Store-refilling involves both L-type calcium channels and reverse-mode sodium–calcium exchange in airway smooth muscle

Abstract

The aim of the present study was to examine the relative contributions to storerefilling of the two following voltage-regulated calcium ion influx pathways: 1) L-type-Ca 2+ channels; and 2) the reverse-mode of the sodium-calcium exchanger (NCX).Successive acetylcholine-induced contractions, triggered in bovine tracheal smooth muscle strips, were measured to determine the effect of intervention on contractions as an indication of the extent of store-refilling.Pre-treating the tissues with cromakalim significantly reduced the magnitude of successive contractions. Zero-Ca 2+ bathing media abolished the contractions, an effect that was completely reversed upon reintroduction of Ca 2+. Inhibition of L-type Ca 2+ channels, with nifedipine, significantly reduced the magnitude of the contractions. Similarly, inhibition of the reverse-mode of the NCX, with KB-R7943, significantly reduced the magnitude of the contractions. However, neither nifedipine nor KB-R7943 alone reduced contractions to the same extent as observed under zero-Ca 2+ conditions. Concurrent treatment with nifedipine and KB-R7943 almost abolished successive contractions. Furthermore, concurrent treatment with nifedipine and zero-Na + bathing media displayed a significantly greater effect than nifedipine alone. Probing the expression of NCX1 isoforms by Western blotting revealed the presence of three bands of 160, 120 and 110 kDa. The 120-and 110-kDa bands were identified as variably spliced NCX isoforms, NCX1.1 and NCX1.3, respectively. Taken together, these data suggest that influx of calcium ions through both L-type calcium channels and the reverse-mode of the sodium-calcium exchanger is necessary for complete store-refilling in airway smooth muscle.

Effects of Ginger and Its Constituents on Airway Smooth Muscle Relaxation and Calcium Regulation

“…Increases in [Ca 21 ] i in ASM after bronchoconstrictor stimulation are attributed to calcium depletion from the SR, as well as calcium influx through the plasma membrane (18,33). Calcium influx can occur through voltage-gated (34) and receptoroperated (35) channels, the sodium-calcium exchanger (reverse mode) (36,37), store-operated calcium entry channels (38)(39)(40), and transient receptor potential (TRP) channels (41)(42)(43). Both TRPC and TRPV channels have gained attention for modulating calcium influx in ASM (41,44), whereas TRPV1 antagonists relax human small airways (24).…”

Cellular Ca2+ Dynamics in Urinary Bladder Smooth Muscle From Transgenic Mice Overexpressing Na+-Ca2+ Exchanger

“…The findings suggesting that NCX functions in the reverse mode under physiological conditions have been accumulating (13,14). Under pathophysiological conditions, the up-regulation of NCX and its accelerated functions in reverse mode has been also reported (6,15).…”

The Role of Sodium-Calcium Exchanger in the Calcium Homeostasis of Airway Smooth Muscle

“…At the protein level, NCX1 expression was demonstrated in bovine tracheal smooth muscle, where apparently a 120 kDa and a 110 kDa proteins corresponding to NCX1.1 and NCX1.3 isoforms, respectively, were identified by Western blotting [85]. Functional and comparative studies of the major NCX1.1 and the NCX1.3 isoforms have shown aminoacid differences within these variable exons that influence the inhibitory sensitivity de NCX to intracellular Na + (77)(78)(79).…”