scholarly journals Effects of extracellular ATP on ion transport systems and [Ca2+]i in rat parotid acinar cells. Comparison with the muscarinic agonist carbachol.

1990 ◽  
Vol 95 (2) ◽  
pp. 319-346 ◽  
Author(s):  
S P Soltoff ◽  
M K McMillian ◽  
E J Cragoe ◽  
L C Cantley ◽  
B R Talamo
Keyword(s):  
Relative Proportion ◽  
Acinar Cells ◽  
Initial Response ◽  
Extracellular Atp ◽  
Cation Channel ◽  
Transport Systems ◽  
K Channel ◽  
Muscarinic Agonist ◽  
Parotid Acinar Cells ◽  
Rat Parotid

The effects of extracellular ATP on ion fluxes and the intracellular free Ca2+ concentration ([Ca2+]i) were examined using a suspension of rat parotid acinar cells and were contrasted with the effects of the muscarinic agonist carbachol. Although ATP and carbachol both rapidly increased [Ca2+]i about threefold above the resting level (200-250 nM), the effect of ATP was due primarily to an influx of Ca2+ across the plasma membrane, while the initial response to carbachol was due to a release of Ca2+ from intracellular stores. Within 10 s, ATP (1 mM) and carbachol (20 microM) reduced the cellular Cl- content by 39-50% and cell volume by 15-25%. Both stimuli reduced the cytosolic K+ content by 57-65%, but there were marked differences in the rate and pattern of net K+ movement as well as the effects of K+ channel inhibitors on the effluxes initiated by the two stimuli. The maximum rate of the ATP-stimulated K+ efflux (approximately 2,200 nmol K+/mg protein per min) was about two-thirds that of the carbachol-initiated efflux rate, and was reduced by approximately 30% (vs. 60% for the carbachol-stimulated K+ efflux) by TEA (tetraethylammonium), an inhibitor of the large conductance (BK) K+ channel. Charybdotoxin, another K+ channel blocker, was markedly more effective than TEA on the effects of both agonists, and reduced the rate of K+ efflux initiated by both ATP and carbachol by approximately 80%. The removal of extracellular Ca2+ reduced the ATP- and the carbachol-stimulated rates of K+ efflux by 55 and 17%, respectively. The rate of K+ efflux initiated by either agonist was reduced by 78-95% in cells that were loaded with BAPTA to slow the elevation of [Ca2+]i. These results indicated that ATP and carbachol stimulated the efflux of K+ through multiple types of K(+)-permeable channels, and demonstrated that the relative proportion of efflux through the different pathways was different for the two stimuli. ATP and carbachol also stimulated the rapid entry of Na+ into the parotid cell, and elevated the intracellular Na+ content to 4.4 and 2.6 times the normal level, respectively. The rate of Na+ entry through Na(+)-K(+)-2Cl- cotransport and Na(+)-H+ exchange was similar whether stimulated by ATP, carbachol, or ionomycin, and uptake through these two carrier-mediated transporters accounted for 50% of the ATP-promoted Na+ influx. The remainder may be due to a nonselective cation channel and an ATP-gated cation channel that is also permeable to Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of secretagogue-induced HCO3- and Cl- loss from rat parotid acini

1991 ◽  
Vol 261 (1) ◽  
pp. G111-G118 ◽  
Author(s):  
S. I. Lee ◽  
R. J. Turner
Keyword(s):  
Acinar Cells ◽  
Time Dependent ◽  
K Channel ◽  
Channel Blockers ◽  
Muscarinic Agonist ◽  
Transport Pathways ◽  
Parotid Acinar Cells ◽  
Muscarinic Response ◽  
Muscarinic Stimulation ◽  
Rat Parotid

The Cl(-)- and HCO3(-)-dependent components of muscarinic agonist (carbachol)-induced K+ loss from a rat parotid mince were studied using 86Rb+ as a K+ marker. Both components of 86Rb+ loss were blunted by K+ and Cl- channel blockers and by removal of extracellular Ca2+, consistent with the hypothesis that 86Rb+ loss occurs via a Ca(2+)-activated K+ channel and that this cation loss serves to electrically balance a concomitant loss of the corresponding anion via one or more conductive pathways (channels). Two tissue "pools" of 86Rb+ were observed, a carbachol-sensitive pool and a carbachol-insensitive pool (approximately 70 and approximately 30% of the total 86Rb+ content, respectively). There was no evidence for a time-dependent desensitization of the muscarinic response of the carbachol-sensitive pool. Cl(-)-dependent 86Rb+ loss was not affected by HCO3- addition, suggesting that both Cl- and HCO3- secretion are accompanied by 86Rb+ loss from the same pool and thus occur from the same cells. HCO3(-)-dependent 86Rb+ loss was not enhanced by lowering the extracellular Na+ concentration, indicating that the HCO3- exit pathway is not a Na(+)-HCO3- symport. The data are consistent with the postulate that Cl- and HCO3- are secreted by rat parotid acinar cells via the same or very similar conductive transport pathways in response to muscarinic stimulation.

