Calcium release-activated calcium influx in cultured human mesangial cells.
Ca2+ influx is a major component of the response of cultured human mesangial cells (HMC) to vasoconstrictors. Activators of phospholipase C such as angiotensin II (Ang II) release Ca2+ from intracellular stores and enhance Ca2+ influx, which in turn is modulated by Na+/Ca2+ exchange. By microfluorometry we studied the mechanisms of Ca2+ entry in resting and stimulated fura-2-loaded monolayers or single HMC. Addition of 1 to 10 mM extracellular Ca2+ to cells equilibrated in Ca(2+)-free media resulted in a rapid, persistent elevation of free cytosolic Ca2+ ([Ca2+]i), from 52 +/- 5 to 113 +/- 18 and 226 +/- 37 nM, respectively. Ca2+ influx was blocked by lanthanum or chelation with EGTA, while it was only partially inhibited by voltage-operated Ca2+ channel (VOC) blockers, such as nifedipine or verapamil. The rise of [Ca2+]i at high external [Ca2+] was not due to a Ca(2+)-sensing mechanism with release of intracellular stored Ca2+, since it was prolonged, and it was not seen in cells maintained in normal 1.25 mM [Ca2+] media. Moreover, it was not abolished by prior depletion of Ca2+ stores with 0.5 microM thapsigargin or 5 microM ionomycin in Ca(2+)-free media, which transiently increased [Ca2+]i (to 281 +/- 39 and 380 +/- 51 nM, respectively). On the contrary, both agents markedly potentiated Ca2+ influx upon addition of 1 to 10 mM [Ca2+]e, (to a maximum of 686 +/- 111 and 633 +/- 150 nM, P < 0.05 vs. control).(ABSTRACT TRUNCATED AT 250 WORDS)
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Division of Nephrology, University of Rome, La Sapienza, Italy.
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Pugliese
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D000804:Angiotensin II / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D002478:Cells, Cultured; D003592:Cytophotometry; D016257:Fura-2; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D015220:Calcium Channels; D013729:Terpenes; D000804:Angiotensin II; D015759:Ionomycin; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2