Some further observations on the stimulation by high external potassium of the sodium efflux in barnacle muscle fibers

Concerning stimulation by injected fluoroaluminate of the sodium efflux in barnacle muscle fibers

Single barnacle muscle fibers from Balanus nubilus were used primarily to examine the validity of two ideas: first, that the injection of KF stimulates the ouabain-insensitive Na+ efflux, and that this action is potentiated by adding AlCl3 (Al) in a low concentration to the solution of KF prior to injection. And second, that the injection of a KF-AlCl3 solution into ouabain-poisoned, K(+/-)-depolarized fibers elicits a stimulatory response resembling that obtained by injecting GTP. The results of this study are as follows: injection of 0.5 M KF into unpoisoned fibers causes a sustained rise in the resting Na+ efflux. However, injection of a 0.5 M KF, 10(-3) M AlCl3 solution leads to a reduced rather than an augmented response. Whereas injection of 0.5 M KF into ouabain-poisoned fibers elicits a marked stimulatory response, the injection of 0.5 M KF, 10(-3) M AlCl3 reduces the remaining Na+ efflux. Injection of KF-AlCl3 in equimolar concentrations, e.g., 0.25 M, elicits a response that is significantly larger than that obtained by injecting 0.25 M KF. A dose-response curve indicates that a 0.2 M solution of fluoroaluminate probably represents an optimal concentration. Injection of 0.3 M KF following peak stimulation by injecting 0.3 M AlCl3 completely reverses this response to Al. In sharp contrast, injection of a 0.3 M KF, 0.3 M AlCl3 mixture following peak stimulation by injecting 0.3 M AlCl3 is ineffective. Injection of KF into ouabain-poisoned, K+ depolarized fibers does not always cause sustained stimulation of the remaining Na+ efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

An investigation of the sensitivity of the ouabain-insensitive sodium efflux in single barnacle muscle fibers to pentachlorophenol

The aim of the present work was to explore the possibility that pentachlorophenol (PCP) influences the behavior of the resting Na efflux in single muscle fibers from the barnacle, Balanus nubilus. It is shown here that PCP causes a transitory rise in the Na efflux in both unpoisoned and ouabain-poisoned fibers and that the response is dose-dependent, the minimal effective concentration in ouabain treated fibers being less than 10(-6) M. The efficacy of PCP is significantly greater than that of 2,3,4-trichlorophenol. 2,3-Dichlorophenol is ineffective. This is also the case with phenol. The magnitude of the response to PCP is a function of external pH. Lowering pHe increases the response. The response has an absolute requirement for external Ca2+ and is a sigmoidal function of external Ca2+ concentration. Since treatment of these fibers with PCP in high concentration leads to prompt contraction, experiments were designed to determine whether the observed rise in ouabain-insensitive Na efflux is due to a fall in myoplasmic pCa and whether trigger Ca2+ originates from the bathing medium. The results obtained show that prior injection of ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) or 1,2-bis(2-aminophenoxyethane-N,N,N',N'-tetraacetic acid (BAPTA) leads to a drastic reduction in the response to PCP. They also show that prior external application of verapamil or devapamil stops the response to PCP from occurring. Both Cd2+ and Co2+ are also effective but only temporarily. Last, the effects of ryanodine and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) were tested, since the former is known to block the sarcoplasmic reticulum Ca2+ release channel, and the latter to impair the action of agents known to release Ca2+ from internal depots. Both ryanodine and TMB-8 are found to reduce the response to PCP. Taken together, these observations support the hypothesis that PCP stimulates the ouabain-insensitive Na efflux by increasing the internal free Ca2+ and that the increase in internal Ca2+ is due to the entry of trigger Ca2+ from the outside via Ca2+ channels, as well as release of Ca2+ by the sarcoplasmic reticulum via its channel. They also indicate that the efficacy of PCP depends on the 5 Cl atoms present in its aromatic ring and pHe.

