Effect of forskolin on endothelin-induced phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells

Prejunctional AT(1) receptor subtype-dependent modification of neurotransmitter releases in canine isolated splenic arteries

1. The regulation by angiotensin II (Ang II) formed locally on nerve-stimulated purinergic and adrenergic components of double-peaked vasoconstrictions in the canine splenic artery and Ang II receptor subtypes involved were investigated. 2. The perfusion of the precursor angiotensin I (Ang I, 0.1-1 nm) did not affect the vasoconstrictor responses to noradrenaline (NA, 0.03-1 nmol) and adenosine 5'-triphosphate (ATP, 0.03-1 micromol). The second component vasoconstrictor response to nerve stimulation was dose dependently potentiated by Ang I (0.1-1 nm). The first peaked constriction was slightly, but insignificantly increased. The potentiating effects of Ang I were abolished by KRH-594 (10 nm), a selective AT(1) receptor antagonist, but not by PD 123319 (1-10 nm), an AT(2) receptor antagonist. KRH-594 (10 nm) or PD 123319 (10 nm) never affected the vasoconstrictions to either NA or ATP. 3. The treatment with KRH-594 (1-10 nm) produced a greater inhibition on the second peaked response than the first one, although both of them were dose dependently inhibited. PD 123319 (1-10 nm) did not affect the vasoconstrictor responses induced by nerve stimulation. 4. Inhibition of angiotensin-converting enzyme with 10 nm enalaprilat reduced the second peaked response, having no significant inhibition on the first peaked response. A higher dose of enalaprilat (100 nm) produced a greater inhibition of the second peak than the first one. It reduced the second peak by approximately 65%, while the first peak was decreased approximately 35%. After treatment with enalaprilat, Ang I (1 nm) failed to enhance the neuronal vascular response. Enalaprilat at doses used did not affect the vasoconstrictions to either NA or ATP. 5. The present results indicate that endogenously generated Ang II may produce a more marked potentiation of adrenergic transmission than purinergic transmission via activation of prejunctional AT(1) receptors.

Modification of transmitter release from periarterial nerve terminals by dipyridamole in canine isolated splenic artery

1. The aim of the present study was to determine the modulatory effects of dipyridamole on purinergic and adrenergic transmission in the canine isolated, perfused splenic artery. 2. Periarterial nerve electrical stimulation readily induced a double-peaked vasoconstriction consisting of an initial transient, predominantly P2X receptor-mediated constriction followed by a prolonged, mainly alpha1-adrenoceptor-mediated response. 3. Exposure of tissues to dipyridamole (0.1-1 micro mol/L) dose-dependently inhibited both the first and second peaks of the vasoconstrictor response at a low frequency of stimulation (1 Hz), whereas at an intermediate frequency of stimulation (4 Hz), the first peak of the response was depressed without any significant effect being observed on the second peak of constriction. 4. At a higher dose (1 micro mol/L) dipyridamole potentiated vasoconstrictor responses to noradrenaline (0.03-1 nmol). At any doses used, dipyridamole had no effect on the vasoconstrictor responses to ATP (0.03-1 micro mol). 5. Tyramine (0.01-0.3 micro mol) induced vasoconstriction in a dose-dependent manner. The dose-response curves for tyramine were shifted to the right following treatment with dipyridamole (0.1-1 micro mol/L). 6. The present results indicate that dipyridamole may inhibit purinergic and adrenergic transmission presynaptically, whereas postsynaptically dipyridamole may potentiate the adrenergic vascular constriction by inhibition of transmitter uptake.

Mechanisms of release of ATP from vascular purinergic nerves

1. The vasoconstrictor response to periarterial nerve electrical stimulation (PNS) and neurotransmission by ATP are discussed and illustrated, using canine isolated and perfused splenic arterial preparations. 2. The conditions for appearance of dominant purinergic constrictor response to PNS are discussed. 3. Modulation of the purinergic vasoconstrictor responses to PNS by several kinds of presynaptic receptor agonists and antagonists is reviewed. 4. Influences of purinergic responses to PNS by guanethidine, reserpine, tetrodotoxin (TTX) or omega-conotoxin GVIA (omegaCTX) are also reviewed. 5. Effects of imipramine and removal of the endothelium are discussed. 6. Evidence is presented for selective inhibition of purinergic responses to PNS by an adequate cold storage of the vessel. 7. The roles of ATP released by PNS in isolated canine splenic arteries are proposed.

