Modified Sympathetic Nerve System Activity with Overexpression of the Voltage-dependent Calcium Channel β3 Subunit

Abstract

N-type voltage-dependent calcium channels (VDCCs) play determining roles in calcium entry at sympathetic nerve terminals and trigger the release of the neurotransmitter norepinephrine. The accessory ␤3 subunit of these channels preferentially forms N-type channels with a pore-forming CaV2.2 subunit. To examine its role in sympathetic nerve regulation, we established a ␤3-overexpressing transgenic (␤3-Tg) mouse line. In these mice, we analyzed cardiovascular functions such as electrocardiography, blood pressure, echocardiography, and isovolumic contraction of the left ventricle with a Langendorff apparatus. Furthermore, we compared the cardiac function with that of ␤3-null and CaV2.2 (␣1B)-null mice. The ␤3-Tg mice showed increased expression of the ␤3 subunit, resulting in increased amounts of CaV2.2 in supracervical ganglion (SCG) neurons. The ␤3-Tg mice had increased heart rate and enhanced sensitivity to N-type channel-specific blockers in electrocardiography, blood pressure, and echocardiography. In contrast, cardiac atria of the ␤3-Tg mice revealed normal contractility to isoproterenol. Furthermore, their cardiac myocytes showed normal calcium channel currents, indicating unchanged calcium influx through VDCCs. Langendorff heart perfusion analysis revealed enhanced sensitivity to electric field stimulation in the ␤3-Tg mice, whereas ␤3-null and Cav2.2-null showed decreased responsiveness. The plasma epinephrine and norepinephrine levels in the ␤3-Tg mice were significantly increased in the basal state, indicating enhanced sympathetic tone. Electrophysiological analysis in SCG neurons of ␤3-Tg mice revealed increased calcium channel currents, especially N-and L-type currents. These results identify a determining role for the ␤3 subunit in the N-type channel population in SCG and a major role in sympathetic nerve regulation.Voltage-dependent Ca 2ϩ channels (VDCCs) 2 are present in excitable tissues. VDCCs mediate the influx of Ca 2ϩ in response to membrane depolarization and regulate many fundamental functions, including muscle contraction, neurotransmitter release, and gene transcription (1). The VDCC ␣1 subunit families are classified into three main groups (CaV1.1-4, CaV2.1-3, and CaV3.1-3) based on their physiological properties and sequence similarities (2). VDCCs are heteromultimeric proteins, composed of four subunits (␣1, ␣2/␦, ␤, and ␥). The ␣1 subunit serves as the channel pore, voltage sensor, and the binding site for various channel modulators (1, 3). The ␤ subunit, which is hydrophilic and has no transmembrane domain, is the most important auxiliary subunit in the VDCC complex, with four different genes having been identified. The ␤ subunits have distant homology with the Src homology region 3 and guanylate kinase module, which interact with the ␣1 subunit (4).Several important roles of the ␤ subunit in channel properties, such as multifold increases in peak calcium current density and acceleration of inactivation kinetics, have been demonstrated using heterologous cDNA co-expression systems (5, ...

The β Subunit of Voltage-Gated Ca2+Channels

“…Also, a high-salt diet causes elevation of blood pressure, reduction in plasma catecholamine levels, and a hypertrophy of heart and aortic smooth muscle (328, ). The latter effects, as well as observations from mice overexpressing β 3 (327), are consistent with a function of β 3 in sympathetic control. In this regard, β 3 knockouts resemble N-type channel (Ca v 2.2) knockouts (428, ), which is not surprising since N-type channels preferably partner with β 3 (294, 325–327, 395).…”

“…The latter effects, as well as observations from mice overexpressing β 3 (327), are consistent with a function of β 3 in sympathetic control. In this regard, β 3 knockouts resemble N-type channel (Ca v 2.2) knockouts (428, ), which is not surprising since N-type channels preferably partner with β 3 (294, 325–327, 395). Indeed, sympathetic neurons from β 3 -null mice have reduced N- and L-type channels activity (330).…”

Cilnidipine suppresses podocyte injury and proteinuria in metabolic syndrome rats: possible involvement of N-type calcium channel in podocyte

“…N-type calcium channel are known to be expressed in the nerve endings and to be implicated in the regulation of nerve activity by maintaining the intra-cellular calcium level [27]. However, few studies have explored the role of N-type calcium channel expressing in the other cells.…”

Effects of Propofol on Electrocardiogram Measures in Mice

“…Total RNA isolation from the entire heart, reverse transcription reactions, and PCR amplifications were performed using standard methods (18). To avoid contamination with genomic DNA in RT-PCR analysis, each primer set was designed to span at least one intron.…”