Fig 1.
Schematic illustration of the set-up performing electrical stimulation of the aorta.
To elicit aortic contractions, the aorta was directly stimulated with a 5s pulse train at different frequencies (pulse width, 2ms) at a 4 min inter-stimulus train using a constant voltage generator. Once two stable series of contractions were obtained at the same frequency, the aorta was exposed to different drugs by direct application into the thoracic cavity in 1ml increments. That is, an additional 1 ml of drug solution was added to the thoracic cavity. The volume of mineral oil and/or Tyrode's solution placed in the cavity was approximately 5–7 ml. This was followed by a series of stimulations over 5 s that were spread 4 min apart.
Fig 2.
Effect of varying stimulation voltage on magnitude of the contractile response of the aorta.
Voltage was varied from 0.25–7.5V, whereas frequency and pulse duration were kept constant at 5Hz and 2ms, respectively. (A) Representative tracing of electrically induced contractions of the aorta in response to varying voltage stimuli (two/voltage; bars) and peak parameters (a') of a 10V induced single contraction and (a") the mean ± SEM of 5 contractions per aorta in three animals (arrow; TR = rise time, TF = fall time, SlopeL = leading slope, W50% = half-width, AUC = area under the curve). (B) Graph showing the stimulus-response profile of aortic contractions in relationship to the percent change in amplitude elicited by 10V (n = 4).
Fig 3.
Spontaneous rhythmic contractions (pulse pressure) of the aorta correlated to ECG.
(A, B) Representative tracings of aortic contractions (upper panel) and ECG recording (lower panel) before (A) and after (B) bleeding the rat.
Fig 4.
Contractile activity of the in vivo aorta following different frequencies of electrical stimulation.
Stimulation was applied for 2 ms duration, 10V intensity over a 5s pulse train. (A-C) Representative recordings of phasic contractions in response to 1.7 Hz (A), 5 Hz (B) and 10 Hz (C) stimulation frequencies. [Note: the fast contractions superimposed on a tonic rise in pressure in C.]
Fig 5.
Tetrodotoxin (TTX) inhibits electrically evoked aortic contractions (n = 8).
(A) Rhythmic phasic contractions electrically induced by a 5s pulse train (1.7 Hz, 2 msec, 10 volts). Topical application (1 mL of 2 μM) of TTX reduced contraction amplitude after a 4-minute exposure (B), and, with continued exposure, contractions were eliminated 12 minutes later (C). (D) Graph showing progressive inhibition of electrically induced contractions of the aorta after initial application of TTX. * Significance p<0.05. [Note: The 12 min time point was not used in the analysis as there was complete inhibition of the electrically-induced contraction of the aorta in all the animals.]
Fig 6.
Suppression of electrically evoked aortic contractions by phentolamine.
(A) Rhythmic phasic contractions elicited in the aorta by a 5s pulse train (1.7 Hz, 2 msec, 10 volts), the amplitude of which was reduced by topical application of 1 mL of 1 mM phentolamine (B). (C) Graph illustrating the mean change in pressure from baseline induced by electrical stimulation of the aorta in the absence and presence of phentolamine (n = 4). * Significance p<0.05.