Pharmacological analysis of functional neurovascular transmission in canine splenic arteries: role of neuropeptide Y

1 The effects of neuropeptide Y (NPY) upon the isolated vasculature are reviewed. 2 The vasconstrictor responses to periarterial nerve stimulation (PNS) and neurotransmission by noradrenaline (NA) and ATP are discussed and illustrated using canine isolated perfused splenic artery. 3 Modulation of the vascular responses to PNS by NPY via pre- and post-junctional NPY Y2 and Y1 receptors is discussed. 4 Evidence is presented for different alpha1-adrenoceptor subtypes mediating vasoconstriction to exogenous and endogenously released NA and their different locations in the neurovascular junction and extrajunctional regions. 5 Activation of NPY Y1-receptors potentiates sympathetic nerve activated alpha1-adrenoceptor vasoconstriction. The proposal that the postjunctional alpha1B adrenoceptor may be linked to the NPY Y1-receptor and is responsible for co-operation between sympathetic and NPYergic interactions in the vasculature is discussed.

Cross talk between cyclic nucleotides and polyphosphoinositide hydrolysis, protein kinases, and contraction in smooth muscle

This article provides an update of a minireview published in 1996 (Abdel-Latif AA. Proc Soc Exp Biol Med 211:163-177, 1996), the purpose of which was to examine in nonvascular smooth muscle the biochemical and functional cross talk between the sympathetic nervous system, which governs the formation of cAMP and muscle relaxation, and the parasympathetic nervous system, which governs the generation of IP3 and diacylglycerol, from the polyphosphoinositides, Ca2+ mobilization, and contraction. This review examines further evidence, both from nonvascular and vascular smooth muscle, for cross talk between the cyclic nucleotides, cAMP and cGMP via their respective protein kinases, and the Ca2+-dependent- and Ca2+-independent-signaling pathways involved in agonist-induced contraction. These include the IP3-Ca2+-CaM- myosin light chain kinase (MLCK) pathway and the Ca2+-independent pathways, including protein kinase C-, MAP kinase-, and Rho-kinase. In addition, MLC phosphorylation and contraction can also be increased by a decrease in myosin phosphatase activity. A summary of the cross talk between the cyclic nucleotides and these signaling pathways was presented. In smooth muscle, there are several targets for cyclic nucleotide inhibition and consequent relaxation, including the receptor, G proteins, phospholipase C-beta1-4 isoforms, IP3 receptor, Ca2+ mobilization, MLCK, MAP kinase, Rho-kinase, and myosin phosphatase. While significant progress has been made in the past four years on this cross talk, the precise mechanisms underlying the biochemical basis for the cyclic nucleotide inhibition of Ca2+ mobilization and consequently muscle contraction remain to be established. Although it is well established that second-messenger cross talk plays an important role in smooth muscle relaxation, the many sources which exist in smooth muscle for Ca2+ mobilization, coupled with the multiple signaling pathways involved in agonist-induced contraction, contribute appreciably to the difficulties found by many investigators in identifying the targets for cyclic nucleotide inhibition and consequent relaxation. Better methodology and more novel interdisciplinary approaches are required for elucidating the mechanism(s) of cAMP- and cGMP-inhibition of smooth muscle contraction.

Differential blocking effects of tetrodotoxin on double-peaked vasoconstrictor responses to periarterial nerve stimulation in canine isolated, perfused splenic artery

1. In the present study, we investigated the effects of progressive inhibition of neuronal sodium channels by increasing concentrations of tetrodotoxin (TTX; 1-30 nmol/L) on the double-peaked vasoconstrictor responses to electrical periarterial nerve stimulation in the canine isolated and perfused splenic artery. 2. Double-peaked vasoconstrictions (biphasic vasoconstrictor responses) were consistently observed in following electrical stimulation with 30 s trains of pulses at 1-10 Hz. At low frequencies of stimulation (1-3 Hz), a submaximal concentration of 3 nmol/L TTX had no effect on the first phase of the contractile response, but almost completely inhibited the second-phase response. At high frequencies (6-10 Hz), the two vasoconstrictor phases were almost equally inhibited by 50% by 3 nmol/L TTX. A three-fold increase in the concentration of TTX used (10 nmol/L) abolished the second-phase vasoconstriction at all stimulation frequencies tested, whereas this concentration of TTX failed to block the first-phase response. Further increasing the concentration of TTX to 30 nmol/L completely blocked the remaining first-phase response. 3. Treatment with 0.1 mumol/L prazosin did not modify the first-phase response to any of the stimulation frequencies in the presence of 3 nmol/L TTX. Moreover, 0.1 mumol/L prazosin had no affect on the second-phase response at low frequencies (1-3 Hz), while at high frequencies (6-10 Hz) it slightly, but significantly inhibited the second-phase response. The vasoconstrictor responses that persisted after 3 nmol/L TTX and 0.1 mumol/L prazosin were completely suppressed by subsequent application of 1 mumol/L alpha, beta-methylene ATP at all stimulation frequencies (1-10 Hz). 4. In conclusion, progressive inhibition of sodium channels by increasing the concentration of TTX may exert a more preferential inhibition on adrenergic rather than purinergic components, suggesting that TTX-sensitive sodium channels may have a more important role in determining the adrenergic rather than purinergic transmission of sympathetic nerves.