Activation of non-selective cation conductance by carbachol in freshly isolated bovine ciliary muscle cells

Takai, Yoshiko; Awaya, S; Takai, Akira

doi:10.1007/s004240050335

“…The reversal potential (Vrev) of ICCh suggested that the CChactivated non-selective cation channel is twice as permeable for Ca¥ than for Cs¤ ions (see also Takai et al 1997), similar to the value reported for the P2x-gated non-selective cation channels (Benham & Tsien, 1987;Benham, 1989;Fieber & Adams, 1991;Schneider et al 1991). When we extrapolated this result from bi-ionic 110 mÒ Ca¥-140 mÒ Cs¤ conditions to more physiological Cs¤ Tyrode solution (eqn (7)) we obtained *fCa = 0·14.…”

Section: Discussionsupporting

confidence: 54%

“…7B). The reversal potential was 19·5 ± 0·77 mV (n = 11), a value similar to the one obtained for the ACh-activated non-selective cationic current in other smooth muscle cells (Inoue & Isenberg, 1991a;Takai et al 1997). According to eqn (6), Vrev = 20 mV translates into a permeability ratio of 2:1.…”

Section: Electrophysiological Estimation Of the Ca¥ Permeability Ratiomentioning

confidence: 50%

“…Although previous reports in intestinal myocytes have shown a close relationship between the amplitude of ICCh and Ä [Ca¥]c (Pacaud & Bolton, 1991;Komori et al 1993), direct demonstration of Ca¥ influx through NSCCCh causing Ä [Ca¥]c is still missing. In extracellular 90 mÒ CaClµ solutions, inward ICCh was measured, suggesting the existence of tonic Ca¥ influx, and from its reversal potential (ca +20 mV) a permeability ratio of Ca¥ versus monovalent cations of ca 2:1 was extrapolated (Inoue & Isenberg, 1990a;Takai et al 1997).…”

mentioning

confidence: 99%

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Ca²⁺ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes

Kim

¹

,

Koh

²

,

Kang

³

et al. 1998

The Journal of Physiology

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Ca2+ microfluorometry (100 μm K5 fura‐2) and the voltage‐clamp technique were combined to study the effect of carbachol (CCh, 50 μm) in inducing currents (ICCh) through non‐selective cation channels (NSCCCh) and increments in global cytosolic Ca2+ concentration (Δ[Ca2+]c). In Na+‐containing bath solution, ICCh fell from an initial phasic to a subsequent small (5 %) tonic component; Δ[Ca2+]c fell to zero. Tonic ICCh and [Ca2+]c became prominent after substitution of extracellular 140 mm Na+ by 140 mm Cs+. Tonic ICCh and Δ[Ca2+]c were insensitive to intracellular heparin (3 mg ml−1) and ryanodine (4 μm), i.e. they did not depend on Ca2+ release from sarcoplasmic reticulum (SR). Single channel currents of NSCCCh could be resolved in whole‐cell recordings. Substitution of Na+ by Cs+ increased NSCCCh activity by one order of magnitude and slope conductance from 22 to 30 pS. Extracellular quinidine (3 μm) reversibly blocked the NSCCCh activity. Both tonic ICCh and tonic Δ[Ca2+]c (a) followed a similar time course of activation, desensitization and facilitation, (b) were reversibly blocked by 3 μm quinidine, and (c) persisted upon block of SR Ca2+ release. A Ca2+ fractional current of tonic ICCh (fCa) of 0.009 was calculated by comparing the ratio Δ[Ca2+]c (corrected for simultaneous Ca2+ redistribution) over ICCh with depolarization‐induced *Δ[Ca2+]c (Δ[Ca2+]c calculated from ICa induced by a 400 ms depolarization from −60 to 0 mV at 2 mm[Ca2+]o, 145 mm[Cs+]o) over ICa. fCa was 0.023 at [Ca2+]o= 4 mm. With 110 mm extracellular CaCl2 and 145 mm intracellular CsCl, ICCh reversed at +19.5 mV suggesting a permeability ratio PCa/PCs of 2.8. We conclude that Ca2+ influx through NSCCCh under physiological [Ca2+]o could induce Δ[Ca2+]c. The fCa was, however, much smaller than the one calculated from the reversal potential.

