Human Isolated Bronchial Smooth Muscle Contains Functional Ryanodine/Caffeine–sensitive Ca-Release Channels

Abstract

Human bronchial smooth muscle (HBSM) contraction is implicated in a variety of respiratory diseases, including asthma. Yet, the presence of an operative calcium-induced calcium release (CICR) mechanism, identified in various smooth muscles, has not been established in HBSM. We therefore studied Ca-releasing mechanisms in HBSM obtained at thoracotomy with special attention to ryanodine-sensitive receptor channels (RyRs). In freshly isolated bronchial myocytes, ryanodine (0.5 to 50 microM) and caffeine (1 to 25 mM) induced transient increases in the cytoplasmic calcium concentration ([Ca(2+)](i)). Higher ryanodine concentrations (> 100 microM) inhibited the caffeine-induced [Ca(2+)](i) response, which was also blocked in the presence of tetracaine (300 microM) or ruthenium red (200 microM), two potent CICR inhibitors. In HBSM strips, caffeine induced a transient contraction which, likewise, was inhibited by ryanodine and tetracaine. However, ryanodine (200 microM) modified neither the [Ca(2+)](i) response nor the contraction induced by K(+)-rich (110 mM) solution. Reverse transcriptase/polymerase chain reaction (RT-PCR) and RNase protection assay performed in HBSM have revealed the existence of mRNAs encoding only the type 3 RyR. We also characterized acetylcholine-induced [Ca(2+)](i) and contractile responses. None of these responses was altered by ryanodine or by tetracaine. These results demonstrate, for the first time, the existence of functional RyRs in HBSM cells which, owing to the type of isoform or the amount of protein expressed, are not involved, under physiologic conditions, in depolarization- or agonist-induced contraction.

Expression and coupling of neurokinin receptor subtypes to inositol phosphate and calcium signaling pathways in human airway smooth muscle cells

“…The effect of caffeine on the initial phase can be attributed to a partial depletion of SR stores by the preexposure to caffeine. However, it has been reported that acetylcholine-induced [Ca 2ϩ ] i increase in human bronchial smooth muscle cell was not impaired by ryanodine (22). Together, these results suggest that ryanodine receptors expressed in HASM cells do not have a significant role in the initial transient phase of NKR-mediated increases in [Ca 2ϩ ] i .…”

“…In contrast, caffeine but not ryanodine inhibited the transient [Ca 2ϩ ] i increase induced by NKR-selective agonists. Hyvelin et al (22) reported that only ryr3 mRNA was expressed in human bronchial smooth muscle cells. The function of the type 3 ryanodine receptor is still poorly understood, whereas type 1 and type 2 ryanodine receptors have been clearly implicated in excitationcontraction coupling in skeletal and cardiac muscle (18).…”

Calcium Signaling in Airway Smooth Muscle

“…Airway smooth muscle cells from different species express all three isoforms of the ryanodine receptors, although RyR2 and RyR3 appear to be the predominant isoforms (22,24). Calcium release from the SR through RyR is an important component of the intracellular calcium response after activation of G proteincoupled receptors (GPCRs) in ASM cells.…”

Identification of estradiol/ERα-regulated genes in the mouse pituitary

“…Interestingly, in the case of r-Kurtoxin, treatment with the lower concentration of the Ca v 3.1-associated channel blocker provided the reduction in the priming effect, while the higher concentration did not show this effect. However, it is often seen in studies that with increasing concentrations of the administered molecule, the observed effects plateau off and sometimes reverse at higher concentrations as the binding sites or receptors become saturated and oversaturated (Trotta et al 1980, Hyvelin et al 2000. Although more detailed experiments will be required to verify their supposed electro-physiological roles in regulation of LH secretion by GnRH, these initial findings lay the groundwork for the involvement of all three channels in regulating LH secretion.…”