Abstract
The strong inward rectification of the channels composed of subunits from the Kir2 subfamily is mainly caused by voltage-dependent blockade of the outward currents by the intracellular polyamines, spermine and spermidine (Nichols & Lopatin, 1997). The mechanism of the polyamine blockade of the Kir2 channels is complicated, involving more than two blocked sites or states (Yang et al. 1995; Guo & Lu, 2000). Consequently, a simple model that can describe both the voltage- and polyamine concentration-dependences of outward current amplitudes had not yet been proposed. Recently, we studied the blockade of Kir2.1 currents by spermine and spermidine and showed that the macroscopic conductances are well described by the sum of the currents through two populations of Kir2.1 channels with different susceptibilities to the polyamine blockade (Ishihara & Ehara, 2004). This finding explains well the steady-state outward current amplitude of the cardiac strong inward rectifier K+ current, IK1, which plays a significant role in repolarizing the cardiac action potential. Since it has been shown that the Kir2.2 subunit co-assembles with the Kir2.1 subunit to form the IK1 channel in some animal species, in this study, we analyzed the polyamine blockade of the Kir2.2 channels expressed in HEK 293T cells. [Jpn J Physiol 55 Suppl:S128 (2005)]
