Presence of two Ca2+ influx components in internal Ca2+-pool-depleted rat parotid acinar cells |
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Authors: | Jyoti V Chauthaiwale Takayuki Sakai Samuel E Taylor Indu S Ambudkar |
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Institution: | (1) Secretory Physiology Section, CIPCB, NIDR, NIH Bethesda MD 20892, USA., US;(2) Building 10 Room 1N-113, National Institutes of Health, Bethesda MD 20892, USA, US;(3) Department of Oral and Maxillafacial Surgery, Baylor Dental college, Dallas, TX, USA , US |
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Abstract: | The molecular mechanism(s) involved in mediating Ca2+ entry into rat parotid acinar and other non-excitable cells is not known. In this study we have examined the kinetics of
Ca2+ entry in fura-2-loaded parotid acinar cells, which were treated with thapsigargin to deplete internal Ca2+ pools (Ca2+-pool-depleted cells). The rate of Ca2+ entry was determined by measuring the initial increase in free cytosolic Ca2+] (Ca2+]i) in Ca2+-pool-depleted, and control (untreated), cells upon addition of various Ca2+] to the medium. In untreated cells, a low-affinity component was detected with K
Ca = 3.4 ± 0.7 mM (where K
Ca denotes affinity for Ca2+) and V
max = 9.8 ± 0.4 nM Ca2+]i /s. In thapsigargin-treated cells, two Ca2+ influx components were detected with K
Ca values of 152 ± 79 μM (V
max = 5.1 ± 1.9 nM Ca2+]i/s) and 2.4 ± 0.9 mM (V
max = 37.6 ± 13.6 nM Ca2+]i/s), respectively. We have also examined the effect of Ca2+ and depolarization on these two putative Ca2+ influx components. When cells were treated with thapsigargin in a Ca2+-free medium, Ca2+ influx was higher than into cells treated in a Ca2+-containing medium and, while there was a 46% increase in the V
max of the low-affinity component (no change in K
Ca), the high-affinity component was not clearly detected. In depolarized Ca2+-pool-depleted cells (with 50 mM KCl in the medium) the high-affinity component was considerably decreased while there was
an apparent increase in the K
Ca of the low-affinity component, without any change in the V
max. These results demonstrate that Ca2+ influx into parotid acinar cells (1) is increased (four- to five-fold) upon internal Ca2+ pool depletion, and (2) is mediated via at least two components, with low and high affinities for Ca2+.
Received: 30 October 1995/Received after revisionand accepted: 13 December 1995 |
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Keywords: | Ca2+ entry Kinetics Thapsigargin Parotid cells Fura-2 |
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