Roles of a Membrane-localized Subunit in the Formation and Targeting of Functional L-type Ca Channels

doi:10.1074/jbc.270.50.30036

Roles of a Membrane-localized Subunit in the Formation and Targeting of Functional L-type Ca Channels (*)

From the (1) Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611 and the
(2) Department of Physiology, Rush University, Chicago, Illinois 60612

** To whom correspondence should be addressed:
Dept. of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, 303 E. Chicago Ave. S215, Chicago, IL 60611.
Tel.: 312-503-3692; Fax: 312-503-5349; mhosey{at}nwu.edu.

↵^¶ Permanent address: A. A. Bogomoletz Institute of Physiology, Ukrainian Academy of Sciences, Kiev 252024, Ukraine.

Abstract

We report several unexpected findings that provide novel insights into the properties and interactions of the α¹ and β subunits of dihydropyridine-sensitive L-type channels. First, the β subunit was expressed as multiple species of 68-72 kDa; the 70-72-kDa species arose from post-translational modification. Second, cell fractionation and immunocytochemical studies indicated that the hydrophilic β subunit, when expressed alone, was membrane-localized. Third, the β subunit increased the membrane localization of the α¹ subunit and the number of cells expressing L-type Ca currents, without affecting the total amount of the expressed α subunit. Expression of maximal currents in α/β co-transfected cells paralleled the time course of expression of the β subunit. Taken together, these results suggest that the β subunit plays multiple roles in the formation, stabilization, targeting, and modulation of L-type channels.

Footnotes

↵^§ Supported by National Research Service Award Predoctoral Training Grant 5 T32 ES07124 in the Environmental Sciences.
↵* This work was supported in part by National Institutes of Health Grants HL23306 (to M. M. H.) and AR43113 (to E. R.), and by grants from the American Heart Association (to E. R.) and the American Heart Association of Metropolitan Chicago (to R. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

HEK

human embryonic kidney

FITC

fluorescein isothiocyanate

TRITC

tetramethyl rhodamine isothiocyanate

DMEM

Dulbecco's modified Eagle's medium

PCR

polymerase chain reaction

DHP

dihydropyridine.
↵²T. S. Puri and M. M. Hosey, manuscript in preparation.
↵³X. Zhao, B. Gerhardstein, and M. M. Hosey, unpublished observations.
↵⁴T. Y. Gao and M. M. Hosey, unpublished observations.
↵⁵T. J Kamp and E. Marban, personal communication.
↵⁶R. E. Shirokov, G. Ferreira, J. Yi, J. Zhou, A. J. Chien, M. M. Hosey, and E. Rios, manuscript in preparation.
- Received August 23, 1995.
- Revision received October 6, 1995.