Store-operated Ca2+entry in porcine airway smooth muscle

Abstract
Ca2+influx triggered by depletion of sarcoplasmic reticulum (SR) Ca2+stores [mediated via store-operated Ca2+channels (SOCC)] was characterized in enzymatically dissociated porcine airway smooth muscle (ASM) cells. When SR Ca2+was depleted by either 5 μM cyclopiazonic acid or 5 mM caffeine in the absence of extracellular Ca2+, subsequent introduction of extracellular Ca2+further elevated [Ca2+]i. SOCC was insensitive to 1 μM nifedipine- or KCl-induced changes in membrane potential. However, preexposure of cells to 100 nM–1 mM La3+or Ni2+inhibited SOCC. Exposure to ACh increased Ca2+influx both in the presence and absence of a depleted SR. Inhibition of inositol 1,4,5-trisphosphate (IP)-induced SR Ca2+release by 20 μM xestospongin D inhibited SOCC, whereas ACh-induced IP3production by 5 μM U-73122 had no effect. Inhibition of Ca2+release through ryanodine receptors (RyR) by 100 μM ryanodine also prevented Ca2+influx via SOCC. Qualitatively similar characteristics of SOCC-mediated Ca2+influx were observed with cyclopiazonic acid- vs. caffeine-induced SR Ca2+depletion. These data demonstrate that a Ni2+/La3+-sensitive Ca2+influx via SOCC in porcine ASM cells involves SR Ca2+release through both IP3and RyR channels. Additional regulation of Ca2+influx by agonist may be related to a receptor-operated, noncapacitative mechanism.

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