To determine a possible role for NCX in myogenically active smooth muscle arterioles, studies were conducted by manipulation of extracellular Na+ levels and inhibition of the exchanger. Western blotting was performed for the identification of the NCX protein. Real-time PCR was performed to demonstrate the level of expression of mRNA, for the NCX isoforms. Antisense oligonucleotides against NCX mRNA were introduced in an isolated cremaster arteriole followed by functional studies after 24 hours. Level of expression of NCX was determined by western blotting. The data are consistent with the presence of NCX1 in the cremaster arterioles.

This study investigated the effects of SEA0400, a Na+/Ca2+ exchange inhibitor, in cardioplegia on rat myocyte contractile function. SEA0400 significantly reduced the accumulation of diastolic Ca2+ throughout cardioplegic arrest compared to ischemic control and cardioplegia. Cells treated with SEA0400 during cardioplegic arrest showed significantly larger Ca2+ transient amplitudes and contractions throughout reperfusion compared to cells treated with cardiopelgia alone. Intracellular Ca2+ stores were similar in both cardioplegic groups at baseline and during reperfusion. Together these results suggest that SEA0400 has beneficial effects at protecting ventricular myocytes during cardioplegic arrest and that SEA0400 in cardioplegia may affect myofilament Ca2+ sensitivity.

No / Catecholamines that accompany acute physiological stress are also involved in mediating the development of hypertrophy and failure. However, the cellular mechanisms involved in catecholamine-induced cardiac hypertrophy, particularly Ca2+ handling, are largely unknown. We therefore investigated the effects of cardiac hypertrophy, produced by isoprenaline, on INa/Ca and sarcoplasmic reticulum (SR) function in isolated myocytes. Methods: INa/Ca was studied in myocytes from Wistar rats, using descending (+80 to ¿110 mV) voltage ramps under steady state conditions. Myocytes were also loaded with fura-2 and either field stimulated or voltage clamped to assess [Ca2+]i and SR Ca2+ content. Results: Ca2+-dependent, steady state INa/Ca density was increased in hypertrophied myocytes (P<0.05). Ca2+ release from the SR was also increased, whereas resting [Ca2+]i and the rate of decline of [Ca2+]i to control levels were unchanged. SR Ca2+ content, estimated by using 10.0 mmol/l caffeine, was also significantly increased in hypertrophied myocytes, but only when myocytes were held and stimulated from their normal resting potential (¿80 mV) but not from ¿40 mV. However, the rate of decline of caffeine-induced Ca2+ transients or INa/Ca was not significantly different between control and hypertrophied myocytes. Ca2+-dependence of INa/Ca, examined by comparing the slope of the descending phase of the hysteresis plots of INa/Ca vs. [Ca2+]i, was also similar in the two groups of cells. Conclusion: Data show that SR Ca2+ release and SR Ca2+ content were increased in hypertrophied myocytes, despite an increase in the steady state INa/Ca density. The observation that increased SR function occurred only when myocytes were stimulated from ¿80 mV suggests that Na+ influx may play a role in altering Ca2+ homeostasis in hypertrophied cardiac muscle, possibly through increased reverse Na+/Ca2+ exchange, particularly at low stimulation frequencies.

Our previous work in cultured cells has shown that the maintenance of mitochondrial Ca2+ homeostasis is essential for cell survival, and that the anti-apoptotic protein Bcl-2 is able to maintain a threshold level of mitochondrial Ca2+ by the inhibition of permeability transition. To test whether Bcl-2 also affects the mitochondrial Na+-Ca2+ exchange (NCE), a major efflux pathway for mitochondrial Ca2+, studies using transgenic mice that overexpress Bcl-2 in the heart have been performed. NCE activity was determined as the Na+-dependent Ca2+ efflux in the isolated mitochondria. Overexpression of Bcl-2 led to a significant reduction of NCE activity as well as increased resistance to permeability transition in the mitochondria of transgenic heart. This was accompanied by increased matrix Ca2+ level, enhanced formation of NADH and enhanced oxidation of pyruvate, an NAD+-linked substrate. Furthermore, there was induction of cellular Ca2+ transport proteins including the Na+-Ca2+ exchanger of the sarcolemma (NCX). Bcl-2 not only stimulates NCX expression in the sarcolemma but also attenuates the Na+-Ca2+ exchange in the mitochondria. These results are consistent with the protection by Bcl-2 against apoptosis in heart following ischemia/reperfusion.