Y. Yamamoto et al., Endothelium-dependent hyperpolarization and intercellular electrical coupling in guinea-pig mesenteric arterioles, J PHYSL LON, 514(2), 1999, pp. 505-513
1. Using the conventional whole-cell clamp method, the electrical responses
of individual smooth muscle and endothelial cells to acetylcholine (ACh) w
ere observed in multicellular preparations where the two types of cells rem
ained in close apposition.
2. In both types of cells, ACh induced similar hyperpolarizing responses wh
ich, when recorded in current clamp mode, had two phases (an initial fast a
nd a second slower phase).
3. After Mocking gap junctions, including myoendothelial junctions, with 18
beta-glycyrrhetinic acid, ACh induced an outward current with two phases i
n voltage-clamped endothelial cells. The outward current appeared around -9
0 mV and increased linearly with the membrane depolarization.
4. In smooth muscle cells, ACh failed to induce a membrane current after ga
p junctions had been blocked with 18 beta-glycyrrhetinic acid. The inhibiti
on of ACh-induced response by 18 beta-glycyrrhetinic acid was observed usin
g either sharp or patch electrodes.
5. Nominally Ca2+-free solution reduced the initial phase and abolished the
second phase of ACh-induced responses of endothelial cells. Both phases we
re also reduced by charybdotoxin (CTX).
6. Our results indicate that in guinea-pig mesenteric arterioles, ACh hyper
polarizes endothelial cells by activating Ca2+-activated K+ channels which
are sensitive to CTX. On the other hand, hyperpolarizing responses detected
in smooth muscle cells seem to originate in endothelial cells and conduct
to the muscle layer via myoendothelial gap junctions.