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Excitation-contraction coupling in the human saphenous vein Crowley, Christine Maureen


Background: Human vascular preparations are most suitable to study vascular physiology and pathophysiology. Fresh tissues are difficult to obtain and may be damaged from the surgical procedure, limiting their use or introducing variability in the experimental findings. The purpose of this study was two-fold: (1) to demonstrate that a functional human saphenous vein (HSV) preparation may be obtained from coronary artery revascularisation procedures; (2) to elucidate excitation-contraction coupling mechanisms in functionally intact segments of HSV. Methods: Isometric contraction experiments were performed using contractile stimuli, such as high K⁺ depolarising solution (high K⁺) and the α₁-adrenergic agonist phenylephrine (PE), and an endothelium-dependent vasodilator, acetylcholine (ACh). Contraction was also combined with in situ smooth muscle intracellular Ca²⁺ ([Ca²⁺][sub i]) imaging by confocal microscopy in HSV stimulated by high K⁺ and PE. Results & Conclusions: HSV segments that were undistended showed far greater responsiveness to contractile and relaxing stimuli than portions of HSV segments that were distended and surgically prepared. Hence, all subsequent experiments were performed on undistended HSV segments. High K⁺ elicited a sustained rise in [Ca²⁺][sub i] and contraction. Contractions in nominally Ca²⁺-free physiological salt solution (PSS) were not attenuated and decayed many orders of magnitude slower in the HSV than in animal vascular preparations. High K⁺ contractions in both normal and nominally Ca²⁺-free PSS were nearly completely blocked by the Ca²⁺ antagonist nifedipine. These results suggest the presence of an extracellular source of tightly bound Ca²⁺ in HSV segments. Stimulation of HSV segments with PE resulted in a transient rise in [Ca²⁺]i that returned to baseline during sustained contractions. Nominally Ca²⁺-free PSS, pre-incubation with nifedipine or the non-specific cation channel blocker SK&F 96365, significantly depressed the maximum amplitude of these contractions. The sustained phase of the contraction was not sensitive to Ca²⁺ antagonists, but was attenuated by Ca²⁺ removal, suggesting Ca²⁺ influx through the leak pathway during this phase. The rho kinase inhibitor HA-1077 completely abolished while the tyrosine kinase inhibitor genistein only attenuated the plateau phase. Protein kinase C and mitogen-activated protein kinase were not involved. Hence, calcium, rho kinase and tyrosine phosphorylation mediate PE contractions in the HSV.

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