Properties of chloride transport in barnacle muscle fibers.

SUMMARY1. Cl movements across the cell membranes of smoth muscle from the guinea-pig vas deferens were measured using Cl-sensitive micro-electrodes and 36C1 fluxes. The rate constants for the loss of Cl ions measured by both methods under a variety of conditions were used to calculate the apparent Cl permeability (PC1).2. If it is assumed that the initial rate of decline of the intracellular Cl activity (a 1) on removal of extracellular Cl (ClO) represents net transmembrane Cl movement, the apparent PC, was 3-6 x 10-8 cm s-1. This value is in good agreement with those calculated from the rate constant of 36C1 efflux into both normal Krebs solution (steady-state) and Cl-free solution.3. Such a value for PC, predicts a large depolarization on removal of ClO, but only a minimal change was recorded. It also predicts that changes in membrane potential (Em) would affect a4 1; furthermore that removal of ClO would increase membrane resistance and thus the hyperpolarization observed on reactivation ofthe electrogenic Na pump. Neither of these was observed.4. The PC1/PK ratio obtained from changes in Em on rapid changes in ClO and K0 gives a value for PC1 which is an order of magnitude lower: 4 x 10-9 cm s-1, using Casteels' (1969b) value for PK. 5. These observations can be reconciled by a substantial proportion of the measured Cl movements being carrier-mediated. The presence of the stilbene derivative DIDS greatly slowed both the steady-state efflux and uptake of 36C1, as has previously been shown for the loss and reaccumulation of Cl ions on removal and replacement of ClO. PC, calculated in the presence of DIDS was about 5 x 10-9 cm s-1.The nominal absence of CO2 and HCO3, which slows the reaccumulation and loss of Cl, had no effect on the steady-state fluxes. This indicates that the carrier operates in the self-exchange mode in the steady-state.

Section: Comparison With Other Preparationssupporting

confidence: 65%

Section: Introductionmentioning

confidence: 82%

Towards an estimate of chloride permeability in the smooth muscle of guinea‐pig vas deferens.

Aickin¹,

Brading²

1983

“…The consequences of such a HC03-efflux were quantitatively analysed in squid giant axon by Boron & De Weer (1976 The internal Cl activity in normal polarized frog muscle, 2-5 mm (Bolton & Vaughan-Jones, 1977;) is considerably less than in other cells which exhibit SITS-sensitive recovery from acid loads. Thus, in invertebrates, Cli is 10-15 mm in snail neurone (Thomas, 1977), 30-40 mm in crayfish neurones (Moody, 1981) and barnacle muscle (Russell & Brodwick, 1979), and 100 mm in squid axon (Keynes, 1963). In mouse extensor digitorum longus or soleus muscle , Donaldson & Leader (1984) measured Cli of 5-3 mm, whereas Dulhunty (1978) computed a value of 12-5 mm.…”

Section: Discussionmentioning

confidence: 98%

Properties of the intracellular pH‐regulating systems of frog skeletal muscle.

Putnam¹,

Roos²,

Wilding³

1986

SUMMARY1. The properties of the systems that regulate intracellular pH (pHj) in frog muscle (Rana pipiens) were studied in semitendinosus fibres using pH-sensitive micro-electrodes. All experiments were done at 22 'C and at external pH (pHO) 7-35. 2. Normally polarized fibres acidified to pHi 3. The rate of recovery after an NH4Cl pulse increased linearly as pHi was reduced from 7-25 to 6-55. The dependence of this recovery upon external Na (at pHi 6 90) can be described by Michaelis-Menten kinetics; the apparent Michaelis constant (Ki) is 12+3 mM.4. Recovery of normally polarized fibres from acidification induced by 5 % CO2 is very slow (about 0-03 ApHi h-1). This recovery could be converted into an acidification of 0-06-0-07 ApHi h-1 either by removal of Na (as previously described) or by amiloride. We ascribe this acidification of the polarized fibres to HCO3-efflux.5. In fibres depolarized in 50 mM-K, at constant external Cl concentration, recovery from CO2 acidification was brisk (0-28 + 0.01 ApHi h-1, JH = 9.4 pmol cm-2 sol, n = 66

“…in red blood cells (Cabantchik & Rothstein, 1974), as well as an inhibitor of acid extrusion in barnacle muscle fibres (Boron, 1977). Furthermore, DIDS or SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid) are able to inhibit Cl-efflux in barnacle muscle fibres (Ashley, Ellory, Lea & Ramos, 1978;Russell & Brodwick, 1979;Bittar, Schultz & Tesar, 1980). The results of experiments show that the response of the ouabain-insensitive Na+ efflux to external application of 10-5 M-PD is drastically reduced when 10-4 M-DIDS is applied beforehand (337 + 37 %, n = 7 vs. 829 + 90 % in controls, n = 16, P < 0 01).…”

Section: Lack Of Effect Of Amiloridementioning

confidence: 99%

A study of the ouabain‐insensitive sodium efflux in barnacle muscle fibres using phorbol dibutyrate as a probe.

Bittar

Nwoga

1990

SUMMARY1. The resting ouabain-insensitive Na+ efflux in muscle fibres isolated from the barnacle, Balanus nubilus, is stimulated by external or internal application of phorbol 12,13-dibutyrate (PD). The response occurs fairly promptly and may not decay at all, or more commonly, decay rather slowly. The magnitude of the response to external or internal application of PD is dose-dependent, the minimum effective concentration being about 10-8 M.2. The response to PD fails to occur in the nominal absence of external Ca2+. Sudden removal of external Ca subsequent to peak stimulation by PD leads to almost complete reversal of the response. The response to PD of fibres suspended in Li+-ASW (artificial sea water) is similar in magnitude to that of fibres suspended in Na+-ASW. However, it differs in that it is of a sustained nature.3. Calcium channel blockers, e.g. verapamil, completely prevent the response to PD from occurring. Both Cd2+ and Co2+ are less effective than verapamil.4. Pre-but not post-injection of EGTA reduces the response to PD. Pre-or postinjection of Mg2+ reduces the response considerably.5. Fibres pre-injected with GTP show a reduced response to PD. Fibres preinjected with PD show a reduced response to GTP. Pre-injection of protein kinase inhibitor is without effect on the response to PD.6. Furosemide, piretanide and bumetanide are without effect on the response to PD. 7. DIDS (4,4'-diisothiocyanostilbene-2,2-disulphonic acid) is a potent inhibitor of the response to PD but not amiloride. Pyridoxal 5-phosphate and benzolamide are also powerful inhibitors. Pyridoxal 5-phosphate in combination with benzolamide fails to completely abolish or reverse the response to PD.8. Luminescence from aequorin is promptly increased by PD in a dose-dependent manner, the minimal effective concentration being in the nanomolar range. The signal is monophasic or multiphasic in shape, and is often less than 5 min in duration. Not infrequently, however, the aequorin response fails to completely decay and the new level of resting glow remains above the original baseline level.9. Collectively, these observations accord with a tentative general hypothesis stating that the stimulatory response of the ouabain-insensitive Na+ efflux to PD is triggered by two mechanisms. One involves a rise in myoplasmic free [Ca2+] resulting MS 7690 E2 E. BITTAR AND J. NWOGA from the entry of external Ca2+ via opened Ca2+ channels which is followed by the operation of the Na+{-Ca2+ exchanger in the reverse mode. The other involves stimulation of the Na+/HCO3--Cl-/H+ exchanger, presumably as the result of phosphorylation and/or an internal acidosis brought about by a sufficient rise in myoplasmic free [Ca2+].