Novel functional properties of Ca2+ channel β subunits revealed by their expression in adult rat heart cells

Henry M. Colecraft, Badr Alseikhan, Shoji X. Takahashi, Dipayan Chaudhuri, Scott Mittman, Vasan Yegnasubramanian, Rebecca S. Alvania, David C. Johns, Eduardo Marbán, David T. Yue

Research output: Contribution to journalArticlepeer-review

Abstract

Recombinant adenoviruses were used to overexpress green fluorescent protein (GFP)-fused auxiliary Ca2+ channel β subunits(β14) in cultured adult rat heart cells, to explore new dimensions of β subunit functions in vivo. Distinct β-GFP subunits distributed differentially between the surface sarcolemma, transverse elements, and nucleus in single heart cells. All β-GFP subunits increased the native cardiac whole-cell L-type Ca2+ channel current density, but produced distinctive effects on channel inactivation kinetics. The degree of enhancement of whole-cell current density was non-uniform between β subunits, with a rank order of potency β2a ≈ β4 > β1b > β3. For each β subunit, the increase in L-type current density was accompanied by a correlative increase in the maximal gating charge (Qmax) moved with depolarization. However, β subunits produced characteristic effects on single L-type channel gating, resulting in divergent effects on channel open probability (Po). Quantitative analysis and modelling of single-channel data provided a kinetic signature for each channel type. Spurred on by ambiguities regarding the molecular identity of the actual endogenous cardiac L-type channel β subunit, we cloned a new rat β2 splice variant, β2b, from heart using 5′ rapid amplification of cDNA ends (RACE) PCR. By contrast with β2a, expression of β2b in heart cells yielded channels with a microscopic gating signature virtually identical to that of native unmodified channels. Our results provide novel insights into β subunit functions that are unattainable in traditional heterologous expression studies, and also provide new perspectives on the molecular identity of the β subunit component of cardiac L-type Ca2+ channels. Overall, the work establishes a powerful experimental paradigm to explore novel functions of ion channel subunits in their native environments.

Original languageEnglish (US)
Pages (from-to)435-452
Number of pages18
JournalJournal of Physiology
Volume541
Issue number2
DOIs
StatePublished - Jun 1 2002

ASJC Scopus subject areas

  • Physiology

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