Concentration Response Curves

Most of the results obtained from wire myography are from looking at the response of the vessel to agonists or antagonists that have been added to the bath. This is usually done in the form of a CCRC, also known as a dose-response curve. In order to achieve receptor saturation, large ranges of concentrations are required, so CCRC are usually logarithmic. This typically produces a curve of sigmoidal shape, with the segment between 20 and 80% of the maximal response being approximately linear.

When performing a vasoconstrictor CCRC, a suitable time interval should be left between each dose until contraction begins, at which point each subsequent dose should be added when contraction has peaked. Once the higher concentrations are reached, desensitization, or tachyphylaxis, may occur. This is a reduced response to the agonist when the agonist is continually present at the receptor (14) (see Note 8).

In vasodilator curves, each vessel is first contracted to 80% of its maximum using a suitable agonist, e.g., NE. Once the vessel starts to relax, subsequent doses of agonist should be added when the response has leveled off. In vasodilator curves a common problem is spontaneous relaxation, where the vessel will fail to maintain contraction and relax to baseline either before or during the CCRC. If this happens, the vessel should be washed with fresh PSS and allowed to rest before a further attempt is made.

When designing an experimental protocol for wire myography, care should be taken with the order in which agonists are used. Certain agonists are irreversible and so cannot be washed out; these should always be used last.

It may be helpful to denude the endothelium of blood vessels when looking at endothelium-dependent vascular responses. This can be done in either a mechanical manner using a hair and rubbing it along the endothelium, or by infusing the vessel with antibody and complement (15). If removing the endot-helium by mechanical means, care should be taken to avoid damaging the vascular smooth muscle cells.

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