Interactions between neuropeptide Y and the adenylate cyclase pathway in rat mesenteric small arteries: role of membrane potential

Abstract

Simultaneous measurements of membrane potential and tension were performed to investigate the intracellular mechanisms of neuropeptide Y (NPY) in rat mesenteric small arteries. NPY (0.1 μM)depolarized arterial smooth muscle cells from −55 to −47 mV and increased wall tension by 0.22N m−1, representing 11% of the contraction elicited by a high potassium solution. Isoprenaline (1 μM) and acetylcholine (1 μM) evoked hyper polarizations of 11 and 17 mV, resupectively. NPY inhibited the isoprenaline ‐induced effects on membrane potential without affecting those of acetylcholine. Forskolin evoked sustained concentration‐dependent hyper polarizations of small mesenteric arteries. NPY (0.1 mM) inhibited the resuponses to 1 μM forskolin, but did not alter the stable hyperpolarization elicited by the supecific activator of protein kinase A (PKA) SP‐5,6‐DCl‐cBIMPS (0.1 mm). Forskolin increased the cyclic AMP (cAMP) content of the arteries 21‐fold, and NPY inhibited the forskolin‐evoked increase in cAMP levels by 91 %. The hyperpolarization produced by 1 μM forskolin was not affected by either charybdotoxin (0.1 μM) or 4‐aminopyridine (0.5mM), but glibenclamide (5 μM) inhibited the hyperpolarization by 70%. Glibenclamide also inhibited the hyperpolarization evoked by SP‐:5,6‐DCl‐cBIMPSuby59%. Neither depolarization nor contraction caused by NPY were significantly affected by either glibenclamide (5 μM) or nifedipine (1 μM), but they were reduced by gadolinium (10 μM). However, the blocking effect of NPY on forskolin‐elicited hyperpolarization was not affected by gadolinium. Charybdotoxin (O.1 μM) and 4‐aminopyridine (0.5 mM) strongly enhanced the depolarization and contraction caused by NPY (O.1μM), and nifedipine (1 μM) prevented the enhanced resuponses to NPY in the presence of charybdotoxin. These findings suggest that NPY acts through at least two different intracellular mechanisms in mesenteric small arteries: a depolarization of arterial smooth muscle which is probably due to activation of non‐selective cation channels, and a marked inhibition of adenylate cyclase activity, which in turn inhibits the hyperpolarization produced by cAMP accumulation in these arteries.

Physiological regulation of penile arteries and veins

“…The Y 1 receptor is a G-protein-coupled receptor that usually enhances other constrictors responses in small arteries by depolarizing arterial smooth muscle and by inhibiting cyclic adenosine monophosphate (cAMP)-mediated relaxations. 28,29 Under conditions of Y 1 and Y 2 receptor blockade, NPY can also induce NO-independent relaxations in penile resistance arteries through atypical receptors located at the endothelium, which could account for the in vivo proerectogenic effects reported for the peptide. 26 …”

A study of NPY‐mediated contractions of the porcine isolated ear artery

“…A recent study in rat mesenteric small arteries also supports the view that NPY can elicit contractions through two independent pathways, although the study did not examine NPY responses after pre-contraction with another agonist (Prieto et al, 1997). The ®rst pathway involves the ability of NPY to inhibit forskolin-stimulated cyclic AMP formation, and, therefore, prevents the e ects of cyclic AMP accumulation on membrane potential.…”

“…The ®rst pathway involves the ability of NPY to inhibit forskolin-stimulated cyclic AMP formation, and, therefore, prevents the e ects of cyclic AMP accumulation on membrane potential. The second pathway involves a direct depolarization of the arterial smooth muscle through activation of gadolinium-sensitive cation channels (Prieto et al, 1997). NPY is also able to increase [Ca 2+ ] i in an adenylyl cyclase-independent manner (Erdbrugger et al, 1993;Mihara et al, 1989), although this is thought to be mediated through a Y 3 -like receptor (Erdbrugger et al, 1993).…”

“…NPY activates a number of intracellular responses in isolated blood vessels and vascular smooth muscle cells maintained in culture, including an inhibition of adenosine 3' : 5'-cyclic monophosphate (cyclic AMP) production (Fredholm et al, 1985;Prieto et al, 1997), an increase in [Ca 2+ ] i (Erdbrugger et al, 1993;Mihara et al, 1989), and membrane depolarization (Prieto et al, 1997). However, the precise relationship between these responses and NPY-induced vasoconstriction is unclear.…”

Heterogeneity of the neuropeptide Y (NPY) contractile and relaxing receptors in horse penile small arteries

“…Therefore, the present results demonstrate the involvement of a heterogeneous population of NPY Y 1 and Y 2 receptors in the vasoconstrictor responses of NPY in penile small arteries. NPY has traditionally been regarded as a sympathetic vasoconstrictor, which usually induces indirect contractions by either enhancing other vasoconstrictors responses or by inhibiting vasodilatation (Edvinsson et al, 1984;Prieto et al, 1991;1997a;Malmstro¨m, 1997;Michel et al, 1998). However, evidence has emerged recently suggesting a vasodilator role for the peptide in certain vascular beds both in vivo and in vitro models.…”