Alpha-adrenergic agonist and endothelin-1 induced intracellular Ca2+ response in the presence of a Ca2+ entry blocker in cultured rat ventricular myocytes

Capacitative calcium entry contributes to nuclear factor of activated T-cells nuclear translocation and hypertrophy in cardiomyocytes

In nonexcitable cells, depletion of endoplasmic reticulum Ca(2+) stores leads to activation of plasma membrane Ca(2+) channels, a process termed capacitative Ca(2+) entry. Here, we demonstrate that this pathway functions in cells that also contain voltage-gated Ca(2+) channels, neonatal rat ventricular myocytes. The depletion of sarcoplasmic reticulum Ca(2+) stores elicited a prolonged increase in cytoplasmic Ca(2+) dependent on extracellular Ca(2+). Inhibitors of store-operated channels but not L-type channels diminished this response. The importance of this pathway to cardiac hypertrophy, which often is dependent on Ca(2+)/calmodulin-dependent transcription factors, was also assessed in this model. Hypertrophy and atrial natriuretic factor expression induced by angiotensin II or phenylephrine was more effectively attenuated by inhibitors of capacitative entry than of L-type channels. Additionally, cardiomyocytes were transfected with a construct encoding a fluorescent nuclear factor of activated T-cells chimeric protein to follow nuclear localization in response to thapsigargin, angiotensin II, and phenylephrine. This translocation was completely prevented by inhibitors of capacitative Ca(2+) entry and only partially abrogated by inhibitors of L-type channels. In contrast, a hypertrophic response induced by overexpression of the transcription factor MEK1 was unaffected by inhibitors of capacitative entry. Together, these data suggest a role for CCE in cardiomyocyte physiology and, in particular, in Ca(2+)-mediated cardiac hypertrophy.

The influence of phenylephrine outward potassium currents in single smooth muscle cells from the rabbit mesenteric artery

In mesenteric artery smooth muscle cells, depolarizing voltage steps activated outward K+ currents whose amplitude was decreased by about 20% with phenylephrine (1-10 microM: n = 14 cells). Attenuation of outward current was only partly dependent on [Ca2+]i, because it persisted, although reduced, with 10 mM BAPTA in the patch pipette and was abolished in the presence of 3 mM 3,4-diaminopyridine (n = 13). In outside-out patches, phenylephrine did not exert any direct effect on the unitary current amplitude or open probability of large conductance K+ channels. Outward current was significantly increased (>100% in both cases) by 10 mM caffeine, presumably owing to the release of internal Ca2+ stores. With 10 mM BAPTA in the pipette, the only response to caffeine was a small decrease (9 +/- 3.7%, n = 10) in the K+ current. These observations show that a minor effect of phenylephrine is to reduce outward K+ current (probably Kv) in mesenteric cells.

Comparative effects of endothelin and neurotensin on intrinsic cardiac neurons in situ

Studies were performed on anesthetized dogs to determine whether the peptides endothelin and neurotensin influence intrinsic cardiac neurons in situ and, if so, whether intrinsic cardiac neurons sensitive to these peptides are involved in cardiac regulation. Endothelin-1 (0.1 ml, 100 nM), which has high affinity for ETA endothelin receptors, when administered to a population of right atrial neurons via their regional arterial blood supply increased neuronal activity (+173%), heart rate (+18%), as well as right (62%) and left ventricular (14%) intramyocardial systolic pressures in 12 dogs so tested. When the selective ETB endothelin receptor agonist BQ-3020 (0.1 ml, 100 nM) was applied to these neurons their activity increased (+119%) in 10 of 12 dogs tested, as did right (56%) and left (12%) ventricular intramyocardial systolic pressures. Neuronal and cardiac responses were induced by BQ-3020, but not by endothelin-1, in the presence of a selective ETA receptor antagonist (BQ-610). When a greater dose of endothelin-1 (0.1 ml. 10 microM) was administered to right atrial neurons in tour separate dogs, alterations in neuronal activity were accompanied by ventricular arrhythmias that progressed to ventricular fibrillation. In contrast, when neurotensin (0.1 ml, 10 microM) was administered into their regional arterial blood supply intrinsic cardiac neurons were excited without cardiac variables being affected. These data indicate that: 1) mammalian intrinsic cardiac neurons are sensitive to endothelin and neurotensin; 2) endothelin-sensitive intrinsic cardiac neurons possess ETA and ETB receptors; 3) cardiac indices are enhanced when intrinsic cardiac neurons sensitive to endothelin, not neurotensin, become activated.