Role of calcium-dependent potassium channels and mitochondria in the EDHF phenomenon

Charisis, Ioannis 2008. Role of calcium-dependent potassium channels and mitochondria in the EDHF phenomenon. PhD Thesis, Cardiff University.

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Abstract

Background Acetylcholine (ACh) and the calcium ionophore A23187 are both known to trigger EDHF-type responses in the rabbit iliac artery via endothelial cell hyperpolarization mediated by the opening of calcium-dependent potassium channels (Kca). In addition, ACh and A23187 also stimulate the release of hydrogen peroxide (H2O2) from the endothelium. Aims of study 1) To determine the relative contribution of different Kca channel subtypes to ACh- and A23187-evoked responses. 2) To determine whether there is a connection between the activation of endothelial Kca channels and the release of H2O2. 3) To identify the source of endothelium-derived H2O2 in the rabbit iliac artery. Major findings 1) Immimohistochemical investigations demonstrated expression of SKca, IKca and BKca channels in the endothelium of rabbit iliac arteries. 2) Mechanical studies with the SKca inhibitor apamin, the IKca inhibitor l- (2- chlorophenyl)diphenylmethyl -lH-pyrazole (TRAM-34) and the BKca inhibitor iberiotoxin demonstrated that all three Kca channel subtypes participate in ACh- and A23187-evoked EDHF-type relaxations. 3) Mechanical investigations with catalase and the catalase/SOD-mimetic manganese porphyrin (MnTMPyP) demonstrated that responses to ACh and A23187 both included a significant H2C>2-dependent component, that could be inhibited by combined Kca channel blockade. 4) Investigations with the NADPH oxidase inhibitor apocynin, the xanthine oxidase inhibitor oxypurinol and the inhibitors of the mitochondrial electron transport chain rotenone and myxothiazol indicated that mitochondria are likely to be the main source of H2O2 in the endothelium of the rabbit iliac artery. Conclusions The study has highlighted the concerted role of different Kca channel subtypes in ACh- and A23187-evoked EDHF-type relaxations in rabbit iliac arteries. It has also demonstrated that both responses consist of an H202-dependent component which is attenuated when Kca channels are inhibited. However, the evidence provided is not sufficient to prove that H2O2 release in the endothelium is coupled to Kca activation Additional studies aimed to identify the intracellular compartment that produces H2O2 upon stimulation with ACh and A23187. It has been demonstrated that under the current experimental conditions the most likely source of H2O2 is the mitochondrial electron transport chain.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Medicine
Subjects:	R Medicine > R Medicine (General)
ISBN:	9781303184666
Date of First Compliant Deposit:	30 March 2016
Last Modified:	09 Jan 2018 23:14
URI:	https://orca.cardiff.ac.uk/id/eprint/55773

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