The role of PLC-IP3 cascade on 4-aminopyridine (4-AP) contracture in electrically-driven rat atrial and diaphragmatic strips: new evidence by neomycin and heparin

Ozlem Kucukhuseyin,Sumbul Khalid,Cihat Kucukhuseyin,Uteuliyev Yerzhan Sabitaliyevich

doi:10.14715/cmb/2018.64.13.6

Ozlem Kucukhuseyin, Sumbul Khalid + Show 2 more

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https://doi.org/10.14715/cmb/2018.64.13.6

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Abstract

Induction of cardiac contractures by 4-AP in Ca2+-free medium implied the involvement of SR and PLC-IP3 cascade. Thus, the role of PLC-IP3 cascade against contractile actions of 4-AP in electrically-driven rat atrial and diaphragmatic strips were studied both in the presence, and absence of Ca2+ using neomycin, a PLC inhibitor, and heparin, an IP3-R antagonist. 4-AP was applied cumulatively in logarithmically increasing concentrations in the range of 1-16µg/ml, and the preparations were treated with neomycin (400µM) or heparin (400µg/ml) for 3min prior to 4-AP injection. Post-rest potentiation in atrial strips was obtained by interruption of stimulation for 30min. 4-AP caused biphasic alteration in twitch amplitudes, as initially increased up to 16mM and then depressed due to contracture development, which were not affected significantly by neomycin and heparin. Both atrial and denervated diaphragmatic strips challenged to 4-AP in the presence and absence of Ca2+ developed dose dependent contractures which were significantly antagonized both by neomycin and heparin (p<0.05). Post-rest first contractions in controls were found to be reduced by 2min exposure to 4mM 4-AP and augmented by 3min exposure to heparin alone. 4-AP responses in the presence of neomycin and heparin were significantly higher than with those only treated with 4-AP alone and lesser than controls. Because of the fact that 4-AP inducing contracture in Ca2+-free medium, Ca2+ causing contracture should be of SR in origin. Depending on these results, it was concluded that activation of PLC-IP3 cascade by 4-AP is involved in the mediation of contracture and contractile actions of this molecule.

Highlights

Increasing breakthroughs in cellular physiology have helped us to improve our understanding related to circuitry for calcium signaling
Similar results were obtained when atrial strips were exposed to 400 μM neomycin for three min, where twitch amplitude remained unaltered (Figure 2A) and contracture developed beyond 8 mM 4-AP (Figure 2B, Table 1) depressed significantly (p< 0.05)
Control %-contractures with 4-AP were in the order of 26.85±4.72, 110.7±17.24 and 188.73±12.92 at 16, 32 and 64 mM 4-AP which were significantly reduced to 1.52±1.19, 13.9±1.05 and128.6±16.85 by pre-treatment with 400 μg/ml heparin for three min as shown in Figure 1 and 2, and in Table 1, respectively (p< 0.05)

Summary

Introduction

Increasing breakthroughs in cellular physiology have helped us to improve our understanding related to circuitry for calcium signaling. It is being realized that 4-aminopyridine (4-AP) interacts widely with calcium (Ca2+) in lots of excitable tissues. Such interactions with Ca2+ might be mediated by inhibition of K+ channels [1,2], promotion of Ca2+-influx through Ca2+ channels into the effector cells [3,4] or by interaction with intracellular Ca2+ depots [5,6,7]. An identical study by Bhaskar et al, 2008 supports our finding that when the normal medium was replaced by a Ca2+-free solution, spontaneous contractions were fully diminished in accompaniment with a gradually developing dose-dependent contracture [8]

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