Article

Ritanserin blocks CaV1.2 channels in rat artery smooth muscles: electrophysiological, functional, and computational studies

Authors: Fabio Fusi1, Alfonso Trezza1, Giampietro Sgaragli2, Ottavia Spiga1, Simona Saponara2, Sergio Bova3
1 Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, via A. Moro 2, 53100 Siena, Italy
2 Dipartimento di Scienze della Vita, Università degli Studi di Siena, via A. Moro 2, 53100 Siena, Italy
3 Dipartimento di Scienze del Farmaco, Università degli Studi di Padova, via Marzolo 5, 35131 Padova, Italy
Correspondence to: Simona Saponara: simona.saponara@unisi.it,
DOI: 10.1038/s41401-020-0370-1
Received: 17 October 2019
Accepted: 19 January 2020
Advance online: 4 March 2020

Abstract

CaV1.2 channel blockers or 5-HT2 receptor antagonists constitute effective therapy for Raynaud’s syndrome. A functional link between the inhibition of 5-HT2 receptors and CaV1.2 channel blockade in arterial smooth muscles has been hypothesized. Therefore, the effects of ritanserin, a nonselective 5-HT2 receptor antagonist, on vascular CaV1.2 channels were investigated through electrophysiological, functional, and computational studies. Ritanserin blocked CaV1.2 channel currents (ICa1.2) in a concentration- dependent manner (Kr = 3.61 μM); ICa1.2 inhibition was antagonized by Bay K 8644 and partially reverted upon washout. Conversely, the ritanserin analog ketanserin (100 μM) inhibited ICa1.2 by ~50%. Ritanserin concentration-dependently shifted the voltage dependence of the steady-state inactivation curve to more negative potentials (Ki = 1.58 μM) without affecting the slope of inactivation and the activation curve, and decreased ICa1.2 progressively during repetitive (1 Hz) step depolarizations (use- dependent block). The addition of ritanserin caused the contraction of single myocytes not yet dialyzed with the conventional method. Furthermore, in depolarized rings, ritanserin, and to a lesser extent, ketanserin, caused a concentration-dependent relaxation, which was antagonized by Bay K 8644. Ritanserin and ketanserin were docked at a region of the CaV1.2 α1C subunit nearby that of Bay K 8644; however, only ritanserin and Bay K 8644 formed a hydrogen bond with key residue Tyr-1489. In conclusion, ritanserin caused in vitro vasodilation, accomplished through the blockade of CaV1.2 channels, which was achieved preferentially in the inactivated and/or resting state of the channel. This novel activity encourages the development of ritanserin derivatives for their potential use in the treatment of Raynaud’s syndrome.
Keywords: ritanserin; CaV1.2 channel; Raynaud s syndrome; 5-HT2 receptor; docking simulation; homology modeling

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