Biomolecular Basis for Cold-Induced Contraction of Coronary Arteries in the Newborn Lamb: Implication in Myocardial Dysfunction after Hypothermic Cardiopulmonary Bypass ♦ 98

Introduction: Despite improved overall outcome after open heart surgery, early myocardial dysfunction remains a problem in the infant and the neonate in the post hypothermic cardiopulmonary bypass recovery period. We hypothesize that a vasoconstriction of the conductance coronary arteries (CA) occurs when exposed to cold, and that this cold induced contraction involves protein tyrosine kinase (PTK)-/protein tyrosine phosphatase (PTP)-dependent signal transduction pathways. Methods: Newborn lamb 3-mm CA ring segments (1mm diameter) were studied in tissue bath (Krebs buffer, 21%O₂, 5%CO₂) for isometric contraction during a 2-hour exposure to hypothermia (7° & 17°C). In parallel, 8-mm CA ring segments were evaluated for changes in protein tyrosine phosphorylation using standard electrophoretic and immunoblotting techniques (monoclonal anti-phosphotyrosine antibody & chemiluminescence detection). Na-orthovanadate (SOV), a potent PTP inhibitor, and genestein (Gen), a non selective PTK inhibitor, were used separately and in combination to evaluate their effect on contractile behavior and tyrosine phosphorylation of CA during cooling (7° or 17°C) vs. 37°C. Results: Tissue bath cooling to 17°C resulted in sustained contraction (25% KCl, n=4), reversible upon rewarming. CA segments subjected to 7°C cooling demonstrated a transitory contraction at≈17°C, more prominent during rewarming (5-15% KCl). Cold-induced contraction was abolished in the presence of Gen and significantly enhanced(2-fold) in the presence of SOV, the latter being partially inhibited in the presence of Gen. There was increased tyrosine phosphorylation of 25, 30-33 and 100-110 kDa proteins detected at 17°C compared to 37°C (n=4), similarly enhanced by SOV and abolished by Gen.

Conclusion: These findings support our hypothesis linking cold-induced contraction of coronary arteries to PTK/PTP-dependent machinery. We speculate that cold-induced protein tyrosine phosphorylation may provide a pathophysiological basis for CA dysfunction and its ramification on post hypothermic cardiopulmonary bypass myocardial recovery.