Opposing effects of noradrenaline on the two classes of voltage-dependent calcium channels of single vascular smooth muscle cells in short-term primary culture.

The effects of noradrenaline (NA) were investigated on both fast and slow Ca2+ currents in isolated vascular cells from rat portal vein in short-term primary culture using the whole-cell patch-clamp technique. NA (1 microM) stimulated the fast Ca2+ current when the slow Ca2+ current was inhibited either by application of a dihydropyridine derivative or by increasing the cytoplasmic Ca2+ concentration. Noradrenaline and caffeine greatly reduced the slow Ca2+ current. As this inhibitory effect is suppressed after depletion of the intracellular Ca2+ store, we propose that reduction of the slow Ca2+ current by noradrenaline is mediated by a Ca2+ release from the sarcoplasmic reticulum.