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

Abstract

Depletion of intracellular Ca2؉ stores activates capacitative Ca 2؉ influx in smooth muscle cells, but the native storeoperated channels that mediate such influx remain unidentified. Recently we demonstrated that calcium influx factor produced by yeast and human platelets with depleted Ca 2؉ 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 storeoperated channels, which are activated upon passive depletion of Ca 2؉ stores. Application of thapsigargin (TG), an inhibitor of sarco-endoplasmic reticulum Ca 2؉ 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 Ca 2؉ stores without a rise in intracellular Ca (4, 8) and certain members of the diverse family of TRP channels (9, 10) are thought to be responsible for CCE. However, to date the existence of neither of those has been established in SMC. Importantly, depletion of Ca 2ϩ stores was shown to trigger not only Ca 2ϩ , but also Na ϩ influx in arterial myocytes (11), which implies that store-operated channels in SMC are poorly selective for cations. In freshly isolated mouse anococcygeus SMC there are strong indications that CCE results from activation of a whole cell nonselective cation current (12, 13), although in rat aortic SMC line A7r5 no currents were detected which could be associated with CCE (14, 15). It is totally unclear if the same or different storeoperated channels mediate CCE in SMC from different preparations.Here for the first time we characterize 3-pS cation channels that are activated by Ca 2ϩ store depletion in intact SMC from mouse and rabbit aorta. These channels, contrary to highly Ca 2ϩ -selective CRAC channels, are poorly selective for monoand divalent cations, and under physiological conditions they will allow both Ca 2ϩ and Na ϩ to enter SMC. Recently we found that these channels can also be activated in excised membrane patches by calcium influx factor (CIF) partially purified from human platelets or yeast with depleted Ca 2ϩ stores (16). Taken together, these data strongly support the idea that the native 3-pS channels, which we found in SMC, belong to the class of store-operated ion channels. Preliminary data have been reported in abstract form (17, 18). EXPERIMENTAL PROCEDURES SMC PreparationFour different preparations of aortic SMC were used in our experiments, and the 3-pS channel described in this paper was found to be the same in acutely dispersed and cultured SMC from mouse and rabbit aorta. Most of the experiments on characterization of the single channels and whole cell currents were done on mSMC in short term culture because they pr...

Human Trp3 forms both inositol trisphosphate receptor-dependent and receptor-independent store-operated cation channels in DT40 avian B lymphocytes

“…A clear alternative is the suggested diffusible messenger for CCE, termed calcium inf lux factor (9,10). Interestingly, there is recent evidence for such a mode of signaling in vascular smooth muscle cells (48), which is one of the cell types that expresses the nonselective cation channel version of CCE (18).…”

“…In other cell types, currents have been observed that have moderate divalent cation selectivity (12,13), and there are a number of examples of store-operated, nonselective cation currents (14)(15)(16)(17)(18).…”

Ca2+-independent Phospholipase A2 Is a Novel Determinant of Store-operated Ca2+ Entry

“…Cells-Primary culture SMC from mouse (mSMC) and rabbit (rSMC) aorta were prepared as described previously (10,25). Human platelets were prepared from the platelet-rich plasma as described previously (26).…”

“…9). Second, nonselective SOC channels of small, but resolvable 3 pS conductance has been found and described on single channel and whole-cell current levels by us (10,11) and by others (12)(13)(14)(15)(16)(17)(18) in vascular SMC and human platelets. Despite a great physiological importance of both types of SOC channels, the molecular mechanism of their activation is still unresolved.…”

Properties of a store-operated nonselective cation channel in airway smooth muscle

“…As such, the current finding that an ,25 pS channel underlies CPA-and BAPTA-AM-evoked NSCC currents in bovine TSMs is novel. The magnitude of the conductance described herein is 10-fold greater than that reported for store depletion-activated NSCCs in vascular smooth muscle cells [25,30,31]; the possibility that small conductance NSCCs were hidden within the noise inherent in the recordings cannot be ruled out. Involvement of this NSCC explains why the Ca 2+ entry induced by CPA was resistant to nifedipine ( fig.…”