Conducted vasodilation caused by the micropipette application of methacholine was quantified to determine if there was a limit to the response that can be transmitted by an arteriole. Arterioles in the cheek pouch of anesthetized hamsters were studied using videomicroscopy. Methacholine was either ejected onto the surface of an arteriole or injected into the lumen with a pneumatic ejector. Protocol I (n=I9): Methacholine (10-7-10-3M) was injected into the lumen of an arteriole for 3 sec. and dilatory responses were measured 500 μm upstream from the site of injection, The conducted response increased with drug concentration to a maximum response of 7±0.8 um (at 10-6M) and then did not increase any further. Protocol II: Methacholine was simultaneously applied for 5 sec, from up to four pipettes spaced 100 urn apart. Applying 10-5 methacholine (n=6) showed an increased response with each additional pipette up to a maximum dilation of 5.2±1.1 um when all four were used. This maximum was not further increased by using 10-4 methacholine (n=7). The conducted dilations were not significantly different from 5.3±2.2 μm regardless of the number of pipettes used. Protocol III (n=8):Methacholine was continuously applied to an arterioie for 40 sec. The conducted response maximized by 10 sec. and was 4.9±0.5 μm. Protocol IV (n=6): Methacholine was applied for 5 sec. onto two adjacent arteriole branches having a common point 500 μm upstream. The conducted dilation seen when MCh was simultaneously applied (6.1±1,2 μm) was almost twice that seen when each branch was stimulated independently (3.7±.8 μm). In protocols I - III there was a maximum conducted response that could be transmitted from a single arteriole, and the magnitude was similar for all protocols. In contrast, when similar applications were made onto adjacent arterioles, the responses were additive. These data indicate mat there is a maximum conducted signal that can be transmitted by an arteriole and this may be due to a self-limiting feature of communication through gap junctions.
|Original language||English (US)|
|State||Published - Dec 1 1996|
ASJC Scopus subject areas
- Molecular Biology