Intercellular electrical communication between smooth muscle and endothelial cells was examined in guinea-pig mesenteric arterioles using the whole-cell patch-clamp method. The time course of the current required to impose a 10 mV voltage clamp step was used to determine the extent of electrical coupling between them. Currents recorded from both smooth muscle and endothelial cells relaxed in a multi-exponential manner, indicating the existence of electrical coupling between cells. 2. 18beta-Glycyrrhetinic acid, a gap junction blocker, quickly blocked electrical communication at 40 microM, while neither heptanol nor octanol did so at concentrations of up to 1 mM. 3. In the current clamp mode, repetitive spikes, induced by 10 mM Ba2+ solutions, could be recorded from both kinds of cells. After blocking gap junctions, spikes could only be recorded from the smooth muscle cell layer, indicating that they had been conducted through myoendothelial junctions. 4. In endothelial cells, acetylcholine (ACh, 3 microM) induced hyperpolarizing responses, which had two phases (an initial fast and a second slower phase) in the current clamp condition. This ACh response persisted in the presence of 18beta-glycyrrhetinic acid, although this compound seemed to make the membrane slightly leaky. 5. After blocking gap junctions, the membrane potential of a single cell in a multicellular preparation could be well clamped. Thus, 18beta-glycyrrhetinic acid may be useful in studying the function of both arteriolar smooth muscle and endothelial cells while they remain located within a multicellular preparation.