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

1. 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 post-injection of Mg2+ reduces the response considerably. 5. Fibres pre-injected with GTP show a reduced response to PD. Fibres pre-injected 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 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensitivity of the sodium efflux in single barnacle muscle fibers to the microinjection of aluminum

A study has been made of the behavior of the Na efflux in single muscle fibers from the barnacle, Balanus nubilus, toward the microinjection of AlCl3. The effect of microinjecting AlCl3 is either biphasic with inhibition following transitory stimulation, or monophasic with inhibition occurring promptly and taking about 1 hr to reach a maximum. The magnitude of the inhibition is dose dependent and the minimally effective concentration is 10 mM. This is diluted by the myoplasm by a factor of roughly 100. Fibers injected with 1 M AlCl3 are found to be insensitive to 10(-4) M ouabain, whereas fibers injected with 0.5 M AlCl3 show a further fall in Na efflux, which is smaller than that seen in control fibers. The response of the ouabain-insensitive Na efflux to the injection of 0.5 M AlCl3 is biphasic: stimulation is followed by inhibition. The stimulatory phase is largely dependent on the presence of external Ca2+ and is reversed by the sudden omission of Ca2+ from the bathing medium. Fibers also injected with 0.5 M AlCl3 show a marked reduction in the response of the Na efflux to high external K. Injection of ATPMg before or after the injection of AlCl3 fails in most instances to abolish or reverse the inhibitory effect. By contrast, fibers preinjected with deferoxamine show little or no effect following the injection of AlCl3. However, external application of deferoxamine is ineffective.

Further observations on the behaviour of ouabain-insensitive sodium efflux towards proctolin in barnacle muscle fibres

1. A further study has been made of the stimulatory action of proctolin on the ouabain-insensitive Na+ efflux in single muscle fibres from the barnacle, Balanus nubilus. 2. (i) Strontium (Sr2+) behaves as a substitute for external Ca2+. In this case, however, the response to proctolin fails to decay. (ii) Injection of Sr2+ stimulates the ouabain-insensitive Na+ efflux. This effect is mimicked by injecting Ca2+. 3. Depolarization of the fibre membrane with 30 and 100 mM-external K+ augments the response to proctolin. 4. Pre-injection of GTP or Gpp(NH)p (sodium 5-guanylylimidodiphosphate) prevents the response to proctolin from completely decaying. 5. Pre-injection of guanine nucleotides in conjunction with membrane depolarization stops the response to proctolin from decaying. 6. Measurements of Em before and during treatment with proctolin indicate a prompt but small and reversible fall in the membrane potential. 7. (i) The aequorin response of fibres pre-treated with ouabain to proctolin is monophasic or multiphasic, and concentration dependent, the minimal effective concentration being in the nanomolar range. (ii) The duration of these signals is usually less than 5 min; this is about half the time it takes for the stimulated Na+ efflux to reach a maximum. (iii) The aequorin response to proctolin occurs quite often in fibres suspended in nominally Ca2(+)-free artificial sea water. (iv) Sudden graded elevations in external K+ following complete decay of the aequorin response to proctolin are rapidly followed by stepwise transitory increments in light emission. (v) The aequorin response to 100 mM-external K+ is frequently a triplet. 8. (i) Together, these results are in line with the view that the action of proctolin on the ouabain-insensitive Na+ efflux is the result of a temporary fall in internal pCa and that its point of action is the Ca2+ channel, where a putative G protein in the presence of GTP or Gpp(NH)p is able to maintain constancy of the hormonal effect. (ii). They strengthen the argument that the barnacle muscle fibre as a preparation is especially suitable for studies of this kind.

