Spatiotemporal analysis of spontaneous myogenic contractions in the urinary bladder of the rabbit: timing and patterns reflect reported electrophysiology

Abstract

The dynamics of propagating myogenic contractions in the wall of the resting ex vivo urinary bladder of the rabbit were characterized by spatiotemporal maps and related to cyclic variation in intravesical pressure (P). Patches of propagating contractions (PPCs) enlarged and involuted in near synchrony with peaks in P [mean 3.85 ± 0.3 cycles per minute (cpm)] and were preceded by regions of stretch. The maximum area of the bladder undergoing contraction (55.28 ± 2.65%) and the sizes of individual PPCs (42.61 ± 1.65 mm) coincided with the peak in P PPCs originated and propagated within temporary patch domains (TPDs) and comprised groups of nearly synchronous cyclic propagating individual contractions (PICs). The TPDs were located principally along the vertical axis of the anterior surface of the bladder. The sites of origin of PICs within PPCs were inconsistent, consecutive contractions often propagating in opposite directions along linear maps of strain rate. Similar patterns of movement occurred in areas of the anterior bladder wall that had been stripped of mucosa. P varied cyclically with area of contraction and with the indices of aggregation of PPCs, indicating that they grew by peripheral enlargement and collision without annihilation. The synchronization of PICs within PPCs was sometimes lost, uncoordinated PICs then occurring irregularly (between 4 and 20 cpm) having little effect on P We postulate that the formation and involution of PPCs within a TPD resulted from cyclic variation in excitation that increased the incidence and distance over which component PICs propagated.

Pharmacological modulation of the spatiotemporal disposition of micromotions in the intact resting urinary bladder of the rabbit; their pattern is under both myogenic and autonomic control

“…Hence the frequencies of regular ‘burst’ patterns of multiple action potentials (mean 4.2 ± 2.2 cyles per min [cpm]) reported by Hashitani and Brading and Hashitani et al. are similar to those of coordinated PPCs we observed in the intact pig bladder (3 cpm) and in the rabbit bladder (3.85 ± 0.3 cpm) , whilst the frequency range in patterns of randomly spaced single action potentials (14.5 ± 6.2 cpm) is similar to that of isolated patches of myogenic contraction (PICs; 4–20 cpm) . To date little is known about the way in which autonomic neurotransmitters, and other agents that interfere with tonal smooth muscle contraction at a cellular level, influence the development of these various patterns of contraction in the intact bladder and the consequent adjustment of tone and compliance.…”

“…The bladder was mounted in the same manner as has been described previously . Briefly, it was first cannulated with a curved metal cannula (2 mm outer diameter (OD)), which was secured with a ligature 5 mm distal to the bladder neck.…”

“…linear plots of the variation in strain rate ( x axis) at all points along a line of interest (LOI) over time ( y axis), were also generated from the video. Analyses were conducted over two LOIs that were positioned vertically so as to traverse the right‐ and the left‐hand sides of the bladder, as this is the reported principal direction of propagation . The vertical speeds and directions of propagation of a contraction, or group of contractions, could be directly determined from these maps as it was possible to measure the angle of the contraction stripe to the horizontal axis.…”

“…Recent work has shown that the spatiotemporal organization of micromotions is more complex than was originally described and not always synchronous with oscillations in intravesical pressure . Hence in the rabbit bladder, there are periods when regular, vertically propagating, relatively prolonged, synchronized contractions of large areas of the bladder wall, i.e.…”

“…These periods are interspersed with periods when shorter‐lived, small, localized contractions, i.e. propagating individual contractions (PICs), predominate, which have relatively little effect on intravesical pressure . Further, the temporal characteristics of these two patterns are similar to those of electrophysiological events in tissue from the bladder wall.…”