ROLES OF THE VOLTAGE-GATED K-1.5 AND KV-1.4, IN THE DEVELOPMENTAL-CHANGES OF K+ CURRENTS IN CULTURED NEONATAL RAT VENTRICULAR CELLS( CHANNEL SUBUNITS, KV)

To investigate the roles of voltage-gated K+ channel subunits. Kv 1.5 and Kv 1.4, in the developmental regulation of K+ currents, we determi ned the K+ channel activities and the distributions of K+ channel subu nits ill the same single cultured neonatal rat ventricular cells, usin g a whole-cell patch-clamp technique and an immunocytochemical analysi s of K+ channel proteins. In 5-day cultured cells, two types of 4-amin opyridine (4-AP)-sensitive and rapidly activating K+ currents, the tra nsient outward current (I-to) and the ultrarapid delayed rectifier (I- Kur), could be distinguished. A small proportion of 5-day cells expres sing sole I-Kur demonstrated an intense anti-Kv 1.5 antibody labeling with punctate distribution outlining the cells, while a weak staining was observed in the majority of 5-day cells expressing sole I-to. At d ay 15 of cell culture, only I-to was present with a lower level of the immunocytochemical expression of Kv 1.5 channel protein. Staining of the Kv 1.4 channel protein was qualitatively similar in the 5-day cell s expressing either I-to or I-Kur. However, anti-Kv 1.4 antibody did n ot label the 15-day cultured cells showing remarkably increased I-to d ensity. Our results strongly indicate that the Ky 1.5 channel expressi on may underlie the developmental regulation of I-Kur, while Kv 1.4 ch annel does not contribute to the postnatal increase in I-to.