Trp-His, a vasorelaxant di-peptide, can inhibit extracellular Ca2+ entry to rat vascular smooth muscle cells through blockade of dihydropyridine-like l-type Ca2+ channels

Our previous findings regarding the biological activities of small peptides revealed that a di-peptide, Trp-His (WH), could play a role in the prevention of vascular lesions, including cell proliferation and atherosclerosis. Its vasoprotective effects could be associated with suppression of the vasocontraction signaling cascade, but the underlying mechanism(s) remains obscure. In this study, we attempted to elucidate the vasoprotective mechanism of WH, in opposing the proliferation of rat vascular smooth muscle cells (VSMCs). In VSMCs from 8 week-old male Wistar rat thoracic aortae, WH evoked a significant dose-dependent anti-proliferation effect, without cytotoxicity. In mitogen-stimulated cell experiments, 300 μM WH inhibited cytosolic Ca2+ elevation in VSMCs induced by 10 μM angiotensin II (Ang II). Furthermore, WH suppressed extracellular Ca2+ entry into CaCl2-stimulated VSMCs. The biological capacity of WH as an intracellular Ca2+ ([Ca2+]i) suppressor was also proven when 50 μM Bay K8644 was used to enhance Ca2+ entry via a voltage-dependent l-type Ca2+ channel (VDCC) and 300 μM WH elicited a 23% reduction in [Ca2+]i. The absence of a reduction of the [Ca2+]i by the mixture of tryptophan and histidine revealed the importance of the peptide backbone in the [Ca2+]i reduction effect. Furthermore, the WH-induced [Ca2+]i reduction was abolished by verapamil, but not by nifedipine, indicating that WH likely binds to an extracellular site of the VDCC at a site similar to that of the dihydropyridine type-Ca2+ channel blockers.

Research highlights▶ L-type Ca2+ channel agonist stimulates Ca2+ influx into smooth muscle cells. ▶ Trp-His prevents the elevation of intracellular Ca2+ concentration. ▶ Trp-His binds to the extracellular site of L-type Ca2+ channel proteins.