Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC119
Differential expression and function of the voltage operated calcium channels and their ancillary subunits in a mice model of essential hypertension
S. Tajada1, O. Colinas1, C. Ruiz McDavitt1, M. Pérez-García1, J. R. López-López1
1. IBGM, Valladolid, Spain.
Hypertension is an important risk factor for cardiovascular diseases and represents the most common cause of death and disability in the Western world. The arterial tone is determined by the contractile state of the vascular smooth muscle cells (VSMCs) in the vessels wall, which is tightly coupled to their resting membrane potential. In fact, membrane depolarization is a common feature of VSMCs in different human and animal models of hypertension1. Resting membrane potential of VSMCs controls Ca2+ influx through voltage-dependent L-type calcium channels (VDCCs), the principal calcium entry pathway in arterial myocytes. An increase in their functional expression has been postulated as an essential element of the hypertension-induced remodelling2. However, the mechanisms involved in the changes in funtional expression of these channels upon hypertension are poorly understood. We have studied VSMCs from mesenteric arteries obtained from a hypertensive inbred mice strain (BPH), and the corresponding normotensive strain (BPN). Animal protocols were approved by the Institutional Care and Use Committee of our Institution. Mice were killed by decapitation after isofluorane anesthesia, and mesensteric VSMCs were obtained by enzymatic dissociation. Real-time PCR and electrophysiological recordings were carried out to examine the expression and function of these channels in VSMCs and their regulation in essential hypertension. RT-PCR analysis reveals mRNA expression of several Cav1 and Cav3 genes in mesenteric VSMCs from BPN mice, with a significant decrease in the expression of Cav1.2 mRNA in BPH. Functional characterization of Cav channels was performed with the whole-cell and the perforated patch configuration of the patch-clamp technique, using nifedipine (10μM) to block Ca2+ channels and BayK 8644 (10μM) to activate them. The current density of the low voltage-activated (L-type) currents was significantly larger in BPN than in BPH cells. Kinetic and pharmacological analyses of the currents indicate that only L-type VDCCs are functionally detected. The same results were obtained in perforated-patch experiments, excluding intracellular mediators. However, the study of vascular tone in pressurized mesenteric arteries of BPN and BPH, showed a hyperreactivity of BPH arteries, suggesting a larger contribution of the Cav1.2 to Ca2+ influx in these arteries. These contradictory results may be reflecting the differential contribution Cav1.2 accessory subunits to their physiological function, a hypothesis supported by our finding of differences in the functional expression of β and α2-δ subunits in the BPH VSMCs.
Where applicable, experiments conform with Society ethical requirements