Hypoxic vasorelaxation inhibition by organ culture correlates with loss of Kv channels but not Ca2+ channels

We (Thorne GD, Shimizu S, and Paul RJ. Am J Physiol Cell Physiol 281: C24-C32, 2001) have recently shown that organ culture for 24 h specifically inhibits relaxation to acute hypoxia (95% N-2-5% CO2) in the porcine coronary artery. Here we show similar results in the porcine carotid artery and the rat and mouse aorta. In the coronary artery, part of the inability to relax to hypoxia after organ culture is associated with a concomitant loss in ability to reduce intracellular Ca2+ concentration ([Ca2+](i)) during hypoxia (Thorne GD, Shimizu S, and Paul RJ. Am J Physiol Cell Physiol 281: C24-C32, 2001). To elucidate the mechanisms responsible for the loss of relaxation to hypoxia, we investigated changes in K+ and Ca2+ channel activity and gene expression that play key roles in [Ca2+](i) regulation in vascular smooth muscle (VSM). Reduced mRNA expression of O-2-sensitive K+ channels (Kv1.5 and Kv2.1) was shown by reverse transcriptase-polymerase chain reaction in the rat aorta. In contrast, no change in other expressed voltage-gated K+ channels (Kv1.2 and Kv1.3) or Ca2+ channel subtypes was found. Modified K+ channel expression is supported by functional evidence indicating a reduced response to general K+ channel activation, by pinacidil, and to specific voltage-dependent K+ (Kv) channel blockade by 4-aminopyridine. In conclusion, organ culture decreases expression of specific Kv channels. These changes are consistent with altered mechanisms of VSM contractility that may be involved in Ca2+-dependent pathways of hypoxia-induced vasodilation.