Store-operated Ca2+ influx and expression of TRPC genes in mouse sinoatrial node.
Store-operated Ca(2+) entry was investigated in isolated mouse sinoatrial nodes (SAN) dissected from right atria and loaded with Ca(2+) indicators. Incubation of the SAN in Ca(2+)-free solution caused a substantial decrease in resting intracellular Ca(2+) concentration ([Ca(2+)](i)) and stopped pacemaker activity. Reintroduction of Ca(2+) in the presence of cyclopiazonic acid (CPA), a sarcoplasmic reticulum Ca(2+) pump inhibitor, led to sustained elevation of [Ca(2+)](i), a characteristic of store-operated Ca(2+) channel (SOCC) activity. Two SOCC antagonists, Gd(3+) and SKF-96365, inhibited 72+/-8% and 65+/-8% of this Ca(2+) 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(2+) activity which may be attributable to TRPC expression, and suggest that SOCCs may be involved in regulating pacemaker firing rate.
Ju
Yue-Kun
YK
School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, NSW, Australia. ju@physiol.usyd.edu.au
Chu
Yi
Y
Chaulet
Herve
H
Lai
Donna
D
Gervasio
Othon L
OL
Graham
Robert M
RM
Cannell
Mark B
MB
Allen
David G
DG
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001683:Biological Clocks / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D020033:Protein Isoforms / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D000318:Adrenergic beta-Agonists; D000889:Anti-Arrhythmia Agents; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D012333:RNA, Messenger; D050052:TRPC Cation Channels; D012433:Ryanodine; D002118:Calcium