Genetic Mutations of K_Ca2.3 and K_Ca3.1 Channels Affect Ca2+ Sensitivity

Author

Razan Orfali, Chapman UniversityFollow

Date of Award

Spring 5-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Pharmaceutical Sciences

First Advisor

Miao Zhang, Ph.D., Chair

Second Advisor

Kamaljit Kaur, Ph.D.

Third Advisor

Meng Cui, Ph.D.

Fourth Advisor

Sun Yang, Ph.D.

Abstract

The Ca²⁺-activated potassium channels K_Ca channels are a unique family of potassium channels activated by intracellular calcium. K_Ca channels are critical for maintaining K⁺ homeostasis and modulate several physiological processes, from the firing properties of neurons to the control of the transmitter release. The Ca²⁺ sensitivity of these channels allows intracellular Ca²⁺ to regulate the electrical activity of the cell membrane. Increased Ca²⁺ sensitivity of K_Ca channels caused by gain of function mutations (GOF) in the KCNN genes results in a broad spectrum of human channelopathies, including Zimmermann- Laband syndrome (ZLS), idiopathic non-cirrhotic portal hypertension (INCPH), and hereditary xerocytosis (HX). The impact of dysfunctional K_Ca2.3/K_Ca3.1 channels on human health has not been well documented. In this dissertation, I used inside-out patch clamp recordings to measure the apparent Ca²⁺ sensitivity of K_Ca2.3 and K_Ca3.1 heterologously expressed in HEK293 cells. Wild-type K_Ca2.3 channels have a Ca²⁺ EC₅₀ value of ∼0.3 μM, while the apparent Ca²⁺ sensitivity of wild-type K_Ca3.1 channels is ∼0.27 μM. The equivalent mutations related to the ZLS and INCPH in the S₄₅A/S₄₅B helices increased the apparent Ca²⁺ sensitivity of both K_Ca2.3 & K_Ca3.1 channel subtypes. However, the equivalent mutations related to the HX in HA/HB helices of K_Ca2.3 and K_Ca3.1 affected their apparent Ca²⁺ sensitivity differently. AP14145 reduced the apparent Ca²⁺ sensitivity of the hypersensitive mutant K_Ca2.3 channels. The results of my Ph.D. project would suggest the potential therapeutic usefulness of negative gating modulators as a novel target in these channelopathy-causing mutations. At the same time would guide us to design more potent and subtype-selective positive modulators targeting these channels.

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Recommended Citation

Orfali, RS. Genetic Mutations of K_Ca2.3 and K_Ca3.1 Channels Affect Ca2+ Sensitivity. [dissertation]. Irvine, CA: Chapman University; 2023. https://doi.org/10.36837/chapman.000489