Abstract
Parathyroid hormone-related protein (PTHrP) released from detrusor smooth muscle (DSM) cells upon bladder distension attenuates spontaneous phasic contractions (SPCs) in DSM and associated afferent firing to facilitate urine storage. Here, we investigate the mechanisms underlying PTHrP-induced inhibition of SPCs, focusing on large-conductance Ca2+-activated K+ channels (BK channels) that play a central role in stabilizing DSM excitability. Perforated patch-clamp techniques were applied to DSM cells of the rat bladder dispersed using collagenase. Isometric tension changes were recorded from DSM strips, while intracellular Ca2+ dynamics were visualized using Cal520 AM -loaded DSM bundles. DSM cells developed spontaneous transient outward potassium currents (STOCs) arising from the opening of BK channels. PTHrP (10 nM) increased the frequency of STOCs without affecting their amplitude at a holding potential of − 30 mV but not − 40 mV. PTHrP enlarged depolarization-induced, BK-mediated outward currents at membrane potentials positive to + 20 mV in a manner sensitive to iberiotoxin (100 nM), the BK channel blocker. The PTHrP-induced increases in BK currents were also prevented by inhibitors of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) (CPA 10 µM), L-type voltage-dependent Ca2+ channel (LVDCC) (nifedipine 3 µM) or adenylyl cyclase (SQ22536 100 µM). PTHrP had no effect on depolarization-induced LVDCC currents. PTHrP suppressed and slowed SPCs in an iberiotoxin (100 nM)-sensitive manner. PTHrP also reduced the number of Ca2+ spikes during each burst of spontaneous Ca2+ transients. In conclusion, PTHrP accelerates STOCs discharge presumably by facilitating SR Ca2+ release which prematurely terminates Ca2+ transient bursts resulting in the attenuation of SPCs.
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Data is available on demand from Professor Hikaru Hashitani in whose laboratory this research was undertaken.
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Acknowledgements
We are grateful to Dr. Shunichi Kajioka (Department of Pharmacy in Fukuoka, International University of Health and Welfare) for his dedicated support in cell isolation and patch-clamp technique. We also thank Dr. Richard Lang (Monash University) for his critical reading of the manuscript
Funding
The present study was supported by Grant-in-Aid for Scientific Research (C) (No. 20K09564) from Japan Society for Promotion of Sciences (JSPS) to HH.
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Conceptualization: HH; methodology: WK, HH; formal analysis and investigation: WK, HH; writing—review and editing: WK, HH.
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Kudo, W., Hashitani, H. PTHrP attenuates spontaneous contractions in detrusor smooth muscle of the rat bladder by activating spontaneous transient outward potassium currents. Pflugers Arch - Eur J Physiol 476, 809–820 (2024). https://doi.org/10.1007/s00424-024-02931-2
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DOI: https://doi.org/10.1007/s00424-024-02931-2