The Thermodynamic Activity of Calcium Ion in Sodium Chloride-Calcium Chloride Electrolytes

Butler, James N.

doi:10.1016/s0006-3495(68)86564-6

Cited by 90 publications

(64 citation statements)

References 11 publications

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“…The first is that the Na, K and Ca are fully ionized on both sides of the cell membrane. Butler (1968) has shown that this is not the case in physiological media and there may be some differences between the measurements of Na intracellular content and the activity of Na in the sarcoplasm. The second assumes that there are no assymetries in the Na-Ca exchange, whereas Glitsch et al (1970) have obtained evidence of affinity differences between the inside and outside of guinea-pig atrial muscle cells which would favour Ca efflux and Na influx.…”

Section: Discussionmentioning

confidence: 99%

The interaction of sodium and calcium ions at the cell membrane and the control of contractile strength in frog atrial muscle.

Chapman¹,

Tunstall²

1980

The Journal of Physiology

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4. The only scheme to fit all the experimental data satisfactorily is one which assumes an exchange of one Ca ion for three Na ions across the membrane. This scheme requires that the contractile system has an apparent binding constant for Ca2+, similar to that found with skinned cardiac muscle cells or isolated cardiac myofibrils. In intact muscle, when the [Na]1 is close to that measured experimentally, the model predicts that tension should vary with the [Ca]

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Section: Discussionmentioning

confidence: 99%

The interaction of sodium and calcium ions at the cell membrane and the control of contractile strength in frog atrial muscle.

Chapman¹,

Tunstall²

1980

The Journal of Physiology

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“…To determine the relative permeability to divalent cations, the GHK equation was modified to include divalent cations and activity coefficients (see Fieber & Adams, 1991). Activity coefficients of the salts were obtained from Butler (1968) and Robinson & Stokes (1965).…”

Section: Discussionmentioning

confidence: 99%

Ionic selectivity of native ATP‐activated (P2X) receptor channels in dissociated neurones from rat parasympathetic ganglia

Adams

2001

The Journal of Physiology

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5. Acidification to pH 6.2 increased the ATP-induced current amplitude twofold, whereas alkalization to 8.2 and 9.2 markedly reduced current amplitude. Cell dialysis with either anti-P2X 2 and/or anti-P2X 4 but not anti-P2X 1 antibodies attenuated the ATP-evoked current amplitude. Taken together, these data are consistent with homomeric and/or heteromeric P2X 2 and P2X 4 receptor subtypes expressed in rat submandibular neurones.6. The permeability ratios for the series of monovalent organic cations, with the exception of unsaturated cations, were approximately related to the ionic size. The relative permeabilities of the monovalent inoganic and organic cations tested are similar to those reported previously for cloned rat P2X 2 receptors expressed in mammalian cells.

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“…The calculated single ion activity coefficient of Ca 2ϩ also varies slightly with concentration of added CaCl 2 . Using the mean activity coefficient values for CaCl 2 reported in Butler (28) and the Guggenheim assumption of the Debye-Huckel theory, a ϳ20% change in single ion activity coefficient of Ca 2ϩ was calculated for solutions of ionic strength between 0.1 and 0.2 M. The EC 50 for Ca 2ϩ stimulation of CaR-dependent cytosolic calcium responses was 1 mM in our standard HEPESbuffered solution when expressed as Ca 2ϩ activity and onethird of the shift in the EC 50 , which is dependent on ionic strength, can be accounted for by these changes in Ca 2ϩ activity (28). Our data and these estimations of Ca 2ϩ activity suggest that the effects of ionic strength on CaR activation may be due to changes in the Ca 2ϩ activity at a given ionized or added Ca 2ϩ concentration as well as changes in electrostatic interactions within the receptor itself.…”

Section: Ionic Strength and The Relative Degree Of Activation For Carmentioning

confidence: 99%

Sodium and Ionic Strength Sensing by the Calcium Receptor

Quinn

Kifor

Trivedi

et al. 1998

Journal of Biological Chemistry

130

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within its physiological range of ϳ1.5 mM (1, 2). Initially cloned from bovine parathyroid cells, the CaR is highly expressed in the tissues involved in regulating [Ca 2ϩ ] o including the parathyroid (PT), calcitonin-secreting cells of the thyroid (C cells), and several regions of the kidney (1, 3, 4). Interestingly, the CaR is also distributed in a number of other tissues which do not have well established roles in the control of [Ca 2ϩ ] o . These include several regions of the brain (e.g. the subfornical organ and hypothalamus), the pituitary, collecting duct of the kidney, lung, and the intestines (1,(5)(6)(7)(8). In many of these tissues the physiological role of the CaR is not understood. One possibility is that the CaR senses endogenous ligands other than [Ca 2ϩ ] o , thus allowing the CaR to function in a number of specialized capacities in different CaR-expressing tissues.The CaR is activated by both polyvalent cations and polycationic molecules that interact with the extracellular domain of the receptor (1, 9). This might take place through the screening of charged side chains of acidic or basic amino acids, rather than the more classical binding through hydrogen bonding and salt bridges. If its endogenous agonists act by screening charges on the CaR, then activation of the receptor by these ligands should be modulated by conditions such as changes in ionic strength (10). With the addition of salts, the ionic strength will increase and the ability of the polycationic ligand to activate the CaR should be diminished. Likewise, the removal of salts and the resultant decrease in ionic strength should have the opposite effect. These effects of ionic strength can be explained by changes in the Debye length of the electrical field surrounding the charged agonist. The Debye length is inversely proportional to the square root of the ionic strength of the extracellular solution. For example, addition of NaCl would increase the ionic strength of the solution and should increase the concentration of [Ca 2ϩ ] o required for half-maximal activation of the CaR. Interestingly, the N-methyl-D-aspartate receptor shares some regions of homology with the CaR, and both receptors can be modulated by divalent cations, spermine and polycationic molecules such as neomycin (11)(12)(13)(14). Furthermore, modulation of the N-methyl-D-aspartate receptor by spermine and pH are susceptible to ionic strength, suggesting that they may also act through charge screening (10).Ionic strength can have substantial effects on a number of different cell types, particularly those involved in the regulation of fluid volume, osmolality and extracellular sodium. The subfornical organ and hypothalamus regulate the secretion of vasopressin by sensing the systemic levels of various hormones, including angiotensin II, and the level of NaCl (15-17). Early studies using injections of NaCl into these regions of the brain suggested that there existed a sodium sensor, since NaCl injections were much more effective in the control of vasopressin an...

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The Thermodynamic Activity of Calcium Ion in Sodium Chloride-Calcium Chloride Electrolytes

Cited by 90 publications

References 11 publications

The interaction of sodium and calcium ions at the cell membrane and the control of contractile strength in frog atrial muscle.

The interaction of sodium and calcium ions at the cell membrane and the control of contractile strength in frog atrial muscle.

Ionic selectivity of native ATP‐activated (P2X) receptor channels in dissociated neurones from rat parasympathetic ganglia

Sodium and Ionic Strength Sensing by the Calcium Receptor

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