Cloning, functional expression, and distribution of three c
-terminal splice variants of a human cardiac l-type ca2+ channel
[alpha]1 subunit.
Klsckner, U., G. Mikala, J. Eisfeld, D. E. Iles, M. Strobeck, J. L.
Mershon, A. Schwartz, and G. Varadi.
Institute of Molecular Pharmacology and Biophysics, University of
Cincinnati, 231 Bethesda Avenue, P.O.Box 670828, Cincinnati, Ohio,
45267-0828, USA, Department of Physiology, UniversitSt zu Ksln,
Robert-Koch-Strasse 39, 50931 Ksln, Germany, Department of Cell
Biology and Histology, Katholieke Universiteit Nijmegen, Nijmegen,
The Netherlands
APStracts 3:0453H, 1996.
There is growing evidence for diversity of cardiac type (class C)
voltage-dependent calcium channel [alpha]1 subunits arising from the
alternative splicing of a primary transcript. In this study, we show
the existence of carboxy terminal variability in the human cardiac
[alpha]1 gene by genomic cloning. We found that the genomic DNA
segment encoding the C-terminal tail of the protein is composed of
nine invariable and two alternative exons. The alternative
utilization of these latter two exons gives rise to the formation of
three message variants for this region. Reverse transcription
followed by PCR and radioanalytical quantitation of the RT/PCR
products showed significant variations in the distribution of these
isoforms (hHt[alpha]1, rHt[alpha]1, fHt[alpha]1) in distinct parts of
the heart, the aorta and fibroblasts. Expression of the three
[alpha]1 isoforms in Xenopus oocytes or in HEK293 cells and analysis
of the kinetics and voltage-dependence of the induced calcium channel
currents revealed only insignificant differences in the behavior of
these isoforms. When the [alpha]1 isoforms were co-expressed with a
human [beta] subunit, no [alpha]1-specific divergences were observed
but effects of [beta] subunit co-expression on [alpha]1 isoform
biophysical properties were confirmed. The differential abundance of
the three isoforms and the influence of an accessory subunit, are of
potential physiological significance.
Received 3 August 1994; accepted in final form 10 September 1996.
APS Manuscript Number H693-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996