Transmural nerve stimulation of blood vessels in vitro: a critical examination

Use of the method of transmural nerve stimulation depends on the assumption that stimulation parameters can be chosen to selectively and maximally activate nerves without stimulating vascular smooth muscle directly. When commercial stimulators are used with low impedance electrodes, it may not be possible to validate this assumption, due to the limited current output in this situation. To circumvent this limitation a coupling device which provides a very low source impedance to the electrodes is described. Using this device in experiments on preparations of rabbit ear artery, we have demonstrated that it is possible to selectively activate nerves, without stimulating smooth muscle directly. Adrenergic nerve activation was blocked with guanethidine, phentolamine or tetrodotoxin, while responses to direct smooth muscle activation persist in the presence of these drugs. Appropriate parameters for supramaximal nerve stimulation vary with the type of preparation and electrode arrangement. The possibility of variation with tissue and species is also discussed.