Effects of aging on Ca 2+ signaling in murine mesenteric arterial smooth muscle cells § Cristiane del Corsso a,1 , Olga Ostrovskaya b , Claire E. McAllister c , Keith Murray c , William J. Hatton c , Alison M. Gurney d , Nicholas J. Spencer a , Sean M. Wilson b, * a Department of Physiology, University of Nevada School of Medicine, Reno, NV 89557, USA b Department of Pharmacology, School of Pharmacy, University of Mississippi, University, MS 38677, USA c Department of Pharmacology, University of Nevada School of Medicine, Reno, NV 89557, USA d Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK Received 20 July 2005; received in revised form 23 November 2005; accepted 7 December 2005 Available online 18 January 2006 Abstract Pathophysiological changes in arterial smooth muscle structure and function occur with aging and there are a number of reports illustrating reductions in vascular responsiveness with aging. While much is known about arterial remodeling and functional adaptations with aging, very little is known about the biophysical adaptations in individual arterial myocytes. Cytosolic Ca 2+ signaling, involving activation of L-type Ca 2+ channels on the plasma membrane as well as InsP 3 and ryanodine receptors on the sarcoplasmic reticulum, is integral to vascular tone and reactivity. Thus, we tested the hypothesis that aging results in reductions in the functional expression of L-type channels and temporal aspects of ryanodine receptor and InsP 3 receptor Ca 2+ signaling, in mesenteric arterial smooth muscle cells isolated from 6 and 30 months old C57Bl/6 mice. Comparisons of L- type current activity were made using dialyzed, whole-cell voltage-clamp techniques and Ba 2+ as charge carrier. Ca 2+ signaling was measured using fura-2 fluorescence microscopy techniques. Cell morphological changes were also investigated using electrophysiological and immuno- cytochemical approaches. The amplitudes of L-type Ca 2+ currents were increased in older mice, but this was associated with membrane surface area increases of 50%, due to increases in cell length not cell width. Consequently, L-type Ca 2+ current densities were preserved with age, indicating functional channel expression was unchanged. In contrast, aging was associated with decrements in Ca 2+ signaling in response to either ryanodine receptor stimulation by caffeine or InsP 3 receptor activation with phenylephrine. These changes with aging may be related to the previously reported depression in myogenic reactivity. # 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Intracellular Ca 2+ ; Sarcoplasmic reticulum; Electrophysiology; Patch voltage-clamp; Arterial smooth muscle; Fura-2; Calcium channel 1. Introduction Vascular reactivity is dependent on the cytosolic [Ca 2+ ], which relies on an interplay of activation and inactivation of Ca 2+ permeable plasma membrane (PM) and sarcoplasmic reticulum (SR) ion channels (Davis and Hill, 1999; Kuriyama et al., 1998). Activation of PM Ca 2+ -permeable L-type (Ca L ) as well as non-selective cation (NSC) channels contribute to cytosolic [Ca 2+ ] increases and smooth muscle contractility (Davis and Hill, 1999; Kuriyama et al., 1998). The SR Ca 2+ stores of smooth muscle have InsP 3 receptors (InsP 3 R) and ryanodine receptors (RyR), which release Ca 2+ into the cytosol when stimulated. The spatial arrangement of these SR channels and the temporal aspects of Ca 2+ release are important to smooth muscle cell excitability (Janiak et al., 2001). Aging induces several pathophysiological changes in vascular structure and function, including increased arterial stiffness, arterial wall thickening, and reduced vascular www.elsevier.com/locate/mechagedev Mechanisms of Ageing and Development 127 (2006) 315–323 § This work was supported by the National Institutes of Health; P20 RR15581 from the National Center for Research Resources (W.J. Hatton), AG020400 (N.J. Spencer), HL40399 (Katherine Keef), and AI55642 (S.M. Wilson), Sean Wilson is also a Faculty Research Fellow of the University of Mississippi. * Corresponding author. Tel.: +1 662 915 7255; fax: +1 662 915 5148. E-mail address: Wilson@olemiss.edu (S.M. Wilson). 1 Present address. Albert Einstein College of Medicine, Department of Neuroscience, Room 712, 1410 Pelham Parkway South Bronx, NY 10461, USA. 0047-6374/$ – see front matter # 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.mad.2005.12.001