Characteristics of a store-operated calcium-permeable channel: sarcoendoplasmic reticulum calcium pump function controls channel gating.
We examined the single channel properties and regulation of store-operated calcium channels (SOCC). In human submandibular gland cells, carbachol (CCh) induced flickery channel activity while thapsigargin (Tg) induced burst-like activity, with relatively lower open probability (NP(o)) and longer mean open time. Tg- and CCh-activated channels were permeable to Na(+) and Ba(2+), but not to NMDG, in the absence of Ca(2+). The channels exhibited similar Ca(2+), Na(+), and Ba(2+) conductances and were inhibited by 2-aminoethoxydiphenylborate, xestospongin C, Gd(3+), and La(3+). CCh stimulated flickery activity changed to burst-like activity by (i) addition of Tg, (ii) using Na(+) instead of Ca(2+), (iii) using Ca(2+)-free bath solution, or (iv) buffering [Ca(2+)](i) with BAPTA-AM. Buffering [Ca(2+)](i) induced a 2-fold increase in NP(o) of Tg-stimulated SOCC. Reducing free [Ca(2+)] in the endoplasmic reticulum with the divalent cation chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), induced burst-like channel activity similar to that seen with CCh + Tg. Thus, SOCC is activated by stimulation of muscarinic receptors, inhibition of the sarcoendoplasmic Ca(2+) pump, and lowering [Ca(2+)] in the internal store. Importantly, SOCC activity depends on [Ca(2+)](i) and the free [Ca(2+)] in the internal store. These novel findings reveal that SERCA plays a major role in the gating of SOCC by (i) refilling the internal Ca(2+) store(s) and (ii) decreasing the [Ca(2+)](i)-dependent inhibition.
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Secretory Physiology Section, GTTB, NIDCR, National Institutes of Health, Bethesda, Maryland 20892, USA.
Ambudkar
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D001464:Barium / Q000378:metabolism; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000737:chemistry*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D002460:Cell Line; D018679:Cholinergic Agonists / Q000494:pharmacology; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005029:Ethylenediamines / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology; D005990:Glycerol / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D047028:Macrocyclic Compounds; D010080:Oxazoles / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology
D001896:Boron Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002412:Cations; D018679:Cholinergic Agonists; D004791:Enzyme Inhibitors; D005029:Ethylenediamines; D047028:Macrocyclic Compounds; D010080:Oxazoles; C108644:xestospongin A; D001464:Barium; D019284:Thapsigargin; D002217:Carbachol; D012964:Sodium; D005682:Gadolinium; C109986:2-aminoethoxydiphenyl borate; D000252:Calcium-Transporting ATPases; D005990:Glycerol; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine; D002118:Calcium