Concerning stimulation by high external potassium and calcium injection of the ouabain-insensitive sodium efflux in barnacle muscle fibers

The behavior of the ouabain-insensitive Na efflux in barnacle muscle fibers toward external high K and injection of Ca2+ has been further investigated. Raising Ke to 100 mM after the injection of 0.25 M or 0.1 M GTPNa2 results in a biphasic stimulatory response: the initial response is prompt in onset and small but transitory, whereas the delayed response is large and sustained. This second stimulatory phase is reduced markedly by injecting EGTA but not by PKI. Raising Ke to 100 mM in the presence of the 2 xanthine derivatives, viz. PMX and IAX, leads to a sustained stimulatory response of the ouabain-insensitive Na efflux which is halved by injecting PKI but unaffected by injecting EGTA. Injection of 0.1 M or 0.5 M CaCl2 in the presence of PMX and IAX leads to a sustained stimulatory response, which is almost completely abolished by injecting PKI but unaffected by injecting EGTA. These results confirm the earlier finding that the response of the ouabain-insensitive Na efflux to high Ke in fibers preinjected with GTPNa2 is biphasic and that the delayed second stimulatory phase is sustained rather than transitory. The ability of injected EGTA to only partially reverse the delayed response suggests that a fall in myoplasmic pCa is not the sole factor governing the kinetic picture. The experiments with PMX and IAX strongly suggest that cAMP is involved in the termination of the Ca2+ message.

Evidence for the presence of protein kinase C in barnacle muscle fibers

1. The efflux of 22Na from single barnacle muscle fibers poisoned with ouabain (strophanthin G) is found to be very sensitive to the tumor-promoting agent, phorbol dibutyrate (PDBu). 2. Injection or external application of PDBu leads to stimulation of the ouabain-insensitive component of the Na efflux. This response is dose-dependent, the minimal effective concentration being about 10(-8)M. 3. The observed stimulatory response is completely dependent on the presence of external Ca2+. 4. Biochemical studies including immunoblot analysis reveal the presence in barnacle muscle of a protein kinase C with a mol. wt of 80,000, the activity of which is dependent on phosphatidylserine and Ca2+. 5. Taken together, these results support the view that barnacle muscle fibers possess protein kinase C. They also raise the possibility that protein kinase C plays a role in modulating the ouabain-insensitive component of the Na efflux.

The modulatory action of 5-hydroxytryptamine on sodium efflux: the barnacle muscle fibre as a model system

A study has been made of the action of 5-hydroxytryptamine (5-HT) on the radio-sodium efflux from single barnacle muscle fibres. (i) Stimulation of the Na efflux by external application of 5-HT is seen in both unpoisoned and ouabain-poisoned fibres. (ii) Concentrations of 5-HT as low as 10(-9)M are effective. (iii) Characteristically, the response to 5-HT is prompt in onset, reaches a peak within 20 min and then decays rather rapidly. Fibres from certain barnacle specimens are sometimes unresponsive to 5-HT. Such fibres, however, can be rendered responsive by preinjecting into them the non-hydrolysable GTP analogue, Gpp(NH)p. The response of the ouabain-insensitive Na efflux to 5-HT depends on external Ca2+ and, to a certain extent, on external Na+. (i) The response to 5-HT is unaffected by prior external application of Ca2+ antagonists, viz. verapamil, Cd2+ and WB-4101. (ii) The calmodulin antagonist, trifluoperazine (10(-5)M), completely abolishes the response to 5-HT, even in fibres preinjected with Gpp(NH)p. (iii) Diphenylhydantoin is less effective than trifluoperazine (TFP). Whereas the receptor antagonist methysergide is ineffective, cyproheptadine is very effective. (i) Prior application of the phosphodiesterase inhibitor 1-propyl-3-methyl-7-(5-hydroxyhexyl)-xanthine (PMX) or the inhibitor 1-isoamyl-3-isobutyl-xanthine (IAX) augments the size of the response to 5-HT, but fails to stop the response from decaying. (ii) Augmentation of the response to 5-HT by IAX is seen despite the presence of 10(-5) M-TFP. Prior injection of Mg2+ or protein kinase inhibitor (PKI) leads to abolition or reduction of the response to 5-HT. These results demonstrate that barnacle fibres are a useful preparation for investigation the natriferic action of 5-HT. They also support the view that the response to 5-HT involves a receptor-adenylate cyclase complex and is the result of activation by newly formed cAMP of cAMP-dependent protein kinase.

