Atrial natriuretic peptide antagonizes endothelin-induced calcium increase and cell contraction in cultured human hepatic stellate cells

Abstract

Several lines of evidence indicate that hepatic stellate cells (HSCs), besides their crucial role in the increased synthesis of extracellular matrix components that occurs in chronic liver diseases, may participate in the regulation of sinusoidal blood flow. [1][2][3] Morphological studies have shown that HSCs have numerous cell processes that surround the sinusoids and contain cytosolic proteins characteristic of contractile cells. [4][5][6][7][8][9][10] Moreover, HSCs have receptors for a large number of vasoconstrictor substances, including endothelin-1, arginine vasopressin, thrombin, thromboxanes, and angiotensin II. 6,8,[11][12][13][14][15] Finally, the stimulation of HSCs in culture with these vasoconstrictor substances is associated with a marked increase in intracellular calcium concentration ([Ca 2ϩ ] i ) and cell contraction, 6,[8][9][10][11][12][13][14][15] suggesting that the contractile function of HSCs may be regulated by the action of vasoconstrictors.In contractile cells, the effects of vasoconstrictor agonists may be attenuated by the action of vasodilators. In fact, the state of contraction/relaxation of contractile cells is dependent on the interaction between vasoconstrictor and vasodilator factors. 16 In clear contrast with the large amount of information available on the effects of vasoconstrictor factors on HSCs, little is known about the effects of vasodilating substances on these cells. It has been shown that prostaglandins and nitric oxide produce relaxation of HSCs in culture and reduce the effects of vasoconstrictor agents, which suggests that these vasodilator factors may act as paracrine or autocrine regulators of HSCs' contractility. 10,12 However, it is not known whether the contractile function of HSCs may also be regulated by circulating vasodilator substances. One of the most important circulating vasodilators is atrial natriuretic peptide (ANP), a peptide synthesized in atrial myocytes, which besides its potent natriuretic action has important effects in the circulation by antagonizing the effects of vasoconstrictors. 17,18 Therefore, the aims of the current study were to determine (1) whether human HSCs have receptors for ANP, and (2) whether the stimulation of human HSCs with ANP in vitro reduces the effects elicited by contractile agonists on these cells. MATERIALS AND METHODSIsolation and Culture of Human and Rat Hepatic Stellate Cells. Human HSCs were isolated from fragments of normal human livers obtained from resections of liver metastases as described in detail elsewhere. 15,19 Briefly, after a combined digestion of liver tissue with

In Vitro And In Vivo Activation of Rat Hepatic Stellate Cells Results In De Novo Expression of L–Type Voltage–Operated Calcium Channels

“…13,27 This reduction in cell area induced by vasoconstrictors is antagonized by preincubation of cells with vasodilator factors, such as nitric oxide, prostaglandins, or atrial natriuretic peptides. 28,29 Moreover, a close relationship between Ca 2ϩ mobilization and reduction in cell area in human HSCs has been shown. 12 Quiescent HSCs showed neither changes in [Ca 2ϩ ] i nor cell contraction after stimulation with KCl, despite a marked cell membrane depolarization, indicating the lack of functional VOCC.…”

Hepatic Stellate Cells: Protean, Multifunctional, and Enigmatic Cells of the Liver

“…Relaxants include NO (342), C-type and atrial natriuretic peptides (205,637), which regulate calcium signaling following interaction with its receptor, as well as carbon monoxide generated by stellate cellderived heme oxygenase (350,623).…”

Atrial Natriuretic Peptide Attenuates Elevations in Ca2+ and Protects Hepatocytes by Stimulating Net Plasma Membrane Ca2+ Efflux

“…Natriuretic peptides attenuate elevations in cytosolic free Ca 2ϩ concentration ([Ca 2ϩ ] c ) in many cell types (37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50), including rat hepatocytes (51). Atrial natriuretic peptide (ANP) 3 is a circulating hormone released mainly by atrial myocytes (52) in response to stress conditions such as volume expansion or cardiac hypoxia.…”

“…Similarly, calpain activation plays a key role in cellular injury in diverse pathologies, including oxidant-induced pancreatic acinar cell injury (27), myocardial ischemia-reperfusion injury (128), neurotoxicity (129), spinal cord injury (28), and endothelial dysfunction in type 2 diabetes (29). Because natriuretic peptides act on several organs (54) and attenuate elevations in [Ca 2ϩ ] c in many cell types (37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50), it is unlikely that their cytoprotective effects are restricted to liver. Indeed, natriuretic peptides may have an in vivo role as circulating inhibitors of pathophysiological elevations in [Ca 2ϩ ] c and calpain activity.…”