The contribution of intermediate conductance calcium-dependent potassium channels to hypothalamic vasopressin neuronal excitability

Abstract

Vasopressin (VP) magnocellular neurosecretory neurons of the supraoptic nucleus (SON) in the hypothalamus 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. Hyperexcitability is caused in part by changes in intrinsic excitability mechanisms, including the slow afterhyperpolarization (sAHP), a phenomenon underlain by a calcium-dependent K+ current ( I sAHP). The sAHP is activated by Ca2+ and results in an efflux of K+ from the cell, hyperpolarizing it, and throttling firing. Importantly, we found that the sAHP is greatly inhibited in VP neurons from HF rats, contributing to increased neuronal excitability in this condition. While the features of the sAHP are well characterized, the identification of the channel underlying the I sAHP is unknown. Combining patch clamp electrophysiology and pharmacology in Wistar rats, we investigated Intermediate conductance Ca2+-dependent K+ (IK) channels as a potential candidate responsible for carrying the I sAHP. We generated and measured I sAHPs in voltage clamp via fixed steps of twenty spikes at twenty Hz and measured the the I sAHP as the resulting tail current at the end of the pulse. To account for rundown of the current over the recording period and for the pharmacological blocker’s slow mechanism of action, we measured I sAHPs every 60 seconds for at least 15 minutes. Bath application of TRAM-34 (2 μM) at 7 minutes, a specific IK channel blocker, failed to inhibit I sAHP peak amplitude or area (p > 0.05; n=36 SON neurons). We used biocytin-filled pipettes to identify neurons post hoc and run immunohistochemistry for oxytocin (OT) and VP to identify cell type within the SON. We found no significant difference in I sAHP amplitude or area between VP and OT cells under either control or TRAM-34 application. Taken together, our studies indicate that IK channels do not contribute to the I sAHP in SON neurosecretory neurons, despite robust IK expression in this region. Future studies will aim at identifying the role that IK channels play in SON, as well as targeting other potential K+ channel candidates for this NHLBI F32 HL158172 (MKK) NHLBI HL090948 (JES) NINDS NS094640 (JES) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.