Splice-variant changes of the Ca_V3.2 T-type calcium channel mediate voltage-dependent facilitation and associate with cardiac hypertrophy and development

Abstract

Low voltage-activated T-type calcium (Ca) channels contribute to the normal development of the heart and are also implicated in pathophysiological states such as cardiac hypertrophy. Functionally distinct T-type Ca channel isoforms can be generated by alternative splicing from each of three different T-type genes (Ca(V)3.1, Ca(V)3.2,Ca(V)3.3), although it remains to be described whether specific splice variants are associated with developmental states and pathological conditions. We aimed to identify and functionally characterize Ca(V)3.2 T-type Ca channel alternatively spliced variants from newborn animals and to compare with adult normotensive and spontaneously hypertensive rats (SHR). DNA sequence analysis of full-length Ca(V)3.2 cDNA generated from newborn heart tissue identified ten major regions of alternative splicing, the more common variants of which were analyzed by quantitative real-time PCR (qRT-PCR) and also subject to functional examination by whole-cell patch clamp. The main findings are that: (1) cardiac Ca(V)3.2 T-type Ca channels are subject to considerable alternative splicing, (2) there is preferential expression of Ca(V)3.2(-25) splice variant channels in newborn rat heart with a developmental shift in adult heart that results in approximately equal levels of expression of both (+25) and (-25) exon variants, (3) in the adult stage of hypertensive rats there is a both an increase in overall Ca(V)3.2 expression and a shift towards expression of Ca(V)3.2(+25) containing channels as the predominant form, and (4) alternative splicing confers a variant-specific voltage-dependent facilitation of Ca(V)3.2 channels. We conclude that Ca(V)3.2 alternative splicing generates significant T-type Ca channel structural and functional diversity with potential implications relevant to cardiac developmental and pathophysiological states.

Caveolin-3 Overexpression Attenuates Cardiac Hypertrophy via Inhibition of T-type Ca2+ Current Modulated by Protein Kinase Cα in Cardiomyocytes

“…Re-expression of fetal I Ca, T in the ventricular myocytes during pathological hypertrophy is well established (22,23,42). Studies have demonstrated the expression of the Ca v 3.2 (␣ 1H ) channel current responsible for the development of cardiac hypertrophy (27,44) and the expression of the Ca v 3.1 (␣ 1G ) channels is attributed to anti-hypertrophic effect and cardioprotective function (45). It was reported that in pathological hypertrophy the Ca 2ϩ influx via the re-expressed Ca v 3.2 channel initiates the binding of calcineurin to the C terminus of Ca v 3.2 leading to activation of NFAT (46).…”

Caveolin-3 Regulates Protein Kinase A Modulation of the CaV3.2 (α1H) T-type Ca2+ Channels

“…Of the three different T-type Ca 2ϩ channel isoforms reported, alternative splicing of the Ca v 3.2 channels results in functional diversity of the channel during cardiac development (47). Recent findings using a heterologous expression system of HEK293 cells suggest a complex regulation for the Ca v 3.2 channels.…”

T-type calcium channel expression and function in the diseased heart

“…69 The expression of Ca V 3.2 splice variants was found to be regulated during development, as well as in the LV of hypertrophic rat hearts. Furthermore, splice variants of Ca V 3.2 channels displayed alterations in function that could be relevant with respect to contractile performance in the diseased heart.…”