Voltage-gated K+ channel, Kv4.2, localizes predominantly to the transverse-axial tubular system of the rat myocyte

Kv4.2 subunit, a member of K+ channel gene family, is considered to play a major role in the formation of depolarization-activated transient outward K + current channels in the mammalian heart, We investigated the subcellular localization of Kv4.2 subunit in the rat heart by immunofluorescence and im munoelectron microscopy. In atrial cells, Kv4.2 immunofluorescent staining was intensely observed in the peripheral sarcolemma and the intercalated di sks, but seldom found in transverse tubules, which are rare or absent in at rial cells. In ventricular cells, the labeling of Kv4.2 immunofluorescent s taining was found throughout the entire cell membrane, and the staining was stronger in the transverse-axial tubular system than in the peripheral sar colemma, Correlative immunoconfocal and immunoelectron microscopy using Flu oroNanogold confirmed that Kv4.2 distributed in the transverse-axial tubula r system including the longitudinally oriented axial tubules, Immunogold el ectron microscopy of ultrathin cryosections revealed that Kv4.2 was distrib uted on the plasma membranes of the T-tubules, The extensive distribution o f Kv4.2 on the entire cell membrane of myocytes would provide rat myocardia l cells with a large capability for the transport of K+ ions through the ch annels in the repolarization phase. (C) 2000 Academic Press.