LOCALIZATION OF THE KV1.5 K+ CHANNEL PROTEIN IN EXPLANTED CARDIAC TISSUE

The cloned Kv1.5 K+ channel displays similar kinetics and pharmacology to a delayed rectifier channel found in atrial myocytes. To determine whether the Kv1.5 isoform plays a role in the cardiac action potentia l, it is necessary to confirm the expression of this channel in cardia c myocytes. Using antibodies directed against two distinct channel epi topes, the Kv1.5 isoform was localized in human atrium and ventricle. Kv1.5 was highly localized at intercalated disk regions as determined by colocalization with connexin and N-cadherin specific antibodies. Wh ile both antichannel antibodies localized the Kv1.5 protein in cardiac myocytes, only the NH2-terminal antibodies stained vascular smooth mu scle. The selective staining of vasculature by this antiserum suggests that epitope accessibility, and perhaps channel structure, varies bet ween cardiac and vascular myocytes. Kv1.5 expression was localized les s in newborn tissue, with punctate antibody staining dispersed on the myocyte surface. This increasing organization with age was similar to that observed for connexin. Future work will address whether altered K + channel localization is associated with cardiac disease in addition to changing with development.