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Biophys J, July 2002, p. 229-241, Vol. 83, No. 1

Cloning and Expression of the Human T-Type Channel Cav3.3: Insights into Prepulse Facilitation

Juan Carlos Gomora, Janet Murbartián, Juan Manuel Arias, Jung-Ha Lee, and Edward Perez-Reyes

Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908 USA

The full-length human Cav3.3 (alpha 1I) T-type channel was cloned, and found to be longer than previously reported. Comparison of the cDNA sequence to the human genomic sequence indicates the presence of an additional 4-kb exon that adds 214 amino acids to the carboxyl terminus and encodes the 3' untranslated region. The electrophysiological properties of the full-length channel were studied after transient transfection into 293 human embryonic kidney cells using 5 mM Ca2+ as charge carrier. From a holding potential of -100 mV, step depolarizations elicited inward currents with an apparent threshold of -70 mV, a peak of -30 mV, and reversed at +40 mV. The kinetics of channel activation, inactivation, deactivation, and recovery from inactivation were very similar to those reported previously for rat Cav3.3. Similar voltage-dependent gating and kinetics were found for truncated versions of human Cav3.3, which lack either 118 or 288 of the 490 amino acids that compose the carboxyl terminus. A major difference between these constructs was that the full-length isoform generated twofold more current. These results suggest that sequences in the distal portion of Cav3.3 play a role in channel expression. Studies on the voltage-dependence of activation revealed that a fraction of channels did not gate as low voltage-activated channels, requiring stronger depolarizations to open. A strong depolarizing prepulse (+100 mV, 200 ms) increased the fraction of channels that gated at low voltages. In contrast, human Cav3.3 isoforms with shorter carboxyl termini were less affected by a prepulse. Therefore, Cav3.3 is similar to high voltage-activated Ca2+ channels in that depolarizing prepulses can regulate their activity, and their carboxy termini play a role in modulating channel activity.

Biophys J, July 2002, p. 229-241, Vol. 83, No. 1
© 2002 by the Biophysical Society   0006-3495/02/07/229/13  $2.00


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