Blocking intermediate conductance Ca2+-dependent K+ channels with TRAM-34 failed to inhibit the slow afterhyperpolarization in vasopressin or oxytocin neurons of the supraoptic nucleus.
Intermediate conductance Ca2+-dependent K+ channels do not significantly contribute to the slow afterhyperpolarization in oxytocin and vasopressin hypothalamic magnocellular neurons, despite their functional presence.
Abstract Vasopressin (VP) magnocellular neurosecretory neurons of the hypothalamic supraoptic nucleus (SON) are critical regulators of renal water retention and vascular tone. VP neurons undergo detrimental plastic changes in cardiovascular diseases such as heart failure (HF), resulting in hyperexcitability and thus altered fluid/electrolyte balance. A major intrinsic mechanism that regulates the firing activity of VP neurons is the slow afterhyperpolarization (sAHP), a phenomenon underlain by a calcium‐dependent K + current ( I sAHP ). The sAHP is activated by Ca 2+ and results in an efflux of K + from the cell, hyperpolarizing it and throttling firing. Importantly, we previously reported that a blunted sAHP contributes to hyperexcitability of VP neurons in heart failure rats. While the features of the sAHP are well characterized, the identity of the channel underlying the I sAHP remains unknown. Combining patch clamp electrophysiology, pharmacology and immunohistochemistry in Wistar rats, we investigated Intermediate conductance Ca 2+ ‐dependent K + (IK) channels as a potential candidate responsible for carrying the I sAHP . We generated and measured the I sAHP in voltage clamp via 20 Hz trains of 20 square voltage pulses (from −50 to +10) once per minute. After 4 min of baseline recording, we bath applied TRAM‐34 (1 μM), a specific IK channel blocker. Blocking IK with TRAM‐34 failed to inhibit I sAHP peak amplitude, amplitude at 1 s after stimulus end, or area. Post hoc immunohistochemistry was performed to identify the phenotype of the recorded cell. We observed no inhibitory effect of TRAM‐34 on the I sAHP in either VP or OT neurons. We also saw no inhibition of I sAHP (voltage clamp) or sAHP (current clamp) in slices preincubated in TRAM‐34 for at least 1 h prior to recording. Conversely, we found that TRAM‐34 inhibited isolated whole cell K + currents, supporting the presence of functional, TRAM‐34‐sensitive IK channels in SON neurons. Taken together, our results indicate that despite the expression of IK in SON neurons and astrocytes, we observed no evidence of a significant contribution to the sAHP in either OT or VP SON neurons. Future studies will be needed to determine other potential K + channel candidates contributing to the sAHP in SON neurons.
Shook et al. (Thu,) conducted a other in Healthy (Wistar rats). TRAM-34 vs. Baseline was evaluated on Inhibition of IsAHP peak amplitude, amplitude at 1 s after stimulus end, or area. Blocking intermediate conductance Ca2+-dependent K+ channels with TRAM-34 failed to inhibit the slow afterhyperpolarization in vasopressin or oxytocin neurons of the supraoptic nucleus.