Effects of Cd2+ on transient outward and delayed rectifier potassium currents in acutely isolated rat hippocampal CA1 neurons

Cardiac Toxicity of Cadmium Involves Complex Interactions Among Multiple Ion Currents in Rainbow Trout (Oncorhynchus mykiss) Ventricular Myocytes

Cadmium (Cd²⁺ ) is cardiotoxic to fish, but its effect on the electrical excitability of cardiac myocytes is largely unknown. To this end, we used the whole-cell patch-clamp method to investigate the effects of Cd²⁺ on ventricular action potentials (APs) and major ion currents in rainbow trout (Oncorhynchus mykiss) ventricular myocytes. Trout were acclimated to +4 °C, and APs were measured at the acclimated temperature and elevated temperature (+18 °C). Cd²⁺ (10, 20, and 100 µM) altered the shape of the ventricular AP in a complex manner. The early plateau fell to less positive membrane voltages, and the total duration of AP prolonged. These effects were obvious at both +4 °C and +18 °C. The depression of the early plateau is due to the strong Cd²⁺ -induced inhibition of the L-type calcium (Ca²⁺ ) current (I_CaL ), whereas the prolongation of the AP is an indirect consequence of the I_CaL inhibition: at low voltages of the early plateau, the delayed rectifier potassium (K⁺ ) current (I_Kr ) remains small, delaying repolarization of AP. Cd²⁺ reduced the density and slowed the kinetics of the Na⁺ current (I_Na ) but left the inward rectifier K⁺ current (I_K1 ) intact. These altered cellular and molecular functions can explain several Cd²⁺ -induced changes in impulse conduction of the fish heart, for example, slowed propagation of the AP in atrial and ventricular myocardia (inhibition of I_Na ), delayed relaxation of the ventricle (prolongation of ventricular AP duration), bradycardia, and atrioventricular block (inhibition of I_CaL ). These findings indicate that the cardiotoxicity of Cd²⁺ in fish involves multiple ion currents that are directly and indirectly altered by Cd²⁺ . Through these mechanisms, Cd²⁺ may trigger cardiac arrhythmias and impair myocardial contraction. Elevated temperature (+18 °C) slightly increases Cd²⁺ toxicity in trout ventricular myocytes. Environ Toxicol Chem 2021;40:2874-2885. © 2021 SETAC.

The electrophysiological effects of cadmium on Retzius nerve cells of the leech Haemopis sanguisuga

Cadmium is considered one of the most toxic heavy metals which can cause cytotoxicity in multiple organs including the brain. Despite many studies over the past decades, the cellular and molecular mechanisms underlying its neurotoxicity remain unclear. The present study was designed to examine the acute effects of cadmium chloride (CdCl₂) on the electrical activity of the Retzius nerve cells of leech Haemopis sanguisuga using electrophysiological techniques. CdCl₂, in concentrations of 10-100 μM, produced a dose- and time-dependent depolarization of Retzius neurons, paralleled by an increase in firing frequency and action potential duration. To examine potential mechanisms, we studied the effects of cadmium on the outward potassium current upon depolarization using a point microelectrode voltage-clamp technique. Reduction of the fast, and partial inhibition of the slow outward current were observed after adding 50 and 100 μM CdCl₂ in the external fluid. The present results support the view that the effect of cadmium on the outward potassium channel may be a potential contributing mechanism for cadmium-induced neurotoxic damage. The proposed mechanism of cadmium action on the electrical properties of leech Retzius neurons might have broader significance concerning not only the leeches but vertebrate brains as well.

Genistein inhibition of OGD-induced brain neuron death correlates with its modulation of apoptosis, voltage-gated potassium and sodium currents and glutamate signal pathway

In the present study, we established an in vitro model of hypoxic-ischemia via exposing primary neurons of newborn rats to oxygen-glucose deprivation (OGD) and observing the effects of genistein, a soybean isoflavone, on hypoxic-ischemic neuron viability, apoptosis, voltage-activated potassium (Kv) and sodium (Nav) currents, and glutamate receptor subunits. The results indicated that OGD exposure reduced the viability and increased the apoptosis of brain neurons. Meanwhile, OGD exposure caused changes in the current-voltage curves and current amplitude values of voltage-activated potassium and sodium currents; OGD exposure also decreased GluR2 expression and increased NR2 expression. However, genistein at least partially reversed the effects caused by OGD. The results suggest that hypoxic-ischemia-caused neuronal apoptosis/death is related to an increase in K(+) efflux, a decrease in Na(+) influx, a down-regulation of GluR2, and an up-regulation of NR2. Genistein may exert some neuroprotective effects via the modulation of Kv and Nav currents and the glutamate signal pathway, mediated by GluR2 and NR2.

Cadmium impairs ion homeostasis by altering K+ and Ca2+ channel activities in rice root hair cells

Cadmium (Cd2+) interferes with the uptake, transport and utilization of several macro- and micronutrients, which accounts, at least in part, for Cd2+ toxicity in plants. However, the mechanisms underlying Cd2+ interference of ionic homeostasis is not understood. Using biophysical techniques including membrane potential measurements, scanning ion-selective electrode technique for non-invasive ion flux assays and patch clamp, we monitored the effect of Cd2+ on calcium (Ca2+) and potassium (K+) transport in root hair cells of rice. Our results showed that K+ and Ca2+ contents in both roots and shoots were significantly reduced when treated with exogenous Cd2+. Further studies revealed that three cellular processes may be affected by Cd2+, leading to changes in ionic homeostasis. First, Cd2+ -induced depolarization of the membrane potential was observed in root hair cells, attenuating the driving force for cation uptake. Second, the inward conductance of Ca2+ and K+ was partially blocked by Cd2+, decreasing uptake of K+ and Ca2+ . Third, the outward K+ conductance was Cd2+ -inducible, decreasing the net content of K+ in roots. These results provide direct evidence that Cd2+ impairs uptake of Ca2+ and K+, thereby disturbing ion homeostasis in plants.