Effect of Cd²⁺ on Kv4.2 and Kv1.4 Expressed in <i>Xenopus</i> Oocytes and on the Transient Outward Currents in Rat and Rabbit Ventricular Myocytes

Abstract

The aim of the present study was to compare the biophysical properties and Cd²⁺ sensitivity of Kv4.2 and Kv1.4 in Xenopus oocytes with those of native transient outward potassium currents in rat and rabbit ventricular myocytes. In Xenopus oocytes, Kv4.2 inactivated at hyperpolarized voltages (V_½^inact = –58.4 ± 0.96 mV, n = 12) and recovered from inactivation rapidly (time constant = 224 ± 23 ms, n = 3). Cd²⁺ induced large (approx. 30 mV with 500 μM Cd²⁺), concentration-dependent rightward shifts in Kv4.2 steady-state activation and inactivation. Kv1.4 inactivated over more depolarized voltages than Kv4.2 (V_½^inact = –49.3 ± 1.4 mV, n = 12). Recovery from inactivation of Kv1.4 was dominated by a large slow component (time constant = 9,038 ± 1,178 ms, n = 4). Cd²⁺ exerted only modest effects on Kv1.4 gating, with 500 μM Cd²⁺ shifting the voltage dependence of steady-state activation and inactivation by approximately 12 mV.We show that the biophysical properties and Cd²⁺ sensitivity of rat ventricular I_to resemble those of heterologously expressed Kv4.2. These findings support previous suggestions that Kv4.2 is an important molecular component of I_to in adult rat heart. In addition, our findings show that I_to in rabbit ventricular myocytes and Kv1.4-based currents in Xenopus oocytes share similar biophysical properties and sensitivity to Cd²⁺, suggesting that Kv1.4 may underlie I_to in rabbit ventricle. However, a number of discrepancies exist between the properties of native currents and their putative molecular counterparts, suggesting that additional proteins and/or modulatory factors may also play a role in determining the biophysical and pharmacological properties of these native currents.

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,ItoK+currents, and [Ca2+]itransients

“…Similar correlations between Kv4.x genes and I to have been documented in humans (17,28,52) and other animal species (16,17,21,25,58,59). By contrast, no regional differences in Kv4.3 expression were observed.…”

“…mRNA and protein expression of Kv1.4 was higher in the RVW versus SEP. The significance of the current produced by these channels remains unclear, but recent studies (25,39,(58)(59)(60) have suggested that in rodents this channel encodes for the slow component of I to (see below). If correct, the relative contribution of Kv1.4 channels to the total amplitude of I to recorded at low rates of stimulation is relatively small in both the RVW and SEP even after MI.…”

“…The concentration of RNA was measured spectrophotometrically and confirmed by agarose gel electrophoresis. RNase protection assays were performed as previously described (30,59).…”

Postnatal development of A-type and Kv1- and Kv2-mediated potassium channel currents in neocortical pyramidal neurons

“…All of the data thus far were obtained in the presence of 100 M Cd 2ϩ to block Ca 2ϩ currents and Ca 2ϩ -dependent currents. We previously reported negligible effects of 0.1 Cd 2ϩ on the persistent components of the K ϩ current in these cells (Guan et al 2007b); however, Cd 2ϩ has been shown to shift the voltage dependence and kinetics of Kv currents (especially Kv4 mediated; Davidson and Kehl 1995;Follmer et al 1992;Guan et al 2007b;Wickenden et al 1999). We tested the effects of 100 M Cd 2ϩ on A-type currents in five cells with a recovery from inactivation protocol (see below) and found that Cd 2ϩ significantly reduced the peak A-type current at ϩ10 mV (1,589 Ϯ 371 vs. 467 Ϯ 86 pA) and slowed the TTP (3.2 Ϯ 0.3 vs. 7.8 Ϯ 0.5 ms).…”

“…For experiments designed to study the rapidly activating and inactivating A-type current, we used an external recording solution without Cd 2ϩ present because Cd 2ϩ shifts the voltage dependence of both activation and inactivation of Kv4 channels to more depolarized potentials and slows their kinetics (Guan et al 2007b;Song et al 1998;Wickenden et al 1999). Our initial method for isolating the A-type current was via a voltage protocol.…”