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Properties of spontaneous depolarizations in circular smooth muscle cells of rabbit urethra
Author(s) -
Hashitani Hikaru,
Helden Dirk F.,
Suzuki Hikaru
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15584.x
Subject(s) - niflumic acid , cyclopiazonic acid , biophysics , dids , depolarization , tetrodotoxin , phentolamine , guanethidine , chemistry , hyperpolarization (physics) , membrane potential , intracellular , procaine , channel blocker , endocrinology , medicine , anatomy , biology , pharmacology , stereochemistry , biochemistry , calcium , stimulation , membrane , nuclear magnetic resonance spectroscopy
1 . Intracellular microelectrode recordings were made from circular smooth muscle of rabbit urethra. 2 . The smooth muscle of urethra was spontaneously active exhibiting large, regularly occurring depolarizations, termed slow waves (SWs), 1–3 s in duration, up to 40 mV in amplitude and generated every 3–15 s and small irregularly occurring events (or summations there of) termed spontaneous transient depolarizations (STDs) of < 1 s in duration. 3 . The SWs and STDs were not sensitive to 10 −6 m atropine, 10 −6 m phentolamine, 10 −5 m guanethidine or 10 −6 m tetrodotoxin, indicating that they were myogenic in origin. 4 . Application of 3 × 10 −6 m nifedipine or 5 × 10 −5 m GdCl 3 did not inhibit the generation of SWs or STDs, indicating that activation of L‐type Ca 2+ channels and non‐selective cation channels are not essential for their generation. However, the duration of SWs but not STDs was reduced by nifedipine, indicating L‐type Ca 2+ channels contribute to the plateau‐like potential of SWs. 5 . Application of low chloride solution (6.4 mM), niflumic acid (10 −5 ‐10 −4 m ) or 4,4′‐diisothiocyanostilbene‐2,2′‐disulphonic acid (DIDS, 10 −4 ‐5 × 10 −4 m ) inhibited the generation of SWs and STDs, suggesting an involvement of chloride channels. 6 . Application of nominally Ca 2+ free solution, 5 × 10 −5 m BAPTA‐AM, 10 −5 m cyclopiazonic acid, 10 −2 m caffeine or 10 −3 m procaine inhibited the generation of SWs and STDs, indicating that Ca 2+ released from intracellular stores was required for the generation of SWs and STDs. 7 . Exogenously applied noradrenaline (10 −7 ‐10 −5 m ) increased the frequency of SWs through stimulation of α‐adrenoceptors which was inhibited by sodium nitroprusside (SNP, 10 −4 m ). SNP also reduced the frequency of SWs without altering the membrane potential, an effect mimicked by 8‐bromocyclic GMP (10 −3 m ) indicating that SNP acted by elevating the production of cyclic GMP. 8 . It is concluded that smooth muscle cells of the rabbit urethra exhibit SWs and STDs which are likely to be induced by stimulation of Ca 2+ ‐activated chloride channels evoked by release of Ca 2+ from intracellular stores.