Reexpression of T-type Ca2+ channel gene and current in post-infarction remodeled rat left ventricle

Objective: T-type Ca2+ currents (ICa-T) are present in neonatal rat myocytes but is not detected in adult ventricular myocytes. The present study was designed to investigate the expression of the T-type Ca2+ channel gene and current in post-infarction remodeled hypertrophied rat left ventricle (LV). Methods: We compared the expression of T-type Ca2+ channel gene alpha-1G in neonatal rat LV, in adult sham-operated LV and remodeled hypertrophied LV 3 to 4 weeks post-myocardial infarction (MI) using RNase protection assay (RPA). The cDNA fragment of alpha-1G used in RPA was obtained from poorly conserved region of recently published T-type Ca2+ channel coding sequence of rat by RT-PCR. The fragment was verified by restriction enzyme digestion and sequencing. The presence of ICa-T in LV of sham and post-MI rats was examined using patch-clamp techniques. In the presence of K+-free, Na+-free external solution, ICa-T was separated from ICa-L by different holding potentials (HP). ICa-T was also recorded during depolarization to -40 mV from a HP of -80 mV with NaCl in external solution and I-Na suppressed by 100 mu M tetrodotoxin (TTX). Results: The T-type Ca2+ channel gene alpha-1G was expressed in neonatal heart, the expression level decreased by 80%, in adult sham heart and was reexpressed in MI (158% increases compared to sham; P<0.01). ICa-T was recorded in 11 of 31 MI cells in presence of K+-free, Na+-free external solution and in 9 of 14 cells when I-Na was suppressed by TTX. ICa-T was not detected in any of 21 sham cells. ICa-T density was 1.1+/-0.4 pA/pF. ICa-T was more sensitive to Ni2+ and less sensitive to nisoldipine. Conclusions: T-type Ca2+ channel gene and current are reexpressed in rat post-MI remodeled LV myocytes. Its functional significance in the post-MI remodeling process remains to be defined. (C) 2000 Elsevier Science B.V. All rights reserved.