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“…The transient inward component studied in the present paper is rather unique in its selectivity for Ca 2+ , although muscarinic receptor activated cation channels permeable to Ca 2+ have been observed in other preparations (Takai et al 1997). We suggest that the cation current could play a role in maintenance of the cell's ability to contract after repeated stimulations.…”

Section: Discussionmentioning

confidence: 48%

Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

Molleman

¹

,

Liu²,

Huizinga³

2001

Rev. can. physiol. pharmacol.

0

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Muscarinic receptor mediated membrane currents and contractions were studied in isolated canine colon circular smooth muscle cells. Carbachol (10 -5 M) evoked a slow transient inward current that was superimposed by a transient outward current at holding potentials greater than -50 mV. Carbachol contracted the cells by 70 ± 2%. The effects of carbachol were blocked by atropine (10 -6 M), tetraethyl ammonium (20 mM), and BAPTA-AM (25 mM applied for 20 min). The inward current and contraction were not sensitive to diltiazem (10 -5 M), nitrendipine (3 × 10 -7 M), niflumic acid (10 -5 M), or N-phenylanthranilic acid (10 -4 M), but were gradually inhibited after repetitive stimulations in Ca 2+ free solution. Ni 2+ (2 mM) inhibited the inward current by 67 ± 4%. The inward current reversed at +15 mV. The outward component could be selectively inhibited by iberiotoxin (20 nM) or by intracellular Cs + . Repeated stimulation in the presence of cyclopiazonic acid (CPA, 3 µM) inhibited the carbachol-induced outward current and partially inhibited contraction. CPA did not inhibit the inward current. In conclusion, muscarinic receptor stimulation evoked a CPA-sensitive calcium release that caused contraction and a CPA-insensitive transient inward current was activated that is primarily carried by Ca 2+ ions and is sensitive to Ni 2+ .Key words: calcium, carbachol, smooth muscle, cyclopiazonic acid, sarcoplasmic reticulum.Résumé : On a examiné la contraction et les courants membranaires induits par les récepteurs muscariniques dans des cellules musculaires lisses circulaires isolées de côlons canins. Le carbachol (10 -5 M) a induit un courant entrant transitoire lent auquel s'est ajouté un courant sortant transitoire aux potentiels de maintien supérieurs à -50 mV. Le carbachol a contracté les cellules à 70 ± 2 %. Ses effets ont été bloqués par l'atropine (10 -6 M), le tétraéthy-lammonium (20 mM) et le BAPTA-AM (25 mM appliqué pendant 20 min). Le courant entrant et la contraction ont été insensibles au diltiazem (10 -5 M), à la nitrendipine (3 × 10 -7 M), à l'acide niflumique (10 -5 M) ou à l'acide N-phénylanthranilique (10 -4 M), mais ils ont été graduellement inhibés après des stimulations répétées dans une solution sans Ca 2+ . Le Ni 2+ (2 mM) a inhibé le courant entrant de 76 ± 4 %. Celui-ci a été inversé à +15 mV. Le courant sortant a pu être sélectivement inhibé par l'ibériotoxine (20 nM) ou par le Cs + intracellulaire. Une stimulation répétée en présence d'acide cyclopiazonique (CPA, 3 µM) a inhibé le courant sortant induit par le carbachol, et partiellement inhibé la contraction, mais n'a pas inhibé le courant entrant. Ainsi, la stimulation des récepteurs muscariniques provoque une libération de calcium sensible au CPA qui déclenche la contraction. De plus, un courant entrant transitoire insensible au CPA, principalement transporté par les ions Ca 2+ et sensible au Ni 2+ , est activé.

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“…The sustained component is mediated by a non-selective cation channel that does not discriminate between Ca 2+ and Na + (Lee et al 1993). Muscarinic receptor mediated cation channels that are permeable to Ca 2+ are also found in bovine ciliary muscle cells (Takai et al 1997). It is likely that both the transient and the sustained components of the inward current contribute to the contraction along with the depolarization associated with muscarinic stimulation.…”

Section: Carbachol-induced Transient Inward Currentmentioning

confidence: 99%

Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

Molleman¹,

Liu²,

Huizinga³

2001

Can. J. Physiol. Pharmacol.

