Effects of noradrenaline and heparin on outward current in single smooth muscle cells of the guinea-pig vas deferens.

A transient outward current (Ito) was elicited by depolarization in single smooth muscle cells isolated from guinea-pig vas deferens under whole-cell voltage-clamp conditions. The peak amplitude of Ito was markedly decreased by over 80% within 10 s after application of 10 microM noradrenaline. When the pipette solution contained low molecular weight heparin (0.3-5 mg/ml), the inhibitory effect of 10 microM noradrenaline on Ito was apparently reduced. Our results strongly suggest that the noradrenaline-induced suppression of Ito is an event subsequent to Ca2+ release and depletion of available Ca2+ stored in the sarcoplasmic reticulum (SR) by myo-inositol 1,4,5-trisphosphate (InsP3), an event which is blocked by low molecular weight heparin.