Effect of gallopamil on excitation-contraction coupling

Airway remodeling in asthma: new mechanisms and potential for pharmacological intervention

The chronic inflammatory response within the airways of asthmatics is associated with structural changes termed airway remodeling. This remodeling process is a key feature of severe asthma. The 5-10% of patients with a severe form of the disease account for the higher morbidity and health costs related to asthma. Among the histopathological characteristics of airway remodeling, recent reports indicate that the increased mass of airway smooth muscle (ASM) plays a critical role. ASM cell proliferation in severe asthma implicates a gallopamil-sensitive calcium influx and the activation of calcium-calmodulin kinase IV leading to enhanced mitochondrial biogenesis through the activation of various transcription factors (PGC-1α, NRF-1 and mt-TFA). The altered expression and function of sarco/endoplasmic reticulum Ca(2+) pump could play a role in ASM remodeling in moderate to severe asthma. Additionally, aberrant communication between an injured airway epithelium and ASM could also contribute to disease severity. Airway remodeling is insensitive to corticosteroids and anti-leukotrienes whereas the effect of monoclonal antibodies (the anti-IgE omalizumab, the anti-interleukin-5 mepolizumab or anti-tumor necrosis factor-alpha) remains to be investigated. This review focuses on potential new therapeutic strategies targeting ASM cells, especially Ca(2+) and mitochondria-dependent pathways.

Effects of diltiazem or verapamil on calcium uptake and release from chicken skeletal muscle sarcoplasmic reticulum

The purpose of this study was to determine the effects of 2 Ca2+ channel blockers, verapamil and diltiazem, on calcium loading (active Ca2+ uptake) and the following Ca2+ release induced by silver ion (Ag+) and Ca2+ from the membrane of heavy sarcoplasmic reticulum (SR) of chicken skeletal muscle. A fluorescent probe technique was employed to determine the calcium movement through the SR. Pretreatment of the medium with diltiazem and verapamil resulted in a significant decrease in the active Ca2+ uptake, with IC50 of about 290 micromol/L for verapamil and 260 micromol/L for diltiazem. Inhibition of Ca2+ uptake was not due to the development of a substantial drug-dependent leak of Ca2+ from the SR. It might, in part, have been mediated by a direct inhibitory effect of these drugs on the Ca2+ ATPase activity of the SR Ca2+ pump. We confirmed that Ca2+ channel blockers, administered after SR Ca2+ loading and before induction of Ca2+ release, caused a dose-dependent inhibition of both Ca2+- and Ag+-induced Ca2+ release rate. Moreover, if Ca2+ channel blockers were administered prior to SR Ca2+ loading, in spite of Ca2+ uptake inhibition the same reduction in Ca2+- and Ag+-induced Ca2+ release rate was seen. We showed that the inhibition of Ag+-induced Ca2+ release by L-channel blockers is more sensitive than Ca2+-induced Ca2+ release inhibition, so the IC50 for Ag+- and Ca2+-induced Ca2+ release was about 100 and 310 micromol/L for verapamil and 79 and 330 micromol/L for diltiazem, respectively. Our results support the evidence that Ca2+ channel blockers affect muscle microsome of chicken skeletal muscle by 2 independent mechanisms: first, reduction of Ca2+ uptake rate and Ca2+-ATPase activity inhibition, and second, inhibition of both Ag+- and Ca2+-induced Ca2+ release by Ca2+ release channels. These findings confirm the direct effect of Ca2+ channel blockers on calcium release channels. Our results suggest that even if the SR is incompletely preloaded with Ca2+ because of inhibition of Ca2+ uptake by verapamil and diltiazem, no impairment in Ca2+ release occurs.