Effects of Endothelin A Receptor Antagonist to Cellular Proliferation and Apoptosis in Neonatal Rat Heart

PURPOSE: In order to investigate the role of endothelins in the cardiac development, the present study was designed to examine the effects of endothelin A receptor(ETAR) antagonist to the cellular proliferation and apoptosis in the neonatal rat heart. In addition, the expression of various regulatory genes in protein and mRNA levels by ETAR antagonist were examined. METHODS: Neonatal Spargue-Dawley rats were separated into two groups. The BMS group(N=22) was treated with the selective ETAR antagonist(Bristo-Myers Squibb-182874; 300 mg/Kg/day) and the control group(N=20) with normal saline for seven days by orogastric tube. On the following day, their hearts were harvested for determination of apoptosis by modified TUNEL technique and cellular proliferation by PCNA stain. In addition to this, Western blottings and RT-PCRs of bcl-x, clusterin, p53 and TGF-beta1 were performed. RESULTS: The BMS group resulted in a reduced body weight, but not a significantly reduced heart weight. In the BMS group, cardiac apoptotic cells and PCNA positive cells were decreased(P<0.05). In the BMS group, clusterin and bcl-x protein expressions were increased(P<0.05), but p53 and TGF-beta1 protein expressions remained the same. In the BMS group, clusterin and TGF-beta1 mRNA expressions were increased(P<0.05), but bcl-x and p53 mRNA expressions remained the same. CONCLUSION: ETAR antagonist treatment decreases cell turnover in the developing rat heart, which may account for the role of endothelins on modulating cardiac growth. These changes may be affected by clusterin and bcl-x expressions. These results support that there are some roles of endothelin and ETAR in the cellular level of early neonatal cardiac growth.

Studies on the roles of Na+/-Ca2+ exchange according to postnatal age in the negative staircase effect of the rat heart

Recent reports revealed that the Na+/-Ca2+ exchangers and feet structures of sarcoplasmic reticulum (SR) are located in close vicinity in the specific compartment. Therefore, we investigated the possibility that the Na+/-Ca2+ exchanger may decrease the tension development by transporting the Ca2+ out of the cell right after it released from SR, on the basis of this anatomical proximity. We examined the negative force-frequency relationship of the developed tension in the electrically field stimulated left atria of postnatal developing rat (1, 3 day, 1 week and 4 week old after birth). Cyclopiazonic acid (3 X 10(-5) M) treatment decreased the developed tension further according to postnatal age. Monensin (3 X 10(-6) M) treatment did not increase the maximal tension in 4 week-old rat, preserving negative staircase, while the negative staircase in the younger rat were flattened. Ca2+ depletion in the buffer elicited more suppression of the maximal tension according to the frequency in all groups except the 4 week-old group. The % decrease of the maximal developed tension of 4 week-old group at 1 Hz to that of 0.1 Hz after Na+ and Ca2+ depletion was only a half of those of the younger groups. Taken together, it is concluded that the Na+/-Ca2+ exchange transports more Ca2+ released from SR out of the cell in proportion to the frequency, and this is responsible for the negative staircase effect of the rat heart.