EFFECTS OF ATRIAL NATRIURETIC FACTOR ON CYCLIC GMP CONTENT IN THE RAT AORTIC SMOOTH MUSCLE: STUDIES ON THE ROLE OF MEMBRANE Na⁺,K⁺‐ATPase

Abstract

1. These studies were conducted to determine whether preservation of the functional integrity of the membrane, Na+,K+-stimulated ATPase is essential for the atrial natriuretic factor (r-ANF-8-33) to enhance guanosine 3',5'-monophosphate (cGMP) content in the rat aortic smooth muscle. In freshly dissected rat aortic tissues, levels of cGMP were estimated using radioimmunoassay. 2. ANF (0.1 mumol/L in Krebs-Henseleit media) produced significant elevation in cGMP levels in the aortic smooth muscle when compared with that incubated in the control media, whereas suppression of Na+-pump with ouabain (1.0 mmol/L) and/or K+-free media did not produce any significant changes in the basal cGMP level; these two experimental manoeuvres did not prevent enhancement of cGMP by ANF. 3. Incubation of the tissues in the media containing ouabain plus vasoconstrictor concentrations of norepinephrine (0.3 mumol/L) also did not alter basal cGMP levels and did not prevent the ability of ANF to elevate cGMP. 4. These studies demonstrate that the antagonism by ouabain, of vasorelaxant effects of ANF (as reported in the literature) are not due to the prevention of the ability of ANF to enhance cGMP levels in the arterial smooth muscle. It is proposed that such an antagonism may be related to the actions of ouabain and ANF on diverse, and perhaps independent, mechanisms which affect Ca2+-fluxes across the cell membrane.

ANP Differentially Modulates Marinobufagenin-Induced Sodium Pump Inhibition in Kidney and Aorta

“…30,44 Stimulation of vascular NKA as a consequence of the cGMP-PKG pathway activation has been described in previous experiments. 24,[31][32][33] Our present results demonstrate that the effects of both ppANP and a stable cGMP analog, 8-Br-PET-cGMP, are associated with a dephosphorylation of ␣-1 NKA from aortic sarcolemma and with a loss of its sensitivity to an endogenous ligand, MBG. In the present experiment, a PKG inhibitor, KT5823, partially reversed ppANP-induced dephosphorylation of the NKA from aortic sarcolemma, but the level of phosphorylation remained reduced ( Figure 4D).…”

“…Activation of the guanylyl cyclase-cGMP-protein kinase G (PKG) pathway underlies both renal and vascular effects of ANP peptides. [23][24][25][26] Because cGMP has been reported to regulate activity of the NKA by modulation of its phosphorylation state, 27,28 we also hypothesized that ANP would affect MBG sensitivity of the NKA via modulation of its PKG-dependent phosphorylation. Previously, ANP has been shown to inhibit renal sodium pump, 25,29,30 and both direct and indirect evidence suggest that ANP and/or cGMP can stimulate the sodium pump in the cardiovascular system.…”

“…Previously, ANP has been shown to inhibit renal sodium pump, 25,29,30 and both direct and indirect evidence suggest that ANP and/or cGMP can stimulate the sodium pump in the cardiovascular system. 24,[31][32][33] We, therefore, further hypothesized that, whereas both ANP and MBG exhibit synergistic interaction on renal ␣-1 NKA, ANP would antagonize MBG-induced inhibition of the NKA in vascular sarcolemma.…”

Endogenous Cardiotonic Steroids: Physiology, Pharmacology, and Novel Therapeutic Targets

“…cGMP regulates activity of the Na + /K + -ATPase by modulation of its phosphorylation (Blanco et al, 1998; Fotis et al, 1999) and activation of the guanylyl cyclase-cGMP-PKG pathway underlies both renal and vascular effects of ANPs (Vesely et al, 1987; Hedge et al, 1989; Scavone et al, 1995). Unlike PKC, which directly phosphorylates the Na + /K + -ATPase, the effect of PKG on sodium pump phosphorylation is more complex and involves the recruitment and regulation of additional phosphatases (Aperia et al, 1994; Fotis et al, 1999).…”