Store-Operated Ca2+ Influx and Expression of TRPC Genes in Mouse Sinoatrial Node

• Published in: Circulation research 2007-06, Vol.100 (11), p.1605-1614
• Main Authors: Ju, Yue-Kun, Chu, Yi, Chaulet, Herve, Lai, Donna, Gervasio, Othon L, Graham, Robert M, Cannell, Mark B, Allen, David G
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Adrenergic beta-Agonists - pharmacology; Animals; Anti-Arrhythmia Agents - pharmacology; Biological and medical sciences; Biological Clocks - drug effects; Biological Clocks - genetics; Biological Clocks - physiology; Calcium - metabolism; Calcium Channel Blockers - pharmacology; Calcium Channels - drug effects; Calcium Channels - genetics; Calcium Channels - metabolism; Calcium Signaling - drug effects; Calcium Signaling - genetics; Calcium Signaling - physiology; Enzyme Inhibitors - pharmacology; Fundamental and applied biological sciences. Psychology; Gene Expression - drug effects; In Vitro Techniques; Male; Mice; Mice, Inbred BALB C; Protein Isoforms - drug effects; Protein Isoforms - genetics; Protein Isoforms - metabolism; RNA, Messenger - biosynthesis; Ryanodine - pharmacology; Sarcoplasmic Reticulum - drug effects; Sarcoplasmic Reticulum - metabolism; Sinoatrial Node - cytology; Sinoatrial Node - drug effects; Sinoatrial Node - metabolism; TRPC Cation Channels - drug effects; TRPC Cation Channels - genetics; TRPC Cation Channels - metabolism; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/CIRCRESAHA.107.152181

Store-operated Ca entry was investigated in isolated mouse sinoatrial nodes (SAN) dissected from right atria and loaded with Ca indicators. Incubation of the SAN in Ca-free solution caused a substantial decrease in resting intracellular Ca concentration ([Ca]i) and stopped pacemaker activity. Reintroduction of Ca in the presence of cyclopiazonic acid (CPA), a sarcoplasmic reticulum Ca pump inhibitor, led to sustained elevation of [Ca]i, a characteristic of store-operated Ca channel (SOCC) activity. Two SOCC antagonists, Gd and SKF-96365, inhibited 72±8% and 65±8% of this Ca influx, respectively. SKF-96365 also reduced the spontaneous pacemaker rate to 27±4% of control in the presence of CPA. Because members of the transient receptor potential canonical (TRPC) gene family may encode SOCCs, we used RT-PCR to examine mRNA expression of the 7 known mammalian TRPC isoforms. Transcripts for TRPC1, 2, 3, 4, 6, and 7, but not TRPC5, were detected. Immunohistochemistry using anti-TRPC1, 3, 4, and 6 antibodies revealed positive labeling in the SAN region and single pacemaker cells. These results indicate that mouse SAN exhibits store-operated Ca activity which may be attributable to TRPC expression, and suggest that SOCCs may be involved in regulating pacemaker firing rate.