ATP activates a cation-permeable pathway in rat parotid acinar cells

1992 ◽  
Vol 262 (4) ◽  
pp. C934-C940 ◽  
Author(s):  
S. P. Soltoff ◽  
M. K. McMillian ◽  
B. R. Talamo
Keyword(s):  
Membrane Potential ◽  
Uptake Rate ◽  
Purinergic Receptor ◽  
Acinar Cells ◽  
Muscarinic Agonist ◽  
Tetraacetic Acid ◽  
Nucleotide Analogues ◽  
Parotid Acinar Cells ◽  
Biphasic Effect ◽  
Rat Parotid

Effects of several purinergic receptor agonists were examined on rat parotid acinar cells. Extracellular ATP stimulated 45Ca2+ uptake into isolated rat parotid acinar cells in a concentration-dependent fashion (EC50 approximately 125 microM ATP) at a maximum rate of approximately 6 nmol.mg protein-1.min-1. In the absence of extracellular Na+, ATP increased the uptake rate by greater than 100%. Increasing concentrations of extracellular Na+ reduced the ATP-stimulated rate of 45Ca2+ entry in a graded fashion (IC50 16.6 mM), suggesting that Ca2+ and Na+ compete for entry. Uptake rate was not reduced when intracellular Ca2+ was buffered with 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid, indicating that the effects of ATP were not initiated by an elevation in intracellular free Ca2+ concentration. 3-O-(4'-benzoyl)benzoyl-ATP was much more potent (EC50 approximately 4 microM) and stimulated Ca2+ influx at a greater rate (approximately 12 nmol.mg protein-1.min-1) than ATP. Other nucleotide analogues, including adenosine 5'-O-(3-thiotriphosphate), 2-methylthio-ATP, and 5'-adenylylimidodiphosphate, were much less effective than ATP. ATP produced a biphasic effect on membrane potential: an initial hyperpolarization was followed by a rapid depolarization. The depolarization was greatly reduced in the absence of extracellular Na+, but not in the absence of extracellular Ca2+, indicating that the majority of the depolarizing current was due to Na+ entry. Effects of ATP on the membrane potential were distinguishable from those of the Ca2+ ionophore ionomycin and the muscarinic agonist carbachol. Depolarization of the cells by gramicidin or K+ did not produce an increase in 45Ca2+ uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Effects of muscarinic, alpha-adrenergic, and substance P agonists and ionomycin on ion transport mechanisms in the rat parotid acinar cell. The dependence of ion transport on intracellular calcium.

1989 ◽  
Vol 93 (2) ◽  
pp. 285-319 ◽  
Author(s):  
S P Soltoff ◽  
M K McMillian ◽  
L C Cantley ◽  
E J Cragoe ◽  
B R Talamo
Keyword(s):  
Substance P ◽  
Ion Transport ◽  
Acinar Cell ◽  
Fluid Secretion ◽  
Ion Fluxes ◽  
Transport Systems ◽  
K Channel ◽  
Muscarinic Agonist ◽  
Parotid Acinar Cell ◽  
Rat Parotid

The relationship between receptor-mediated increases in the intracellular free calcium concentration [( Ca]i) and the stimulation of ion fluxes involved in fluid secretion was examined in the rat parotid acinar cell. Agonist-induced increases in [Ca]i caused the rapid net loss of up to 50-60% of the total content of intracellular chloride (Cli) and potassium (Ki), which is consistent with the activation of calcium-sensitive chloride and potassium channels. These ion movements were accompanied by a 25% reduction in the intracellular volume. The relative magnitudes of the losses of Ki and the net potassium fluxes promoted by carbachol (a muscarinic agonist), phenylephrine (an alpha-adrenergic agonist), and substance P were very similar to their characteristic effects on elevating [Ca]i. Carbachol stimulated the loss of Ki through multiple efflux pathways, including the large-conductance Ca-activated K channel. Carbachol and substance P increased the levels of intracellular sodium (Nai) to more than 2.5 times the normal level by stimulating the net uptake of sodium through multiple pathways; Na-K-2Cl cotransport accounted for greater than 50% of the influx, and approximately 20% was via Na-H exchange, which led to a net alkalinization of the cells. Ionomycin stimulated similar fluxes through these two pathways, but also promoted sodium influx through an additional pathway which was nearly equivalent in magnitude to the combined uptake through the other two pathways. The carbachol-induced increase in Nai and decrease in Ki stimulated the activity of the sodium pump, measured by the ouabain-sensitive rate of oxygen consumption, to nearly maximal levels. In the absence of extracellular calcium or in cells loaded with the calcium chelator BAPTA (bis[o-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid) the magnitudes of agonist- or ionomycin-stimulated ion fluxes were greatly reduced. The parotid cells displayed a marked desensitization to substance P; within 10 min the elevation of [Ca]i and alterations in Ki, Nai, and cell volume spontaneously returned to near baseline levels. In addition to quantitating the activation of various ion flux pathways in the rat parotid acinar cell, these results demonstrate that the activation of ion transport systems responsible for fluid secretion in this tissue is closely linked to the elevation of [Ca]i.

scholarly journals Two distinct cytosolic calcium responses to extracellular ATP in rat parotid acinar cells

1993 ◽  
Vol 108 (2) ◽  
pp. 453-461 ◽  
Author(s):  
Michael K. McMillian ◽  
Stephen P. Soltoff ◽  
Lewis C. Cantley ◽  
RuthAnn Rudel ◽  
Barbara R. Talamo
Keyword(s):  
Acinar Cells ◽  
Cytosolic Calcium ◽  
Extracellular Atp ◽  
Parotid Acinar Cells ◽  
Rat Parotid
Sign in / Sign up

Export Citation Format

Share Document