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Isolated cells from rat portal vein smooth muscle in short-term primary culture were studied using patch-clamp technique (whole-cell configuration). In order to study a calcium-activated chloride current, the potassium currents were blocked by intracellular cesium diffusion. Without EGTA in the pipette solution, depolarizing voltage pulses from a holding potential of −70 mV to positive potentials activated an early inward and a late outward current. The latter persisted as a long-lasting inward tail current when the membrane was repolarized to −70 mV. The outward current measured at the end of the pulse and the tail current were blocked by extracellular cobalt, after replacement of external calcium with barium, after removal of external calcium, and when the calcium concentration of the pipette solution was less than 0.5 μM, suggesting that they were calcium-dependent. The tail current decay was voltage sensitive, becoming faster with hyperpolarization. The reversal potential of the calcium-activated current was near the equilibrium potential for chloride ions, and was shifted as predicted by the Nernst equation when the extracellular or intracellular chloride concentration was changed. The calcium-activated current was blocked by adding micromolar concentrations of niflumic acid or millimolar concentrations of DIDS. This effect of compounds known to interfere with chloride channels together with the data on the equilibrium potential for chloride ions indicated above suggested the existence of a calcium-activated chloride current in vascular smooth muscle cells. [ABSTRACT FROM AUTHOR]

The effects of noradrenaline (NA) were investigated on both fast and slow Ca currents in isolated vascular cells from rat portal vein in short-term primary culture using the whole-cell patch-clamp technique. NA (1 μM) stimulated the fast Ca current when the slow Ca current was inhibited either by application of a dihydropyridine derivative or by increasing the cytoplasmic Ca concentration. Noradrenaline and caffeine greatly reduced the slow Ca current. As this inhibitory effect is suppressed after depletion of the intracellular Ca store, we propose that reduction of the slow Ca current by noradrenaline is mediated by a Ca release from the sarcoplasmic reticulum. [ABSTRACT FROM AUTHOR]