Properties of a Native Cation Channel Activated by Ca2+ Store Depletion in Vascular Smooth Muscle Cells

• Published in: The Journal of biological chemistry Vol. 276; no. 11; pp. 7782 - 7790
• Main Authors: Trepakova, Elena S., Gericke, Marion, Hirakawa, Yoji, Weisbrod, Robert M., Cohen, Richard A., Bolotina, Victoria M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.03.2001; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Aorta - drug effects; Aorta - metabolism; Calcium - metabolism; Cells, Cultured; Dogs; Egtazic Acid - analogs & derivatives; Egtazic Acid - pharmacology; Ion Channels - physiology; Mice; Mice, Inbred C57BL; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - metabolism; Rabbits; Thapsigargin - pharmacology; Vasoconstriction - drug effects
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M010104200

Depletion of intracellular Ca2+ stores activates capacitative Ca2+influx in smooth muscle cells, but the native store-operated channels that mediate such influx remain unidentified. Recently we demonstrated that calcium influx factor produced by yeast and human platelets with depleted Ca2+ stores activates small conductance cation channels in excised membrane patches from vascular smooth muscle cells (SMC). Here we characterize these channels in intact cells and present evidence that they belong to the class of store-operated channels, which are activated upon passive depletion of Ca2+ stores. Application of thapsigargin (TG), an inhibitor of sarco-endoplasmic reticulum Ca2+ ATPase, to individual SMC activated single 3-pS cation channels in cell-attached membrane patches. Channels remained active when inside-out membrane patches were excised from the cells. Excision of membrane patches from resting SMC did not by itself activate the channels. Load-ing SMC with BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid), which slowly depletes Ca2+ stores without a rise in intracellular Ca2+, activated the same 3-pS channels in cell-attached membrane patches as well as whole cell nonselective cation currents in SMC. TG- and BAPTA-activated 3-pS channels were cation-selective but poorly discriminated among Ca2+, Sr2+, Ba2+, Na+, K+, and Cs+. Open channel probability did not change at negative membrane potentials but increased significantly at high positive potentials. Activation of 3-pS channels did not depend on intracellular Ca2+ concentration. Neither TG nor a variety of second messengers (including Ca2+, InsP3, InsP4, GTPγS, cyclic AMP, cyclic GMP, ATP, and ADP) activated 3-pS channels in inside-out membrane patches. Thus, 3-pS nonselective cation channels are present and activated by TG or BAPTA-induced depletion of intracellular Ca2+ stores in intact SMC. These native store-operated cation channels can account for capacitative Ca2+ influx in SMC and can play an important role in regulation of vascular tone.