Endothelium-dependent hyperpolarization and intercellular electrical coupling in guinea-pig mesenteric arterioles

The mechanisms by which endothelial cells influence vascular tone remain partially unclear. It is known that endothelial cells can release factors that modulate smooth muscle activity. However, the direct electrical communication between endothelial and smooth muscle cells is less well understood. Some studies suggest that gap junctions may facilitate this communication. Yet, the precise role of these junctions in acetylcholine (ACh)-induced responses is not fully established. The contribution of calcium-activated potassium channels in this process is also uncertain. This uncertainty drives the need for detailed electrophysiological studies. Researchers aim to clarify the sequence of events following ACh stimulation. Understanding these interactions may improve models of vascular reactivity. This paper addresses a specific gap in the current knowledge of endothelial signaling.

This study aimed to investigate the electrical responses of endothelial and smooth muscle cells to acetylcholine in guinea-pig mesenteric arterioles. The researchers wanted to determine whether these responses are endothelium-dependent and whether they involve intercellular communication. They focused on the role of gap junctions in transmitting signals between cell types. The study also examined the contribution of calcium and potassium channels to the observed responses. By using whole-cell clamp techniques, they could isolate and measure the effects of specific inhibitors. The goal was to distinguish between direct and indirect effects of ACh on smooth muscle cells. The study aimed to clarify the sequence of events following ACh application. This approach allows for a detailed understanding of endothelial signaling mechanisms.

The researchers used the whole-cell clamp technique to measure electrical responses in isolated smooth muscle and endothelial cells. They maintained close apposition between the two cell types in multicellular preparations. Acetylcholine was applied to induce hyperpolarizing responses in both cell types. Gap junctions were blocked using 18beta-glycyrrhetinic acid to assess their role in signal transmission. Voltage-clamp recordings were used to measure outward currents in endothelial cells. Current-clamp mode was used to observe the two-phase hyperpolarizing response. The effects of calcium-free solutions and charybdotoxin were tested to evaluate ion channel involvement. The study combined pharmacological and electrophysiological approaches to dissect the signaling pathway.

Acetylcholine induced similar hyperpolarizing responses in both endothelial and smooth muscle cells. These responses had two distinct phases when recorded in current clamp mode. Blocking gap junctions with 18beta-glycyrrhetinic acid altered the response in endothelial cells. In voltage-clamped endothelial cells, ACh induced an outward current with two phases. The outward current appeared around -90 mV and increased with depolarization. In smooth muscle cells, ACh failed to induce a membrane current after gap junction block. Charybdotoxin reduced both phases of the ACh-induced response in endothelial cells. Nominally Ca2+-free solution reduced the initial phase and abolished the second phase.

The study suggests that ACh hyperpolarizes endothelial cells by activating Ca2+-activated K+ channels sensitive to CTX. The hyperpolarizing responses in smooth muscle cells appear to originate in endothelial cells. These responses are transmitted to the muscle layer via myoendothelial gap junctions. The findings support the role of gap junctions in endothelial-smooth muscle communication. The results indicate that calcium and potassium channels are essential for the observed responses. The study clarifies the sequence of events following ACh application. The data align with the hypothesis of endothelium-dependent hyperpolarization. The conclusions are based on the observed effects of specific inhibitors and ion channel blockers.