Na+/K+/Cl− cotransport is stimulated by a Ca++-calmodulin–;mediated pathway in BALB/c 3T3 fibroblasts

✍ Scribed by David Snyder; Henri Atlan; Miriam Markus; Rivka Panet

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 645 KB
• Volume: 149
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041490320

✦ Synopsis

9 1 120, h a e l

In the present study, we investigated the role of intracellular Ca++ in the stimulation of the Na+/K+/CI-cotransport in synchronized BALB/c 3T3 cells.

The Na+/K+/CI-cotransport was stimulated by the growth factors EGF, TGF-a, IGF-1, and IGF-2, which do not activate protein kinase C, but do induce a transient increase in free cytoplasmic Ca++. In addition, direct activation of protein kinase C by the phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate (TPA) did not affect the Na+/K+/CI-cotransport activity of quiescent cells. The Na+/K+/CI-cotransport was also stimulated by the above mitogens in cells pretreated with the phorbol ester TPA. This treatment led to a progressive decline in the activity of cellular protein kinase C. This result implies that cells deficient in protein kinase C may still support stimulation of the Na+/K+/CI-cotransport. Taken as a whole, these findings suggest that the Na+/K+/CI-cotransport is stimulated predominantly by a protein kinase C-independent mechanism in BALB/c 3T3 fibroblasts.

Both the intracellular Ca++ antagonist 8-(N,N-diethylamino)octyl-3,4,5trimethoxybenzoate (TMB-8) and two potent calmodulin antagonists, trifiuoperazine (TFP) and chloropromazine (CP), blocked serum-and mitogen-stimulated Na+/K+/CI-cotransport. These results suggest that the Na+/K+/CI-cotransport is stimulated by an increase of intracellular Ca++ and subsequently by a Ca++-calmodulin-mediated pathway in the synchronized BALBic 3T3 fibroblasts.