Effects of MeCh, thapsigargin, and La3+ on plasmalemmal and intracellular Ca2+ transport in lacrimal acinar cells

TY - JOUR

T1 - Effects of MeCh, thapsigargin, and La3+ on plasmalemmal and intracellular Ca2+ transport in lacrimal acinar cells

AU - Kwan, C Y

AU - Takemura, H

AU - Obie, J F

AU - Thastrup, Ole

AU - Putney, J W

PY - 1990

Y1 - 1990

N2 - The Ca2(+)-mobilizing actions of the muscarinic receptor agonist, methacholine (MeCh), and the microsomal Ca2+ pump inhibitor, thapsigargin, were investigated in lacrimal acinar cells. As previously shown for parotid cells (J. Biol. Chem. 264: 12266-12271, 1989), thapsigargin activates both internal Ca2+ release and Ca2+ entry from the extracellular space without increasing cellular inositol phosphates. The inorganic Ca2+ antagonist La3+ inhibited MeCh- or thapsigargin-activated Ca2+ entry. However, when added before MeCh or thapsigargin, La3+ inhibited the extrusion of Ca2+ at the plasma membrane. This phenomenon was exploited in protocols designed to investigate the pathways for filling agonist-sensitive Ca2+ stores in lacrimal cells. The results show that, in contrast to previous suggestions that external Ca2+ is required to replenish agonist-regulated Ca2+ stores, the inhibition of Ca2+ extrusion permits recycling of Ca2+ released by MeCh back into an MeCh- and thapsigargin-sensitive pool. Thus, although extracellular Ca2+ is the major source for refilling the intracellular Ca2+ stores under physiological conditions, the pathway by which this Ca2+ enters the pool need not be a direct one. These results are consistent with the recently revised capacitative model for the refilling of intracellular Ca2+ stores through Ca2+ influx subsequent to Ca2+ depletion, according to which refilling of intracellular Ca2+ stores occurs via a cytoplasmic route rather than a direct channel between intracellular Ca2+ stores and the extracellular space.

AB - The Ca2(+)-mobilizing actions of the muscarinic receptor agonist, methacholine (MeCh), and the microsomal Ca2+ pump inhibitor, thapsigargin, were investigated in lacrimal acinar cells. As previously shown for parotid cells (J. Biol. Chem. 264: 12266-12271, 1989), thapsigargin activates both internal Ca2+ release and Ca2+ entry from the extracellular space without increasing cellular inositol phosphates. The inorganic Ca2+ antagonist La3+ inhibited MeCh- or thapsigargin-activated Ca2+ entry. However, when added before MeCh or thapsigargin, La3+ inhibited the extrusion of Ca2+ at the plasma membrane. This phenomenon was exploited in protocols designed to investigate the pathways for filling agonist-sensitive Ca2+ stores in lacrimal cells. The results show that, in contrast to previous suggestions that external Ca2+ is required to replenish agonist-regulated Ca2+ stores, the inhibition of Ca2+ extrusion permits recycling of Ca2+ released by MeCh back into an MeCh- and thapsigargin-sensitive pool. Thus, although extracellular Ca2+ is the major source for refilling the intracellular Ca2+ stores under physiological conditions, the pathway by which this Ca2+ enters the pool need not be a direct one. These results are consistent with the recently revised capacitative model for the refilling of intracellular Ca2+ stores through Ca2+ influx subsequent to Ca2+ depletion, according to which refilling of intracellular Ca2+ stores occurs via a cytoplasmic route rather than a direct channel between intracellular Ca2+ stores and the extracellular space.

KW - Animals

KW - Benzofurans

KW - Biological Transport, Active

KW - Calcium

KW - Carcinogens

KW - Cell Membrane

KW - Fluorescent Dyes

KW - Fura-2

KW - Inositol Phosphates

KW - Kinetics

KW - Lacrimal Apparatus

KW - Lanthanum

KW - Methacholine Compounds

KW - Mice

KW - Models, Biological

KW - Rats

KW - Receptors, Muscarinic

KW - Signal Transduction

KW - Terpenes

KW - Thapsigargin

M3 - Journal article

C2 - 2360617

SN - 0002-9513

VL - 258

SP - C1006-15

JO - American Journal of Physiology

JF - American Journal of Physiology

IS - 6 Pt 1

ER -