CaV1.2 and CaV1.3 channel hyperactivation in mouse islet β cells exposed to type 1 diabetic serum

Abstract

The voltage-gated Ca(2+) (CaV) channel acts as a key player in β cell physiology and pathophysiology. β cell CaV channels undergo hyperactivation subsequent to exposure to type 1 diabetic (T1D) serum resulting in increased cytosolic free Ca(2+) concentration and thereby Ca(2+)-triggered β cell apoptosis. The present study was aimed at revealing the subtypes of CaV1 channels hyperactivated by T1D serum as well as the biophysical mechanisms responsible for T1D serum-induced hyperactivation of β cell CaV1 channels. Patch-clamp recordings and single-cell RT-PCR analysis were performed in pancreatic β cells from CaV1 channel knockout and corresponding control mice. We now show that functional CaV1.3 channels are expressed in a subgroup of islet β cells from CaV1.2 knockout mice (CaV1.2(-/-)). T1D serum enhanced whole-cell CaV currents in islet β cells from CaV1.3 knockout mice (CaV1.3(-/-)). T1D serum increased the open probability and number of functional unitary CaV1 channels in CaV1.2(-/-) and CaV1.3(-/-) β cells. These data demonstrate that T1D serum hyperactivates both CaV1.2 and CaV1.3 channels by increasing their conductivity and number. These findings suggest CaV1.2 and CaV1.3 channels as potential targets for anti-diabetes therapy.

A Selectivity Filter Gate Controls Voltage-Gated Calcium Channel Calcium-Dependent Inactivation

“…To investigate this possibility, we compared low-noise recordings from the DII (+1) mutants that exhibited the most severe, D707A, and the mildest, D707N, CDI loss with Ca V 1.2. Because of the challenges associated with single Ca V channel recordings when Ca 2+ is the charge carrier (Hess et al, 1984), we compared patches expressing Ca V 1.2, D707A, and D707N using Ba 2+ as the charge carrier as in many prior studies (Adams et al, 2014;Bock et al, 2011;Dick et al, 2016;Doering et al, 2005;Hess et al, 1984;Tadross et al, 2008Tadross et al, , 2013Yang et al, 2015). These experiments showed single Ca V 1.2 channels having an $1-pA current amplitude, consistent with prior reports (Dick et al, 2016).…”

Role of High Voltage-Gated Ca2+ Channel Subunits in Pancreatic β-Cell Insulin Release. From Structure to Function

“…One possible explanation for the observed discrepancies between the two mouse models is that the β-cells are an inhomogeneous population with only a subset of cells expressing Ca V 1.3 channels. In fact, a recent study has demonstrated using single channel recordings that onlỹ 20% of β-cells express Ca V 1.3 channels [87]. Additionally, it has been shown that Ca V 1.3 channels have a lower dihydropyridine sensitivity compared to Ca V 1.2 [88]; therefore, some of the pharmacology experiments might have underestimated the contribution of Ca V 1.3 to the total β-cell Ca 2+ influx.…”

A Phenotypic Screen Identifies Calcium Overload as a Key Mechanism of β-Cell Glucolipotoxicity

“…In mice expressing a mutant form of Abcc8, a key component of the b-cell K ATP channel showing constant depolarization similar to that observed with nutrient overload, intracellular calcium is constantly elevated, leading to diabetes (24). Furthermore, mouse islet cells exposed to diabetic serum show hyperactivation of L-type calcium channels (25).…”