Roles of the voltage-gated K+ channel subunits, Kv 1.5 and Kv 1.4, in the developmental changes of K+ currents in cultured neonatal rat ventricular cells

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 determined the K+ channel activities and the distributions of K+ channel subunits ill the same single cultured neonatal rat ventricular cells, using a whole-cell patch-clamp technique and an immunocytochemical analysis of K+ channel proteins. In 5-day cultured cells, two types of 4-aminopyridine (4-AP)-sensitive and rapidly activating K+ currents, the transient outward current (I-to) and the ultrarapid delayed rectifier (I-Kur), could be distinguished. A small proportion of 5-day cells expressing 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 day 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 cells expressing either I-to or I-Kur. However, anti-Kv 1.4 antibody did not label the 15-day cultured cells showing remarkably increased I-to density. Our results strongly indicate that the Ky 1.5 channel expression may underlie the developmental regulation of I-Kur, while Kv 1.4 channel does not contribute to the postnatal increase in I-to.