Beta-adrenergic stimulation of Ca2+ fluxes, endocytosis, hexose transport, and amino acid transport in mouse kidney cortex is mediated by polyamine synthesis.

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Abstract
We recently found that the beta-adrenergic agonist 1-isoproterenol evokes a rapid (less than 5 min) Ca2+- and receptor-dependent stimulation of endocytosis, hexose transport, and amino acid transport in mouse renal cortex involving proximal tubule cells. This response is associated with increased Ca2+ fluxes and a mobilization of mitochondrial calcium, suggesting that stimulus-response (stimulus-"transport") coupling is mediated by cytosolic Ca2+. We show here that 1 microM isoproterenol evokes a rapid (less than 60 sec) transient increase in the activity of ornithine decarboxylase followed by an early (less than 2 min) sustained increase in putrescine, spermidine, and spermine concentrations in mouse kidney cortex slices in vitro. Small doses of isoproterenol (down to 24 nmol/kg) elicited a rapid (less than 2 min) increase in polyamines in vivo. The ornithine decarboxylase inhibitor alpha-difluoromethylornithine (5 mM) suppressed the testosterone-induced increase in polyamine levels and rates of endocytosis, hexose transport, and amino acid transport, measured by horseradish peroxidase, [14C]aminoisobutyric acid, and deoxy[3H]glucose uptake. alpha-Difluoromethylornithine also blocked the isoproterenol-induced increase in 45Ca influx and efflux and 45Ca redistribution; 0.5 mM putrescine nullified alpha-difluoromethylornithine inhibition and restored the increment in polyamines, 45Ca fluxes, endocytosis, hexose transport, and amino acid transport. These data implicate polyamine synthesis in isoproterenol stimulation of Ca2+ fluxes and membrane transport processes and support a model for signal transduction and stimulus-response coupling in which ornithine decarboxylase activation and polyamine synthesis play a pivotal role in regulating Ca2+ fluxes. In this model the polyamines generate local Ca2+ signals by stimulating Ca2+ influx or mobilizing intracellular calcium (or both) through a cation exchange reaction.