Sulfonylurea receptors type 1 and 2A randomly assemble to form heteromeric KATP channels of mixed subunit composition

Kim W. Chan, Adam Wheeler, L. Csanády

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

ATP-sensitive potassium (KATP) channels play important roles in regulating insulin secretion, controlling vascular tone, and protecting cells against metabolic stresses. KATP channels are heterooctamers of four pore-forming inwardly rectifying (Kir6.2) subunits and four sulfonylurea receptor (SUR) subunits. KATP channels containing SUR1 (e.g. pancreatic) and SUR2A (e.g. cardiac) display distinct metabolic sensitivities and pharmacological profiles. The reported expression of both SUR1 and SUR2 together with Kir6.2 in some cells raises the possibility that heteromeric channels containing both SUR subtypes might exist. To test whether SUR1 can coassemble with SUR2A to form functional KATP channels, we made tandem constructs by fusing SUR to either a wild-type (WT) or a mutant N160D Kir6.2 subunit. The latter mutation greatly increases the sensitivity of K ATP channels to block by intracellular spermine. We expressed, individually and in combinations, tandem constructs SUR1-Kir6.2 (S1-WT), SUR1-Kir6.2[N160D] (S1-ND), and SUR2A-Kir6.2[N160D] (S2-ND) in Xenopus oocytes, and studied the voltage dependence of spermine block in inside-out macropatches over a range of spermine concentrations and RNA mixing ratios. Each tandem construct expressed alone supported macroscopic K+ currents with pharmacological properties indistinguishable from those of the respective native channel types. Spermine sensitivity was low for S1-WT but high for S1-ND and S2-ND. Coexpression of S1-WT and S1-ND generated current components with intermediate spermine sensitivities indicating the presence of channel populations containing both types of Kir subunits at all possible stoichiometries. The relative abundances of these populations, determined by global fitting over a range of conditions, followed binomial statistics, suggesting that WT and N160D Kir6.2 subunits coassemble indiscriminately. Coexpression of S1-WT with S2-ND also yielded current components with intermediate spermine sensitivities, suggesting that SUR1 and SUR2A randomly coassemble into functional KATP channels. Further pharmacological characterization confirmed coassembly of not only S1-WT and S2-ND, but also of coexpressed free SUR1, SUR2A, and Kir6.2 into functional heteromeric channels.

Original languageEnglish
Pages (from-to)43-58
Number of pages16
JournalJournal of General Physiology
Volume131
Issue number1
DOIs
Publication statusPublished - Jan 2008

Fingerprint

Sulfonylurea Receptors
KATP Channels
Spermine
Pharmacology
Physiological Stress
Xenopus
Population
Oocytes
Blood Vessels
Adenosine Triphosphate
RNA
Insulin
Mutation

ASJC Scopus subject areas

  • Physiology

Cite this

Sulfonylurea receptors type 1 and 2A randomly assemble to form heteromeric KATP channels of mixed subunit composition. / Chan, Kim W.; Wheeler, Adam; Csanády, L.

In: Journal of General Physiology, Vol. 131, No. 1, 01.2008, p. 43-58.

Research output: Contribution to journalArticle

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