0

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Muscarinic receptor mediated membrane currents and contractions were studied in isolated canine colon circular smooth muscle cells. Carbachol (10 -5 M) evoked a slow transient inward current that was superimposed by a transient outward current at holding potentials greater than -50 mV. Carbachol contracted the cells by 70 ± 2%. The effects of carbachol were blocked by atropine (10 -6 M), tetraethyl ammonium (20 mM), and BAPTA-AM (25 mM applied for 20 min). The inward current and contraction were not sensitive to diltiazem (10 -5 M), nitrendipine (3 × 10 -7 M), niflumic acid (10 -5 M), or N-phenylanthranilic acid (10 -4 M), but were gradually inhibited after repetitive stimulations in Ca 2+ free solution. Ni 2+ (2 mM) inhibited the inward current by 67 ± 4%. The inward current reversed at +15 mV. The outward component could be selectively inhibited by iberiotoxin (20 nM) or by intracellular Cs + . Repeated stimulation in the presence of cyclopiazonic acid (CPA, 3 µM) inhibited the carbachol-induced outward current and partially inhibited contraction. CPA did not inhibit the inward current. In conclusion, muscarinic receptor stimulation evoked a CPA-sensitive calcium release that caused contraction and a CPA-insensitive transient inward current was activated that is primarily carried by Ca 2+ ions and is sensitive to Ni 2+ .Key words: calcium, carbachol, smooth muscle, cyclopiazonic acid, sarcoplasmic reticulum.Résumé : On a examiné la contraction et les courants membranaires induits par les récepteurs muscariniques dans des cellules musculaires lisses circulaires isolées de côlons canins. Le carbachol (10 -5 M) a induit un courant entrant transitoire lent auquel s'est ajouté un courant sortant transitoire aux potentiels de maintien supérieurs à -50 mV. Le carbachol a contracté les cellules à 70 ± 2 %. Ses effets ont été bloqués par l'atropine (10 -6 M), le tétraéthy-lammonium (20 mM) et le BAPTA-AM (25 mM appliqué pendant 20 min). Le courant entrant et la contraction ont été insensibles au diltiazem (10 -5 M), à la nitrendipine (3 × 10 -7 M), à l'acide niflumique (10 -5 M) ou à l'acide N-phénylanthranilique (10 -4 M), mais ils ont été graduellement inhibés après des stimulations répétées dans une solution sans Ca 2+ . Le Ni 2+ (2 mM) a inhibé le courant entrant de 76 ± 4 %. Celui-ci a été inversé à +15 mV. Le courant sortant a pu être sélectivement inhibé par l'ibériotoxine (20 nM) ou par le Cs + intracellulaire. Une stimulation répétée en présence d'acide cyclopiazonique (CPA, 3 µM) a inhibé le courant sortant induit par le carbachol, et partiellement inhibé la contraction, mais n'a pas inhibé le courant entrant. Ainsi, la stimulation des récepteurs muscariniques provoque une libération de calcium sensible au CPA qui déclenche la contraction. De plus, un courant entrant transitoire insensible au CPA, principalement transporté par les ions Ca 2+ et sensible au Ni 2+ , est activé.

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Activation of non-selective cation conductance by carbachol in freshly isolated bovine ciliary muscle cells

Cited by 14 publications

References 31 publications

Ca²⁺ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes

Ca²⁺ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes

Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

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Activation of non-selective cation conductance by carbachol in freshly isolated bovine ciliary muscle cells

Cited by 14 publications

References 31 publications

Ca2+ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes

Ca2+ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes

Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

Muscarinic activation of transient inward current and contraction in canine colon circular smooth muscle cells

Contact Info

Product

Resources

About

Ca²⁺ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes

Ca²⁺ influx through carbachol‐activated non‐selective cation channels in guinea‐pig gastric myocytes