Fendiline increases [Ca2+]i in Madin Darby canine kidney (MDCK) cells by releasing internal Ca2+ followed by capacitative Ca2+ entry.
The effect of fendiline, a documented inhibitor of L-type Ca2+ channels and calmodulin, on Ca2+ signaling in Madin Darby canine kidney (MDCK) cells was investigated using fura-2 as a Ca2+ probe. Fendiline at 5-100 microM significantly increased [Ca2+]i concentration-dependently. The [Ca2+]i rise consisted of an initial rise and a slow decay. External Ca2+ removal partly inhibited the Ca2+ signals induced by 25-100 microM fendiline by reducing both the initial rise and the decay phase. This suggests that fendiline triggered external Ca2+ influx and internal Ca2+ release. In Ca(2+)-free medium, pretreatment with 50 microM fendiline nearly abolished the [Ca2+]i rise induced by 1 microM thapsigargin, an endoplasmic reticulum Ca2+ pump inhibitor, and vice versa, pretreatment with thapsigargin prevented fendiline from releasing internal Ca2+. This indicates that the internal Ca2+ source for fendiline overlaps with that for thapsigargin. At a concentration of 50 microM, fendiline caused Mn2+ quench of fura-2 fluorescence at the 360 nm excitation wavelenghth, which was inhibited by 0.1 mM La3+ by 50%, implying that fendiline-induced Ca2+ influx has two components separable by La3+. Consistently, 0.1 mM La3+ pretreatment suppressed fendiline-induced [Ca2+]i rise, and adding La3+ during the rising phase immediately inhibited the signal. Addition of 3 mM Ca2+ increased [Ca2+]i after preincubation with 50-100 microM fendiline in Ca(2+)-free medium. However, 50-100 microM fendiline inhibited 1 microM thapsigargin-induced capacitative Ca2+ entry. Pretreatment with 40 microM aristolochic acid to inhibit phospholipase A2 inhibited 50 microM fendiline-induced internal Ca2+ release by 48%, but inhibition of phospholipase C with 2 microM U73122 or inhibition of phospholipase D with 0.1 mM propranolol had no effect. Collectively, we have found that fendiline increased [Ca2+]i in MDCK cells by releasing internal Ca2+ in a manner independent of inositol-1,4,5-trisphosphate (IP3), followed by external Ca2+ influx.
Jan
C R
CR
Department of Medical Education and Research, Veterans General Hospital-Kaohsiung, Taiwan. crjan@isca.vghks.gov.tw
Tseng
C J
CJ
Chen
W C
WC
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002460:Cell Line; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005275:Fendiline / Q000494:pharmacology*; D017136:Ion Transport; D007668:Kidney / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010740:Phospholipases / Q000037:antagonists & inhibitors; D019284:Thapsigargin / Q000037:antagonists & inhibitors / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D019284:Thapsigargin; D010740:Phospholipases; D005275:Fendiline; D002118:Calcium