Regulation of myogenic tone in cerebral and mesenteric resistance arteries by metabolic agents and second messenger systems

Routledge, Hayden Swailes (2000) Regulation of myogenic tone in cerebral and mesenteric resistance arteries by metabolic agents and second messenger systems. PhD thesis, University of Glasgow.

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Abstract

1. The pressure-perfusion myograph. permeabilisation techniques and also
intracellular membrane potential recordings were used to examine the
regulation of myogenic tone in cerebral and mesenteric resistance
arteries by metabolic agents and second messenger systems.
2. After pressurisation to 60 mmHg, rat isolated mesenteric and cerebral
resistance arteries developed spontaneous myogenic tone, resulting in a
26 ± 1% (n = 42) and 30 ± 2% (n = 14) reduction in diameter
respectively.
3. The metabolic vasodilator adenosine and the KATI' channel opener
cromakalim each produced a dose-dependent dilatation of pressurised
mesenteric arteries. The cromakalim-evoked dilatation was inhibited by
glibenc1amide (l J.lM), demonstrating the presence of the KATI' channel
in the mesenteric artery and their activation as the mechanism for
cromakalim-evoked dilatation. In contrast neither adenosine nor
cromakalim produced a dilatation of pressurised cerebral arteries.
4. Adenosine-evoked dilatation of mesenteric arteries was unaffected by
the nitric oxide synthase inhibitor L-NAME (100 IlM). antagonists of
the KATI' channel (gJibenclamide; 1 J.lM), the small conductance Ca2'
activated K+ channel (apamin; 0.3 J.lM) and the large conductance, Ca2!
activated K+ channel (TEA; 1 mM). Further to this, cromakalim (10
IlM) but not adenosine (100 J.lM) produced a hyperpolarisation of the
pressurised mesenteric artery. This suggests that neither nitric oxide
synthesis nor K+ channel activation contributed to the adenosine-evoked
dilatation.
5. Adenosine evoked adose-dependent dilatation of p-escin permeabilised
mesenteric arteries; where the intracellular Ca" concentration was clamped to ~600 nM. The mechanism of adenosine-evoked dilatation
may involve a decreased myofilament Ca2+ sensitivity.
6. An increase in extracellular potassium ion concentration ([K+lo) may
link increased neuronal activity and regional cerebral blood flow.
Elevation of [K+Jofrom 4.7 to 10 mM evoked a sustained dilatation of
isolated pressurised thalamo-perforating cerebral arterioles.
7. The K+-evoked dilatation was inhibited by the inward rectifier K+
channel (K1R) inhibitor Ba2+ (50J.lM), and the K+ channel inhibitor
cesium (20mM) but was not blocked by inhibitors of the ATP-sensitive
(KATP)and the Ca2
+ -activated K+ channel (KcJ, glibenclamide (l J.lM)
and TEA (lmM) respectively. Nor was the dilatation altered with the
neurotoxin tetrodotoxin (TTX, 0.3 J.lM). The K+--evoked dilatation was
associated with a membrane hyperpolarisation to -58 ± I mV (n = 5),
from a control value of -42 ± 1 mV (n = 10).
8. It is proposed that increased [K+Jo evokes a dilatation of thalamoperforating
cerebral arteries via an activation of KIR channels and
smooth muscle cell hyperpolarisation.
9. An increase in [Ca2+]o to approximately 700 nM evoked a 30 ± 3 % (n =
28) constriction of isolated ~-escin permeabilised cerebral resistance
arteries.
10. Under [Ca2+1 clamped conditions the putative PKC activator indolactam
evoked a 20 ± 2% constriction of the artery. The PKC inhibitor (PKC(19_
36); I IlM) produced a near maximal (85 ± 4 %) reversal of the
indolactam-evoked constriction of the artery, while PKC(19_36) (1 IlM)
produced only a minor (12 ± 3 %) reversal of the Ca2+-induced
constriction, thus confirming that the indolactam-evoked constriction
was due to an activation ofPKC.

11. The MLCK antagonist SM-l (100 JlM) reversed both the Ca2+_ and the
indolactam-evoked constriction of the artery. The calmodulin antagonist
RS-20 (0.1 - 100 JlM) dose-dependently reversed the Ca2
+ -evoked
constriction but, even up to a concentration of 300 JlM, did not reverse
the indolactam evoked-constriction of the artery.
12. It is proposed that MLCK but not calmodulin plays a role in the PKCevoked
smooth muscle contraction.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QP Physiology
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: McCarron, Dr. John
Date of Award: 2000
Depositing User: Ms Mary Anne Meyering
Unique ID: glathesis:2000-4904
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2014 10:14
Last Modified: 30 Jan 2014 11:59
URI: http://theses.gla.ac.uk/id/eprint/4904

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