We thank Dr. William Cashdollar, and the Northwestern Mutual Foundation Imaging Center at the Blood Research Institute of Wisconsin for help with the imaging studies. We also thank Dr. Daria Ilatovskaya for critical reading of this manuscript and helpful discussion. This study was supported by National Institutes of Health Grants HL108880 (to A.S.) and DP2-OD008396 (to A.M.G.).

The experimental procedures described below were approved by the Institutional Animal Care and Use Committee (IACUC) at the Medical College of Wisconsin and were in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.
1. Isolation of the Rat Aorta
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	<li>Anesthetize rats with isoflurane (5% induction, 1.5 to 2.5% maintenance) or another IACUC approved method.</li>
	<li>Place the rat in a supine position. In order to expose the abdominal organ...

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The authors have nothing to disclose.

Experimental Overview. To better understand the contribution of calcium and NO to vascular physiology, a novel method was developed for measuring [Ca2+]i and NO within smooth muscle and endothelial cells of isolated intact aortas. Together, this protocol consists of these critical steps: 1) Mechanical isolation and preparation (not enzymatic digestion) of the vessel. It is important to keep the tissue healthy and intact as much as possible to obtain optimal physiological recordings. 2) Incu...

Calcium is a fundamental second messenger within vascular cells such as endothelial and smooth muscle cells. It is the primary stimulus for vascular contraction and plays a major role in vascular dilation, including its effects through NO generation within the endothelium. Due to limitations of imaging technologies, it has been virtually impossible to observe calcium handling within the intact vessel. The development of two photon imaging systems and the creation of new calcium or NO labeling dyes, makes it possible to image at a sufficient depth and resolution to begin to understand calcium dynamics and NO production within the vasculature.
Two photon microscopy has recently been applied in&#160;tissue, organs and even whole animal studies because of its superior ability to deeply penetrate tissues with low background fluorescence and high signal sensitivity.1,2 The narrow spectrum of two photon excitation at the illumination focal point and the use of non-descanned detectors are the reasons why two photon microscopy is superior to traditional confocal microscopy. Confocal microscopy cannot produce high-quality images at the necessary tissue depth due to the auto-fluorescence and the scattering of out-of-focus light into the confocal pinhole. Consequently, we have developed a method using a two photon microscope to measure [Ca2+]i signaling and NO production in intact, individual blood vessel cells with high resolution and a low signal-to-noise ratio.&#160;

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	<tbody>
		<tr>
			<td>DAF-FM</td>
			<td>Life Technologies</td>
			<td>D-23842</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluo 4 AM</td>
			<td>Life Technologies</td>
			<td>F14217</td>
			<td>500&#181;l in DMSO</td>
		</tr>
		<tr>
			<td>Pluronic F-68 solution</td>
			<td>Sigma-Aldrich</td>
			<td>P5556</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Name</td>
			<td>Tocris</td>
			<td>0665</td>
			<td></td>
		</tr>
		<tr>
			<td>Olympus upright microscope</td>
			<td>Olympus</td>
			<td>Fluoview FV1000</td>
			<td></td>
		</tr>
		<tr>
			<td>MaiTai HP DeepSee-OL&#160;</td>
			<td>Spectra Physics</td>
			<td></td>
			<td>Ti:sapphire laser 690nm &#8212; 1040nm</td>
		</tr>
		<tr>
			<td>Filters</td>
			<td>Olympus</td>
			<td>FV10-MRL/R&#160;</td>
			<td>495 to 540 nm&#160;</td>
		</tr>
		<tr>
			<td>25&#215; water-immersion objective lens</td>
			<td>Olympus</td>
			<td>XLPL25XWMP</td>
			<td>N.A. 1.05 and working distance 2 mm</td>
		</tr>
		<tr>
			<td>Slice Anchor grid&#160;</td>
			<td>Warner Instrument&#160;</td>
			<td>SHD-27LH</td>
			<td></td>
		</tr>
		<tr>
			<td>Other basic reagents&#160;</td>
			<td>Sigma-Aldrich</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

two-photon imaging of intracellular ca2+ handling and nitric oxide production in endothelial and smooth muscle cells of an isolated rat aorta

Calcium is a very important regulator of many physiological processes in vascular tissues. Most endothelial and smooth muscle functions highly depend on changes in intracellular calcium ([Ca2+]i) and nitric oxide (NO). In order to understand how [Ca2+]i, NO and downstream molecules are handled by a blood vessel in response to vasoconstrictors and vasodilators, we developed a novel technique that applies calcium-labeling (or NO-labeling) dyes with two photon microscopy to measure calcium handling (or NO production) in isolated blood vessels. Described here is a detailed step-by-step procedure that demonstrates how to isolate an aorta from a rat, label calcium or NO within the endothelial or smooth muscle cells, and image calcium transients (or NO production) using a two photon microscope following physiological or pharmacological stimuli. The benefits of using the method are multi-fold: 1) it is possible to simultaneously measure calcium transients in both endothelial cells and smooth muscle cells in response to different stimuli; 2) it allows one to image endothelial cells and smooth muscle cells in their native setting; 3) this method is very sensitive to intracellular calcium or NO changes and generates high resolution images for precise measurements; and 4) described approach can be applied to the measurement of other molecules, such as reactive oxygen species. In summary, application of two photon laser emission microscopy to monitor calcium transients and NO production in the endothelial and smooth muscle cells of an isolated blood vessel has provided high quality quantitative data and promoted our understanding of the mechanisms regulating vascular function.

In order to accurately assess the contribution of calcium to vascular physiology (vasodilation and vasoconstriction), a protocol was designed to load calcium dyes into both endothelial cells and smooth muscle cells in isolated intact aortae. The general experimental set up depicted in Figure 1, shows the basic strategy for isolation and preparation of the vessel before imaging. Briefly, after isolation of the aorta from the rat, it should be cleaned of fat and connective tissue and slit longitudinally. T...

Watch this Scientific Journal Video about Two-photon Imaging of Intracellular Ca2+ Handling and Nitric Oxide Production in Endothelial and Smooth Muscle Cells of an Isolated Rat Aorta at JoVE.com

Two-photon Imaging of Intracellular Ca2+ Handling and Nitric Oxide Production in Endothelial and Smooth Muscle Cells of an Isolated Rat Aorta

Vascular cell functiondepends on activity of intracellular messengers. Described here is an ex vivo two photon imaging method that allows the measurement of intracellular calcium and nitric oxide levels in response to physiological and pharmacological stimuli in individual endothelial and smooth muscle cells of an isolated aorta.

Two-photon Imaging of Intracellular Ca2+ Handling and Nitric Oxide Production in Endothelial and Smooth Muscle Cells of an Isolated Rat Aorta

Calcium is a very important regulator of many physiological processes in vascular tissues. Most endothelial and smooth muscle functions highly depend on ...

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11.2K Views.  Medical College of Wisconsin. Vascular cell functiondepends on activity of intracellular messengers. Described here is an ex vivo two photon imaging method that allows the measurement of intracellular calcium and nitric oxide levels in response to physiological and pharmacological stimuli in individual endothelial and smooth muscle cells of an isolated aorta. 