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

Abstract

Objective: T-type Ca²⁺ currents (I_Ca-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 α-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 α-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 I_Ca-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, I_Ca-T was separated from I_Ca-L by different holding potentials (HP). I_Ca-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 μM tetrodotoxin (TTX). Results: The T-type Ca²⁺ channel gene α-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; PI_Ca-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. I_Ca-T was not detected in any of 21 sham cells. I_Ca-T density was 1.1±0.4 pA/pF. I_Ca-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.