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Serum‐stimulated changes in calcium transport and distribution in mouse 3T3 cells and their modification by dibutyryl cyclic AMP
Author(s) -
Tupper Joseph T.,
Rosso Mario Del,
Hazelton Bonnie,
Zorgniotti Flavia
Publication year - 1978
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1040950110
Subject(s) - egta , stimulation , cytoplasm , calcium , chemistry , 3t3 cells , biophysics , endocrinology , medicine , biochemistry , biology , transfection , organic chemistry , gene
Serum stimulation of quiescent 3T3 cells returns the cells to a proliferative state. Changes in Ca content, transport and distribution during the transition through G 1 and S phase have been investigated following serum stimulation of these cells. 45 Ca exchange data indicate at least two kinetically defined cellular compartments for Ca; a rapidly exchanging component presumably representing surface Ca which is removable by EGTA and a slowly exchanging component presumably representing cytoplasmically located Ca. Previous studies (Tupper and Zorgniotti, 1977) indicate that the approach to quiescence in the 3T3 cells is characterized by a large increase in the surface Ca component. The present data demonstrate that this component is rapidly lost following serum stimulation. Furthermore, the serum induces an 8‐fold increase in Ca influx into the cytoplasmic compartment and a reduction in the unidirectional efflux rate coefficient for Ca. The increased Ca uptake peaks at approximately six hours (mid G1) and is accompanied by a parallel increase in cellular Ca. Prior to entrance of the cells into S phase (10—12 hours), Ca uptake declines. This is followed by a slower decline in cytoplasmic Ca levels. Simultaneous addition of fresh serum plus 0.5 mM dibutyryl cAMP inhibits the entrance of the cells into S phase. Under these conditions the loss of surface Ca is not blocked. However, the presence of 0.5 mM dibutyryl cAMP inhibits the increase in Ca uptake and, in turn, diminishes the increase in cellular Ca following serum stimulation. In contrast, a low level of dibutyryl cAMP (0.1 mM) enhances progression through G1 phase but also reduces both Ca uptake and Ca content of the cells. The data suggest that the serum induced changes in Ca content and transport are linked to intracellular cyclic nucleotide levels and progression through G1 phase and that extracellular cAMP elevating agents may enhance or inhibit these interactions in a concentration dependent manner.