble guanylyl cyclase activation on endothelial cells: a mechanism dependent on PKG-Iα activation by NO/cGMP

“…Every cell with a sharp margin suitable for the planimetric analysis was considered, and 6-12 cells were analyzed per photograph. Planar cell surface area (PCSA) was determined by computer aid planimetric techniques (17,35). Measurements were performed by two different researchers in a blind fashion.…”

Nitric Oxide-Induced Decrease in Calcium Sensitivity of Resistance Arteries Is Attributable to Activation of the Myosin Light Chain Phosphatase and Antagonized by the RhoA/Rho Kinase Pathway

“…2 Recent studies in other preparations also challenged the classical model of action for NO. 4,6,19,20 However, the cellular mechanism of NO-induced, Ca 2ϩ -independent dilations in microvessels remains unclear. Wu et al 3 demonstrated Ca 2ϩ -independent relaxations by 8-Br-cGMP in skinned rabbit ileum smooth muscle that were based on activation of MLCP.…”

“…Accordingly, cGMPdependent relaxations of mesangial cells were also shown to depend on MLCP activation. 4 Recently, Surks et al 5 provided a possible molecular basis demonstrating that cGKI␣, which finally mediates the effects of NO and cGMP, is targeted to the contractile apparatus by a leucine zipper interaction with the MLCP myosin-binding subunit.…”

“…In the aforementioned study, MLCP was activated by cGMP, the intracellular second messenger of NO. More recent studies have shown that cGMP/cGMP-dependent kinase (cGKI␣)-dependent activation of MLCP also occurs in cultured mesangial, 4 VSMCs, 5 and intact arterial smooth muscle, 6 suggesting that the NOinduced reduction of Ca 2ϩ sensitivity observed in RA could indeed result from an increase in MLCP activity. Additional evidence for a potential role of MLCP in controlling microvascular tone comes from an earlier study in which we showed that oxidized low-density lipoproteins (oxLDLs) induced contraction by increasing the myofilament Ca 2ϩ sensitivity via a RhoA/Rho kinase-dependent mechanism.…”

Effects of Maturation on Mechanisms of cGMP-Induced Cerebral Vasodilatation

“…PKG can decrease cytosolic calcium by increasing calcium efflux and calcium uptake into the sarcoplasmic reticulum [21,22]. PKG can also induce vasodilatation by decreasing myofilament calcium sensitivity through phosphorylation of proteins such as telokin [23,24], myosin light chain phosphatase [24,25], Rho kinase [26] and possibly SM22-· [27].…”