The direct effects of heparin and protamine on canine tracheal smooth muscle tone.

Heparin and protamine are used for cardiopulmonary bypass in cardiac surgery; however, the direct effects and mechanisms of these drugs on airway smooth muscle tone are still not fully known. We investigated the in vitro effects of these drugs on canine tracheal smooth muscle by measuring the muscle tension and intracellular Ca 2+ concentration ([Ca 2+ ] i ) and by measuring inward Ca 2+ currents (I Ca ) through voltage-dependent Ca 2+ channels. [Ca 2+ was monitored by the 500-nm light emission ratio of preloaded Ca 2+ indicator fura-2. Isometric tension was measured simultaneously. Whole-cell patch clamp recording techniques were used to investigate the effects of the drugs on I Ca in freshly dispersed smooth muscle cells. Heparin (0.12-120 U/mL), protamine (0.15-150 U/mL), or heparin-protamine complex (4:5 U/U) was introduced into a bath solution. Protamine and heparin-protamine complex dose-dependently inhibited both carbachol-induced contraction of the muscle and increase in [Ca 2+ ] i . These drugs also decreased the I Ca of the muscle cells and shifted the inactivation curve to a more negative potential. Heparin itself had a slight enhancing effect on carbachol-induced muscle contraction without changing [Ca 2+ ] i . Protamine and heparin-protamine complex can decrease the agonist-induced increase in [Ca 2+ ] i by the inhibition of voltage-dependent Ca 2+ channels both in the activated and inactivated states. Implications: Protamine and heparin-protamine complex inhibited carbachol-induced canine tracheal smooth muscle contraction by inhibiting the increase in intracellular concentration of free Ca 2+ . These drugs can decrease the agonist-induced increase in intracellular Ca 2+ by the inhibition of voltage-dependent Ca 2+ channels in both the activated and inactivated states.