Regulation of excitability of smooth muscle by endothelium in cerebral arterioles -Intercellular humoral and electrical signal transduction-

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In the present research project, I attended to investigate regulation of smooth muscle cells (SMCs) by endothelium (EC) via cell-to-dell humoral and electrical communication, using arterioles dissected from the rat cerebral pial membrane. 1. By means of the perforated whole-cell patch-clamp technique, a hyperpolarizing voltage step applied to SMC in voltage-clamp mode elicited the inward current through the SMC membrane as well as the outward current through EC membrane (gap-junctional current), which was attenuated by α-glycyrrhetinic acid (α-GA). This result suggests the existence of electrical coupling between SMC and EC. 2. To investigate the role of humoral factors, I examined the effect of bradykinin on endothelin-1 (ET-1)-evoked oscillatory Ca2+-activated Cl- currents (I_<Cl(Ca)>) under the condition where junctional current was abolished by α-GA. As a result, bradykinin was shown to release nitric oxide to an extracellular space, and to inhibit an ET-1-evoked I_<Cl(Ca)> in smooth muscle cells. 3. Gap junction was demonstrated to exist between adjacent SMCs. The junctional current declined time-dependently. This phenomenon was voltage-dependent, and symmetrical for the positive and negative junctional voltages. On the other hand, the junctional current between SMC and EC exerted asymmetrical voltage-dependency. Gap-conductance could be estimated according to the macroscopic current measured, series resistance created by the electrodes, and assumption that gap-resistance among the surrounded cells should be connected in parallel. Single-channel conductance could also be calculated under the condition where a gap-junction inhibitor was performed at a modest concentration. All of these techniques are likely to enable to analyze various types of communication between cells of microvasculature with intact structure.