The Direct Effects of Heparin and Protamine on Canine Tracheal Smooth Muscle Tone

Abstract

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 2ϩ concentration ([Ca 2ϩ ] i ) and by measuring inward Ca 2ϩ currents (I Ca ) through voltage-dependent Ca 2ϩ channels.[Ca 2ϩ ] i was monitored by the 500-nm light emission ratio of preloaded Ca 2ϩ 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 heparinprotamine complex dose-dependently inhibited both carbachol-induced contraction of the muscle and increase in [Ca 2ϩ ] 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 2ϩ ] i . Protamine and heparin-protamine complex can decrease the agonist-induced increase in [Ca 2ϩ ] i by the inhibition of voltage-dependent Ca 2ϩ 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 2ϩ . These drugs can decrease the agonistinduced increase in intracellular Ca 2ϩ by the inhibition of voltage-dependent Ca 2ϩ channels in both the activated and inactivated states.

Glycosaminoglycans, Airways Inflammation and Bronchial Hyperresponsiveness

“…74,79 Such effects asthma in a small, subjectively assessed trial in 1960 are unlikely to be attributable to direct relaxant effects and was found to be ninety percent effective in proon smooth muscle as heparin has no effect on isolated viding relief of symptoms, when administered intraairway smooth muscle contractions elicited by musvenously. 61 carinic agonists, [80][81][82][83] although antigen-induced conMore recently, heparin delivered by inhalation was traction in airway smooth muscle from immunised found to prevent reduction in specific airway consheep is sensitive to heparin, 81 further supporting the ductance in subjects with exercise-induced asthma. [62][63][64] hypothesis that the acute bronchoprotective actions of this molecule are mediated through effects on mast In atopic asthmatics, a single inhaled dose of heparin …”

Editorial II

“…In contrast, it has been shown that both protamine and the heparin±protamine complex can inhibit canine tracheal smooth muscle contraction by decreasing [Ca 2+ ] i in vitro. 19 These agents decrease the agonist-induced increase in [Ca 2+ ] i by inhibition of VDCCs. 19…”