Stimulation by proctolin of the ouabain-insensitive sodium efflux in single barnacle muscle fibers

A study has been made of the action of the neuropeptide proctolin on the radiosodium efflux from single barnacle muscle fibers. Proctolin (10(-8) M) when applied externally causes stimulation of the Na efflux in unpoisoned and ouabain-poisoned fibers. The response is prompt in onset, reaches a peak in 15 min and decays slowly. The response of the ouabain-insensitive Na efflux to external proctolin is dose-dependent, the concentration threshold being less than 10(-10) M. The response to proctolin is dependent on external Ca2+ but not on Na+. (i) The response to proctolin is abolished by high external Mg2+, as well as by verapamil, Co2+, Cd2+ and WB-4101. (ii) The response is also abolished by preinjecting 0.5 M MgCl2 or 0.1 M EGTA. The calmodulin antagonists trifluoperazine and imipramine are without effect on the response to proctolin. (i) Adenylate cyclase agonists, e.g. forskolin, fail to augment the response to proctolin. (ii) Prior injection of the phosphodiesterase inhibitors 1-propyl-3-methyl-7-(5-hydroxyhexyl)-xanthine (PMX) or 1-isoamyl-3-isobutylxanthine (IAX) fails to augment the response to proctolin. (iii) Prior injection of protein kinase inhibitor is ineffective. The response to proctolin is significantly reduced in the presence of tyramine. Taken together, these results support the view that proctolin stimulates the ouabain-insensitive Na efflux by activating Ca2+ channels and that the cAMP-protein kinase system is not involved in this response.

Some observations on the behaviour of the sodium efflux in barnacle muscle fibres towards lithium ions

The behaviour of the Na efflux towards Li+ was studied using single barnacle muscle fibres as a preparation. It is found that the Na efflux into Li+-ASW (artificial seawater) is reduced and that this effect is not fully reversed by returning back to Na+-ASW. Preinjection of 100 mM-EGTA reduces the magnitude of the fall of the Na efflux into Li+-ASW. The remaining Na efflux into Li+-ASW is further reduced by external application of 10(-4) M-ouabain. The remaining Na efflux in ouabain-poisoned fibres is reduced by replacing Nae by Li+. However, some fibres show a rise rather than a fall. Fibres loaded with NaCl (by injection) show a prompt and sustained stimulation of the Na efflux when Nae is replaced by Li+. A similar but less pronounced response is often seen with ouabain-poisoned fibres. Injection of LiCl (e.g. a 2 M-solution), causes a 20% fall in Na efflux. Subsequent replacement of Nae by Li+ fails to bring about a fall in the remaining efflux. It is concluded that the Na efflux in these fibres consists of a Na-Na exchange diffusion component which is not mediated by the Na-K pump and that its operation is interrupted by injecting Li+. The relative size of this component is about one-fifth and not one-half of the Na efflux.

Some aspects of sodium efflux from single barnacle muscle fibres

This mini-review attempts to summarize information about the efflux of 22Na from single barnacle muscle fibres, based on the use of the microinjection technique. The view is put forward that the Na efflux consists of three components: an ouabain-sensitive component, an ouabain-insensitive component (representing secondary active transport), and an Na-Na exchange diffusion component. Evidence is brought forward which supports the view that the ouabain-insensitive Na efflux is divisible operationally into 3 phases: (i) the cyclic nucleotide-sensitive phase, (ii) the Cai-sensitive phase, and (iii) the pHe-sensitive phase. It is shown how the barnacle muscle fibre preparation has yielded information about the validity of the cAMP-protein kinase hypothesis and how it can be used to shed some light on the post-translational mechanism of aldosterone action.