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pubmed:abstractText |
1. The effects of endothelin were studied, in vitro, on neurones contained in the rabbit vesical pelvic ganglion by use of intracellular and single-electrode voltage clamp techniques under conditions where sodium and potassium channels were blocked. 2. In the current-clamp experiments, endothelin (1 microM) caused a depolarization followed by a hyperpolarization of the membrane potential. In the voltage-clamp experiments, endothelin (0.01-1 microM) caused an inward current followed by an outward current in a concentration-dependent manner. 3. Membrane conductance was increased during the endothelin-induced depolarization and inward current. Membrane conductance was decreased during the endothelin-induced hyperpolarization and outward current. 4. The endothelin-induced inward and outward currents were not altered by lowering external sodium concentration or raising external potassium concentration. 5. The endothelin-induced inward current was depressed (mean 72%) in a Krebs solution containing nominally zero calcium and high magnesium. These results suggest that a predominent component of the endothelin-induced inward current is mediated by calcium ions. 6. The calcium-insensitive component of the inward current was abolished by a chloride channel blocker, 4-acetamide-4'-isothiocyanostilbene-2,2'-disulphonic acid. The mean reversal potential for the calcium-insensitive component of the inward current was -18 mV. This value is near the equilibrium potential for chloride. Thus, it is presumed that the calcium-insensitive component of the inward current is carried by chloride ions. 7. Endothelin caused an initial depression followed by a long lasting facilitation of both rapidly and slowly decaying components of high-threshold calcium channel currents (N- and L-type). 8. In summary, the data show that for neurones in the vesical pelvic ganglia, endothelin causes membrane depolarization and activates an inward current. The ionic mechanisms involve receptor-operated calcium and chloride currents. Also, endothelin causes an initial depression followed by a long-lasting facilitation of the voltage-dependent calcium current.
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